DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Implementation

Mercurial (dcc6d7a0dc00)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063 1064 1065 1066 1067 1068 1069 1070 1071 1072 1073 1074 1075 1076 1077 1078 1079 1080 1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104 1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175 1176 1177 1178 1179 1180 1181 1182 1183 1184 1185 1186 1187 1188 1189 1190 1191 1192 1193 1194 1195 1196 1197 1198 1199 1200 1201 1202 1203 1204 1205 1206 1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217 1218 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407 1408 1409 1410 1411 1412 1413 1414 1415 1416 1417 1418 1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455 1456 1457 1458 1459 1460 1461 1462 1463 1464 1465 1466 1467 1468 1469 1470 1471 1472 1473 1474 1475 1476 1477 1478 1479 1480 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511 1512 1513 1514 1515 1516 1517 1518 1519 1520 1521 1522 1523 1524 1525 1526 1527 1528 1529 1530 1531 1532 1533 1534 1535 1536 1537 1538 1539 1540 1541 1542 1543 1544 1545 1546 1547 1548 1549 1550 1551 1552 1553 1554 1555 1556 1557 1558 1559 1560 1561 1562 1563 1564 1565 1566 1567 1568 1569 1570 1571 1572 1573 1574 1575 1576 1577 1578 1579 1580 1581 1582 1583 1584 1585 1586 1587 1588 1589 1590 1591 1592 1593 1594 1595 1596 1597 1598 1599 1600 1601 1602 1603 1604 1605 1606 1607 1608 1609 1610 1611 1612 1613 1614 1615 1616 1617 1618 1619 1620 1621 1622 1623 1624 1625 1626 1627 1628 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679 1680 1681 1682 1683 1684 1685 1686 1687 1688 1689 1690 1691 1692 1693 1694 1695 1696 1697 1698 1699 1700 1701 1702 1703 1704 1705 1706 1707 1708 1709 1710 1711 1712 1713 1714 1715 1716 1717 1718 1719 1720 1721 1722 1723 1724 1725 1726 1727 1728 1729 1730 1731 1732 1733 1734 1735 1736 1737 1738 1739 1740 1741 1742 1743 1744 1745 1746 1747 1748 1749 1750 1751 1752 1753 1754 1755 1756 1757 1758 1759 1760 1761 1762 1763 1764 1765 1766 1767 1768 1769 1770 1771 1772 1773 1774 1775 1776 1777 1778 1779 1780 1781 1782 1783 1784 1785 1786 1787 1788 1789 1790 1791 1792 1793 1794 1795 1796 1797 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847 1848 1849 1850 1851 1852 1853 1854 1855 1856 1857 1858 1859 1860 1861 1862 1863 1864 1865 1866 1867 1868 1869 1870 1871 1872 1873 1874 1875 1876 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936 1937 1938 1939 1940 1941 1942 1943 1944 1945 1946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031 2032 2033 2034 2035 2036 2037 2038 2039 2040 2041 2042 2043 2044 2045 2046 2047 2048 2049 2050 2051 2052 2053 2054 2055 2056 2057 2058 2059 2060 2061 2062 2063 2064 2065 2066 2067 2068 2069 2070 2071 2072 2073 2074 2075 2076 2077 2078 2079 2080 2081 2082 2083 2084 2085 2086 2087 2088 2089 2090 2091 2092 2093 2094 2095 2096 2097 2098 2099 2100 2101 2102 2103 2104 2105 2106 2107 2108 2109 2110 2111 2112 2113 2114 2115 2116 2117 2118 2119 2120 2121 2122 2123 2124 2125 2126 2127 2128 2129 2130 2131 2132 2133 2134 2135 2136 2137 2138 2139 2140 2141 2142 2143 2144 2145 2146 2147 2148 2149 2150 2151 2152 2153 2154 2155 2156 2157 2158 2159 2160 2161 2162 2163 2164 2165 2166 2167 2168 2169 2170 2171 2172 2173 2174 2175 2176 2177 2178 2179 2180 2181 2182 2183 2184 2185 2186 2187 2188 2189 2190 2191 2192 2193 2194 2195 2196 2197 2198 2199 2200 2201 2202 2203 2204 2205 2206 2207 2208 2209 2210 2211 2212 2213 2214 2215 2216 2217 2218 2219 2220 2221 2222 2223 2224 2225 2226 2227 2228 2229 2230 2231 2232 2233 2234 2235 2236 2237 2238 2239 2240 2241 2242 2243 2244 2245 2246 2247 2248 2249 2250 2251 2252 2253 2254 2255 2256 2257 2258 2259 2260 2261 2262 2263 2264 2265 2266 2267 2268 2269 2270 2271 2272 2273 2274 2275 2276 2277 2278 2279 2280 2281 2282 2283 2284 2285 2286 2287 2288 2289 2290 2291 2292 2293 2294 2295 2296 2297 2298 2299 2300 2301 2302 2303 2304 2305 2306 2307 2308 2309 2310 2311 2312 2313 2314 2315 2316 2317 2318 2319 2320 2321 2322 2323 2324 2325 2326 2327 2328 2329 2330 2331 2332 2333 2334 2335 2336 2337 2338 2339 2340 2341 2342 2343 2344 2345 2346 2347 2348 2349 2350 2351 2352 2353 2354 2355 2356 2357 2358 2359 2360 2361 2362 2363 2364 2365 2366 2367 2368 2369 2370 2371 2372 2373 2374 2375 2376 2377 2378 2379 2380 2381 2382 2383 2384 2385 2386 2387 2388 2389 2390 2391 2392 2393 2394 2395 2396 2397 2398 2399 2400 2401 2402 2403 2404 2405 2406 2407 2408 2409 2410 2411 2412 2413 2414 2415 2416 2417 2418 2419 2420 2421 2422 2423 2424 2425 2426 2427 2428 2429 2430 2431 2432 2433 2434 2435 2436 2437 2438 2439 2440 2441 2442 2443 2444 2445 2446 2447 2448 2449 2450 2451 2452 2453 2454 2455 2456 2457 2458 2459 2460 2461 2462 2463 2464 2465 2466 2467 2468 2469 2470 2471 2472 2473 2474 2475 2476 2477 2478 2479 2480 2481 2482 2483 2484 2485 2486 2487 2488 2489 2490 2491 2492 2493 2494 2495 2496 2497 2498 2499 2500 2501 2502 2503 2504 2505 2506 2507 2508 2509
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef GFX_LAYERS_H
#define GFX_LAYERS_H

#include <stdint.h>                     // for uint32_t, uint64_t, uint8_t
#include <stdio.h>                      // for FILE
#include <sys/types.h>                  // for int32_t, int64_t
#include "FrameMetrics.h"               // for FrameMetrics
#include "Units.h"                      // for LayerMargin, LayerPoint, ParentLayerIntRect
#include "gfxContext.h"
#include "gfxTypes.h"
#include "gfxPoint.h"                   // for gfxPoint
#include "gfxRect.h"                    // for gfxRect
#include "gfx2DGlue.h"
#include "mozilla/Assertions.h"         // for MOZ_ASSERT_HELPER2, etc
#include "mozilla/DebugOnly.h"          // for DebugOnly
#include "mozilla/EventForwards.h"      // for nsPaintEvent
#include "mozilla/Maybe.h"              // for Maybe
#include "mozilla/RefPtr.h"             // for already_AddRefed
#include "mozilla/StyleAnimationValue.h" // for StyleAnimationValue, etc
#include "mozilla/TimeStamp.h"          // for TimeStamp, TimeDuration
#include "mozilla/UniquePtr.h"          // for UniquePtr
#include "mozilla/gfx/BaseMargin.h"     // for BaseMargin
#include "mozilla/gfx/BasePoint.h"      // for BasePoint
#include "mozilla/gfx/Point.h"          // for IntSize
#include "mozilla/gfx/Types.h"          // for SurfaceFormat
#include "mozilla/gfx/UserData.h"       // for UserData, etc
#include "mozilla/layers/LayersTypes.h"
#include "mozilla/mozalloc.h"           // for operator delete, etc
#include "nsAutoPtr.h"                  // for nsAutoPtr, nsRefPtr, etc
#include "nsCOMPtr.h"                   // for already_AddRefed
#include "nsCSSProperty.h"              // for nsCSSProperty
#include "nsDebug.h"                    // for NS_ASSERTION
#include "nsISupportsImpl.h"            // for Layer::Release, etc
#include "nsRect.h"                     // for mozilla::gfx::IntRect
#include "nsRegion.h"                   // for nsIntRegion
#include "nsString.h"                   // for nsCString
#include "nsTArray.h"                   // for nsTArray
#include "nsTArrayForwardDeclare.h"     // for InfallibleTArray
#include "nscore.h"                     // for nsACString, nsAString
#include "mozilla/Logging.h"                      // for PRLogModuleInfo
#include "nsIWidget.h"                  // For plugin window configuration information structs
#include "gfxVR.h"
#include "ImageContainer.h"

class gfxContext;

extern uint8_t gLayerManagerLayerBuilder;

namespace mozilla {

class ComputedTimingFunction;
class FrameLayerBuilder;
class StyleAnimationValue;

namespace gl {
class GLContext;
} // namespace gl

namespace gfx {
class DrawTarget;
} // namespace gfx

namespace dom {
class OverfillCallback;
} // namespace dom

namespace layers {

class Animation;
class AnimationData;
class AsyncCanvasRenderer;
class AsyncPanZoomController;
class ClientLayerManager;
class Layer;
class LayerMetricsWrapper;
class PaintedLayer;
class ContainerLayer;
class ImageLayer;
class ColorLayer;
class CanvasLayer;
class ReadbackLayer;
class ReadbackProcessor;
class RefLayer;
class LayerComposite;
class ShadowableLayer;
class ShadowLayerForwarder;
class LayerManagerComposite;
class SpecificLayerAttributes;
class Compositor;
class FrameUniformityData;
class PersistentBufferProvider;

namespace layerscope {
class LayersPacket;
} // namespace layerscope

#define MOZ_LAYER_DECL_NAME(n, e)                              \
  virtual const char* Name() const override { return n; }  \
  virtual LayerType GetType() const override { return e; }

// Defined in LayerUserData.h; please include that file instead.
class LayerUserData;

/*
 * Motivation: For truly smooth animation and video playback, we need to
 * be able to compose frames and render them on a dedicated thread (i.e.
 * off the main thread where DOM manipulation, script execution and layout
 * induce difficult-to-bound latency). This requires Gecko to construct
 * some kind of persistent scene structure (graph or tree) that can be
 * safely transmitted across threads. We have other scenarios (e.g. mobile
 * browsing) where retaining some rendered data between paints is desired
 * for performance, so again we need a retained scene structure.
 *
 * Our retained scene structure is a layer tree. Each layer represents
 * content which can be composited onto a destination surface; the root
 * layer is usually composited into a window, and non-root layers are
 * composited into their parent layers. Layers have attributes (e.g.
 * opacity and clipping) that influence their compositing.
 *
 * We want to support a variety of layer implementations, including
 * a simple "immediate mode" implementation that doesn't retain any
 * rendered data between paints (i.e. uses cairo in just the way that
 * Gecko used it before layers were introduced). But we also don't want
 * to have bifurcated "layers"/"non-layers" rendering paths in Gecko.
 * Therefore the layers API is carefully designed to permit maximally
 * efficient implementation in an "immediate mode" style. See the
 * BasicLayerManager for such an implementation.
 */

/**
 * A LayerManager controls a tree of layers. All layers in the tree
 * must use the same LayerManager.
 *
 * All modifications to a layer tree must happen inside a transaction.
 * Only the state of the layer tree at the end of a transaction is
 * rendered. Transactions cannot be nested
 *
 * Each transaction has two phases:
 * 1) Construction: layers are created, inserted, removed and have
 * properties set on them in this phase.
 * BeginTransaction and BeginTransactionWithTarget start a transaction in
 * the Construction phase.
 * 2) Drawing: PaintedLayers are rendered into in this phase, in tree
 * order. When the client has finished drawing into the PaintedLayers, it should
 * call EndTransaction to complete the transaction.
 *
 * All layer API calls happen on the main thread.
 *
 * Layers are refcounted. The layer manager holds a reference to the
 * root layer, and each container layer holds a reference to its children.
 */
class LayerManager {
  NS_INLINE_DECL_REFCOUNTING(LayerManager)

protected:
  typedef mozilla::gfx::DrawTarget DrawTarget;
  typedef mozilla::gfx::IntSize IntSize;
  typedef mozilla::gfx::SurfaceFormat SurfaceFormat;

public:
  LayerManager()
    : mDestroyed(false)
    , mSnapEffectiveTransforms(true)
    , mId(0)
    , mInTransaction(false)
  {}

  /**
   * Release layers and resources held by this layer manager, and mark
   * it as destroyed.  Should do any cleanup necessary in preparation
   * for its widget going away.  After this call, only user data calls
   * are valid on the layer manager.
   */
  virtual void Destroy()
  {
    mDestroyed = true;
    mUserData.Destroy();
    mRoot = nullptr;
  }
  bool IsDestroyed() { return mDestroyed; }

  virtual ShadowLayerForwarder* AsShadowForwarder()
  { return nullptr; }

  virtual LayerManagerComposite* AsLayerManagerComposite()
  { return nullptr; }

  virtual ClientLayerManager* AsClientLayerManager()
  { return nullptr; }

  /**
   * Returns true if this LayerManager is owned by an nsIWidget,
   * and is used for drawing into the widget.
   */
  virtual bool IsWidgetLayerManager() { return true; }
  virtual bool IsInactiveLayerManager() { return false; }

  /**
   * Start a new transaction. Nested transactions are not allowed so
   * there must be no transaction currently in progress.
   * This transaction will update the state of the window from which
   * this LayerManager was obtained.
   */
  virtual void BeginTransaction() = 0;
  /**
   * Start a new transaction. Nested transactions are not allowed so
   * there must be no transaction currently in progress.
   * This transaction will render the contents of the layer tree to
   * the given target context. The rendering will be complete when
   * EndTransaction returns.
   */
  virtual void BeginTransactionWithTarget(gfxContext* aTarget) = 0;

  enum EndTransactionFlags {
    END_DEFAULT = 0,
    END_NO_IMMEDIATE_REDRAW = 1 << 0,  // Do not perform the drawing phase
    END_NO_COMPOSITE = 1 << 1, // Do not composite after drawing painted layer contents.
    END_NO_REMOTE_COMPOSITE = 1 << 2 // Do not schedule a composition with a remote Compositor, if one exists.
  };

  FrameLayerBuilder* GetLayerBuilder() {
    return reinterpret_cast<FrameLayerBuilder*>(GetUserData(&gLayerManagerLayerBuilder));
  }

  /**
   * Attempts to end an "empty transaction". There must have been no
   * changes to the layer tree since the BeginTransaction().
   * It's possible for this to fail; PaintedLayers may need to be updated
   * due to VRAM data being lost, for example. In such cases this method
   * returns false, and the caller must proceed with a normal layer tree
   * update and EndTransaction.
   */
  virtual bool EndEmptyTransaction(EndTransactionFlags aFlags = END_DEFAULT) = 0;

  /**
   * Function called to draw the contents of each PaintedLayer.
   * aRegionToDraw contains the region that needs to be drawn.
   * This would normally be a subregion of the visible region.
   * The callee must draw all of aRegionToDraw. Drawing outside
   * aRegionToDraw will be clipped out or ignored.
   * The callee must draw all of aRegionToDraw.
   * This region is relative to 0,0 in the PaintedLayer.
   *
   * aDirtyRegion should contain the total region that is be due to be painted
   * during the transaction, even though only aRegionToDraw should be drawn
   * during this call. aRegionToDraw must be entirely contained within
   * aDirtyRegion. If the total dirty region is unknown it is okay to pass a
   * subregion of the total dirty region, e.g. just aRegionToDraw, though it
   * may not be as efficient.
   *
   * aRegionToInvalidate contains a region whose contents have been
   * changed by the layer manager and which must therefore be invalidated.
   * For example, this could be non-empty if a retained layer internally
   * switches from RGBA to RGB or back ... we might want to repaint it to
   * consistently use subpixel-AA or not.
   * This region is relative to 0,0 in the PaintedLayer.
   * aRegionToInvalidate may contain areas that are outside
   * aRegionToDraw; the callee must ensure that these areas are repainted
   * in the current layer manager transaction or in a later layer
   * manager transaction.
   *
   * aContext must not be used after the call has returned.
   * We guarantee that buffered contents in the visible
   * region are valid once drawing is complete.
   *
   * The origin of aContext is 0,0 in the PaintedLayer.
   */
  typedef void (* DrawPaintedLayerCallback)(PaintedLayer* aLayer,
                                           gfxContext* aContext,
                                           const nsIntRegion& aRegionToDraw,
                                           const nsIntRegion& aDirtyRegion,
                                           DrawRegionClip aClip,
                                           const nsIntRegion& aRegionToInvalidate,
                                           void* aCallbackData);

  /**
   * Finish the construction phase of the transaction, perform the
   * drawing phase, and end the transaction.
   * During the drawing phase, all PaintedLayers in the tree are
   * drawn in tree order, exactly once each, except for those layers
   * where it is known that the visible region is empty.
   */
  virtual void EndTransaction(DrawPaintedLayerCallback aCallback,
                              void* aCallbackData,
                              EndTransactionFlags aFlags = END_DEFAULT) = 0;

  /**
   * Schedule a composition with the remote Compositor, if one exists
   * for this LayerManager. Useful in conjunction with the END_NO_REMOTE_COMPOSITE
   * flag to EndTransaction.
   */
  virtual void Composite() {}

  virtual bool HasShadowManagerInternal() const { return false; }
  bool HasShadowManager() const { return HasShadowManagerInternal(); }
  virtual void StorePluginWidgetConfigurations(const nsTArray<nsIWidget::Configuration>& aConfigurations) {}
  bool IsSnappingEffectiveTransforms() { return mSnapEffectiveTransforms; }


  /**
   * Returns true if the layer manager can't render component alpha
   * layers, and layer building should do it's best to avoid
   * creating them.
   */
  virtual bool ShouldAvoidComponentAlphaLayers() { return false; }

  /**
   * Returns true if this LayerManager can properly support layers with
   * SurfaceMode::SURFACE_COMPONENT_ALPHA. LayerManagers that can't will use
   * transparent surfaces (and lose subpixel-AA for text).
   */
  virtual bool AreComponentAlphaLayersEnabled();

  /**
   * CONSTRUCTION PHASE ONLY
   * Set the root layer. The root layer is initially null. If there is
   * no root layer, EndTransaction won't draw anything.
   */
  virtual void SetRoot(Layer* aLayer) = 0;
  /**
   * Can be called anytime
   */
  Layer* GetRoot() { return mRoot; }

  /**
   * Does a breadth-first search from the root layer to find the first
   * scrollable layer, and returns its ViewID. Note that there may be
   * other layers in the tree which share the same ViewID.
   * Can be called any time.
   */
  FrameMetrics::ViewID GetRootScrollableLayerId();

  /**
   * Does a breadth-first search from the root layer to find the first
   * scrollable layer, and returns all the layers that have that ViewID
   * as the first scrollable metrics in their ancestor chain. If no
   * scrollable layers are found it just returns the root of the tree if
   * there is one.
   */
  void GetRootScrollableLayers(nsTArray<Layer*>& aArray);

  /**
   * Returns a list of all descendant layers for which
   * GetFrameMetrics().IsScrollable() is true and that
   * do not already have an ancestor in the return list.
   */
  void GetScrollableLayers(nsTArray<Layer*>& aArray);

  /**
   * CONSTRUCTION PHASE ONLY
   * Called when a managee has mutated.
   * Subclasses overriding this method must first call their
   * superclass's impl
   */
#ifdef DEBUG
  // In debug builds, we check some properties of |aLayer|.
  virtual void Mutated(Layer* aLayer);
#else
  virtual void Mutated(Layer* aLayer) { }
#endif

  /**
   * Hints that can be used during PaintedLayer creation to influence the type
   * or properties of the layer created.
   *
   * NONE: No hint.
   * SCROLLABLE: This layer may represent scrollable content.
   */
  enum PaintedLayerCreationHint {
    NONE, SCROLLABLE
  };

  /**
   * CONSTRUCTION PHASE ONLY
   * Create a PaintedLayer for this manager's layer tree.
   */
  virtual already_AddRefed<PaintedLayer> CreatePaintedLayer() = 0;
  /**
   * CONSTRUCTION PHASE ONLY
   * Create a PaintedLayer for this manager's layer tree, with a creation hint
   * parameter to help optimise the type of layer created.
   */
  virtual already_AddRefed<PaintedLayer> CreatePaintedLayerWithHint(PaintedLayerCreationHint) {
    return CreatePaintedLayer();
  }
  /**
   * CONSTRUCTION PHASE ONLY
   * Create a ContainerLayer for this manager's layer tree.
   */
  virtual already_AddRefed<ContainerLayer> CreateContainerLayer() = 0;
  /**
   * CONSTRUCTION PHASE ONLY
   * Create an ImageLayer for this manager's layer tree.
   */
  virtual already_AddRefed<ImageLayer> CreateImageLayer() = 0;
  /**
   * CONSTRUCTION PHASE ONLY
   * Create a ColorLayer for this manager's layer tree.
   */
  virtual already_AddRefed<ColorLayer> CreateColorLayer() = 0;
  /**
   * CONSTRUCTION PHASE ONLY
   * Create a CanvasLayer for this manager's layer tree.
   */
  virtual already_AddRefed<CanvasLayer> CreateCanvasLayer() = 0;
  /**
   * CONSTRUCTION PHASE ONLY
   * Create a ReadbackLayer for this manager's layer tree.
   */
  virtual already_AddRefed<ReadbackLayer> CreateReadbackLayer() { return nullptr; }
  /**
   * CONSTRUCTION PHASE ONLY
   * Create a RefLayer for this manager's layer tree.
   */
  virtual already_AddRefed<RefLayer> CreateRefLayer() { return nullptr; }


  /**
   * Can be called anytime, from any thread.
   *
   * Creates an Image container which forwards its images to the compositor within
   * layer transactions on the main thread or asynchronously using the ImageBridge IPDL protocol.
   * In the case of asynchronous, If the protocol is not available, the returned ImageContainer
   * will forward images within layer transactions.
   */
  static already_AddRefed<ImageContainer> CreateImageContainer(ImageContainer::Mode flag
                                                                = ImageContainer::SYNCHRONOUS);

  /**
   * Type of layer manager his is. This is to be used sparsely in order to
   * avoid a lot of Layers backend specific code. It should be used only when
   * Layers backend specific functionality is necessary.
   */
  virtual LayersBackend GetBackendType() = 0;

  /**
   * Type of layers backend that will be used to composite this layer tree.
   * When compositing is done remotely, then this returns the layers type
   * of the compositor.
   */
  virtual LayersBackend GetCompositorBackendType() { return GetBackendType(); }

  /**
   * Creates a DrawTarget which is optimized for inter-operating with this
   * layer manager.
   */
  virtual already_AddRefed<DrawTarget>
    CreateOptimalDrawTarget(const IntSize &aSize,
                            SurfaceFormat imageFormat);

  /**
   * Creates a DrawTarget for alpha masks which is optimized for inter-
   * operating with this layer manager. In contrast to CreateOptimalDrawTarget,
   * this surface is optimised for drawing alpha only and we assume that
   * drawing the mask is fairly simple.
   */
  virtual already_AddRefed<DrawTarget>
    CreateOptimalMaskDrawTarget(const IntSize &aSize);

  /**
   * Creates a DrawTarget for use with canvas which is optimized for
   * inter-operating with this layermanager.
   */
  virtual already_AddRefed<mozilla::gfx::DrawTarget>
    CreateDrawTarget(const mozilla::gfx::IntSize &aSize,
                     mozilla::gfx::SurfaceFormat aFormat);

  /**
   * Creates a PersistentBufferProvider for use with canvas which is optimized for
   * inter-operating with this layermanager.
   */
  virtual already_AddRefed<PersistentBufferProvider>
    CreatePersistentBufferProvider(const mozilla::gfx::IntSize &aSize,
                                   mozilla::gfx::SurfaceFormat aFormat);

  virtual bool CanUseCanvasLayerForSize(const gfx::IntSize &aSize) { return true; }

  /**
   * returns the maximum texture size on this layer backend, or INT32_MAX
   * if there is no maximum
   */
  virtual int32_t GetMaxTextureSize() const = 0;

  /**
   * Return the name of the layer manager's backend.
   */
  virtual void GetBackendName(nsAString& aName) = 0;

  /**
   * This setter can be used anytime. The user data for all keys is
   * initially null. Ownership pases to the layer manager.
   */
  void SetUserData(void* aKey, LayerUserData* aData)
  {
    mUserData.Add(static_cast<gfx::UserDataKey*>(aKey), aData, LayerUserDataDestroy);
  }
  /**
   * This can be used anytime. Ownership passes to the caller!
   */
  nsAutoPtr<LayerUserData> RemoveUserData(void* aKey);

  /**
   * This getter can be used anytime.
   */
  bool HasUserData(void* aKey)
  {
    return mUserData.Has(static_cast<gfx::UserDataKey*>(aKey));
  }
  /**
   * This getter can be used anytime. Ownership is retained by the layer
   * manager.
   */
  LayerUserData* GetUserData(void* aKey) const
  {
    return static_cast<LayerUserData*>(mUserData.Get(static_cast<gfx::UserDataKey*>(aKey)));
  }

  /**
   * Must be called outside of a layers transaction.
   *
   * For the subtree rooted at |aSubtree|, this attempts to free up
   * any free-able resources like retained buffers, but may do nothing
   * at all.  After this call, the layer tree is left in an undefined
   * state; the layers in |aSubtree|'s subtree may no longer have
   * buffers with valid content and may no longer be able to draw
   * their visible and valid regions.
   *
   * In general, a painting or forwarding transaction on |this| must
   * complete on the tree before it returns to a valid state.
   *
   * Resource freeing begins from |aSubtree| or |mRoot| if |aSubtree|
   * is null.  |aSubtree|'s manager must be this.
   */
  virtual void ClearCachedResources(Layer* aSubtree = nullptr) {}

  /**
   * Flag the next paint as the first for a document.
   */
  virtual void SetIsFirstPaint() {}

  /**
   * Make sure that the previous transaction has been entirely
   * completed.
   *
   * Note: This may sychronously wait on a remote compositor
   * to complete rendering.
   */
  virtual void FlushRendering() { }

  /**
   * Checks if we need to invalidate the OS widget to trigger
   * painting when updating this layer manager.
   */
  virtual bool NeedsWidgetInvalidation() { return true; }

  virtual const char* Name() const { return "???"; }

  /**
   * Dump information about this layer manager and its managed tree to
   * aStream.
   */
  void Dump(std::stringstream& aStream, const char* aPrefix="", bool aDumpHtml=false);
  /**
   * Dump information about just this layer manager itself to aStream
   */
  void DumpSelf(std::stringstream& aStream, const char* aPrefix="");
  void Dump();

  /**
   * Dump information about this layer manager and its managed tree to
   * layerscope packet.
   */
  void Dump(layerscope::LayersPacket* aPacket);

  /**
   * Log information about this layer manager and its managed tree to
   * the NSPR log (if enabled for "Layers").
   */
  void Log(const char* aPrefix="");
  /**
   * Log information about just this layer manager itself to the NSPR
   * log (if enabled for "Layers").
   */
  void LogSelf(const char* aPrefix="");

  /**
   * Record (and return) frame-intervals and paint-times for frames which were presented
   *   between calling StartFrameTimeRecording and StopFrameTimeRecording.
   *
   * - Uses a cyclic buffer and serves concurrent consumers, so if Stop is called too late
   *     (elements were overwritten since Start), result is considered invalid and hence empty.
   * - Buffer is capable of holding 10 seconds @ 60fps (or more if frames were less frequent).
   *     Can be changed (up to 1 hour) via pref: toolkit.framesRecording.bufferSize.
   * - Note: the first frame-interval may be longer than expected because last frame
   *     might have been presented some time before calling StartFrameTimeRecording.
   */

  /**
   * Returns a handle which represents current recording start position.
   */
  virtual uint32_t StartFrameTimeRecording(int32_t aBufferSize);

  /**
   *  Clears, then populates aFrameIntervals with the recorded frame timing
   *  data. The array will be empty if data was overwritten since
   *  aStartIndex was obtained.
   */
  virtual void StopFrameTimeRecording(uint32_t         aStartIndex,
                                      nsTArray<float>& aFrameIntervals);

  void RecordFrame();
  void PostPresent();

  void BeginTabSwitch();

  static bool IsLogEnabled();
  static mozilla::LogModule* GetLog();

  bool IsCompositingCheap(LayersBackend aBackend)
  {
    // LayersBackend::LAYERS_NONE is an error state, but in that case we should try to
    // avoid loading the compositor!
    return LayersBackend::LAYERS_BASIC != aBackend && LayersBackend::LAYERS_NONE != aBackend;
  }

  virtual bool IsCompositingCheap() { return true; }

  bool IsInTransaction() const { return mInTransaction; }
  virtual void GetFrameUniformity(FrameUniformityData* aOutData) { }
  virtual bool RequestOverfill(mozilla::dom::OverfillCallback* aCallback) { return true; }
  virtual void RunOverfillCallback(const uint32_t aOverfill) { }

  virtual void SetRegionToClear(const nsIntRegion& aRegion)
  {
    mRegionToClear = aRegion;
  }

  virtual bool SupportsMixBlendModes(EnumSet<gfx::CompositionOp>& aMixBlendModes)
  {
    return false;
  }

  bool SupportsMixBlendMode(gfx::CompositionOp aMixBlendMode)
  {
    EnumSet<gfx::CompositionOp> modes(aMixBlendMode);
    return SupportsMixBlendModes(modes);
  }

  virtual float RequestProperty(const nsAString& property) { return -1; }

  const TimeStamp& GetAnimationReadyTime() const {
    return mAnimationReadyTime;
  }

  virtual bool AsyncPanZoomEnabled() const {
    return false;
  }

  static void LayerUserDataDestroy(void* data);

protected:
  RefPtr<Layer> mRoot;
  gfx::UserData mUserData;
  bool mDestroyed;
  bool mSnapEffectiveTransforms;

  nsIntRegion mRegionToClear;

  // Protected destructor, to discourage deletion outside of Release():
  virtual ~LayerManager() {}

  // Print interesting information about this into aStreamo.  Internally
  // used to implement Dump*() and Log*().
  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix);

  // Print interesting information about this into layerscope packet.
  // Internally used to implement Dump().
  virtual void DumpPacket(layerscope::LayersPacket* aPacket);

  uint64_t mId;
  bool mInTransaction;
  // The time when painting most recently finished. This is recorded so that
  // we can time any play-pending animations from this point.
  TimeStamp mAnimationReadyTime;
private:
  struct FramesTimingRecording
  {
    // Stores state and data for frame intervals and paint times recording.
    // see LayerManager::StartFrameTimeRecording() at Layers.cpp for more details.
    FramesTimingRecording()
      : mIsPaused(true)
      , mNextIndex(0)
    {}
    bool mIsPaused;
    uint32_t mNextIndex;
    TimeStamp mLastFrameTime;
    nsTArray<float> mIntervals;
    uint32_t mLatestStartIndex;
    uint32_t mCurrentRunStartIndex;
  };
  FramesTimingRecording mRecording;

  TimeStamp mTabSwitchStart;
};

typedef InfallibleTArray<Animation> AnimationArray;

struct AnimData {
  InfallibleTArray<mozilla::StyleAnimationValue> mStartValues;
  InfallibleTArray<mozilla::StyleAnimationValue> mEndValues;
  InfallibleTArray<nsAutoPtr<mozilla::ComputedTimingFunction> > mFunctions;
};

/**
 * A Layer represents anything that can be rendered onto a destination
 * surface.
 */
class Layer {
  NS_INLINE_DECL_REFCOUNTING(Layer)

public:
  // Keep these in alphabetical order
  enum LayerType {
    TYPE_CANVAS,
    TYPE_COLOR,
    TYPE_CONTAINER,
    TYPE_IMAGE,
    TYPE_READBACK,
    TYPE_REF,
    TYPE_SHADOW,
    TYPE_PAINTED
  };

  /**
   * Returns the LayerManager this Layer belongs to. Note that the layer
   * manager might be in a destroyed state, at which point it's only
   * valid to set/get user data from it.
   */
  LayerManager* Manager() { return mManager; }

  enum {
    /**
     * If this is set, the caller is promising that by the end of this
     * transaction the entire visible region (as specified by
     * SetVisibleRegion) will be filled with opaque content.
     */
    CONTENT_OPAQUE = 0x01,
    /**
     * If this is set, the caller is notifying that the contents of this layer
     * require per-component alpha for optimal fidelity. However, there is no
     * guarantee that component alpha will be supported for this layer at
     * paint time.
     * This should never be set at the same time as CONTENT_OPAQUE.
     */
    CONTENT_COMPONENT_ALPHA = 0x02,

    /**
     * If this is set then one of the descendant layers of this one has
     * CONTENT_COMPONENT_ALPHA set.
     */
    CONTENT_COMPONENT_ALPHA_DESCENDANT = 0x04,

    /**
     * If this is set then this layer is part of a preserve-3d group, and should
     * be sorted with sibling layers that are also part of the same group.
     */
    CONTENT_PRESERVE_3D = 0x08,
    /**
     * This indicates that the transform may be changed on during an empty
     * transaction where there is no possibility of redrawing the content, so the
     * implementation should be ready for that.
     */
    CONTENT_MAY_CHANGE_TRANSFORM = 0x10,

    /**
     * Disable subpixel AA for this layer. This is used if the display isn't suited
     * for subpixel AA like hidpi or rotated content.
     */
    CONTENT_DISABLE_SUBPIXEL_AA = 0x20,

    /**
     * If this is set then the layer contains content that may look objectionable
     * if not handled as an active layer (such as text with an animated transform).
     * This is for internal layout/FrameLayerBuilder usage only until flattening
     * code is obsoleted. See bug 633097
     */
    CONTENT_DISABLE_FLATTENING = 0x40
  };
  /**
   * CONSTRUCTION PHASE ONLY
   * This lets layout make some promises about what will be drawn into the
   * visible region of the PaintedLayer. This enables internal quality
   * and performance optimizations.
   */
  void SetContentFlags(uint32_t aFlags)
  {
    NS_ASSERTION((aFlags & (CONTENT_OPAQUE | CONTENT_COMPONENT_ALPHA)) !=
                 (CONTENT_OPAQUE | CONTENT_COMPONENT_ALPHA),
                 "Can't be opaque and require component alpha");
    if (mContentFlags != aFlags) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ContentFlags", this));
      mContentFlags = aFlags;
      Mutated();
    }
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * The union of the bounds of all the display item that got flattened
   * into this layer. This is intended to be an approximation to the
   * size of the layer if the nearest scrollable ancestor had an infinitely
   * large displayport. Computing this more exactly is too expensive,
   * but this approximation is sufficient for what we need to use it for.
   */
  virtual void SetLayerBounds(const gfx::IntRect& aLayerBounds)
  {
    if (!mLayerBounds.IsEqualEdges(aLayerBounds)) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) LayerBounds", this));
      mLayerBounds = aLayerBounds;
      Mutated();
    }
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * Tell this layer which region will be visible. The visible region
   * is a region which contains all the contents of the layer that can
   * actually affect the rendering of the window. It can exclude areas
   * that are covered by opaque contents of other layers, and it can
   * exclude areas where this layer simply contains no content at all.
   * (This can be an overapproximation to the "true" visible region.)
   *
   * There is no general guarantee that drawing outside the bounds of the
   * visible region will be ignored. So if a layer draws outside the bounds
   * of its visible region, it needs to ensure that what it draws is valid.
   */
  virtual void SetVisibleRegion(const LayerIntRegion& aRegion)
  {
    if (!mVisibleRegion.IsEqual(aRegion)) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) VisibleRegion was %s is %s", this,
        mVisibleRegion.ToString().get(), aRegion.ToString().get()));
      mVisibleRegion = aRegion;
      Mutated();
    }
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * Set the (sub)document metrics used to render the Layer subtree
   * rooted at this. Note that a layer may have multiple FrameMetrics
   * objects; calling this function will remove all of them and replace
   * them with the provided FrameMetrics. See the documentation for
   * SetFrameMetrics(const nsTArray<FrameMetrics>&) for more details.
   */
  void SetFrameMetrics(const FrameMetrics& aFrameMetrics)
  {
    if (mFrameMetrics.Length() != 1 || mFrameMetrics[0] != aFrameMetrics) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) FrameMetrics", this));
      mFrameMetrics.ReplaceElementsAt(0, mFrameMetrics.Length(), aFrameMetrics);
      FrameMetricsChanged();
      Mutated();
    }
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * Set the (sub)document metrics used to render the Layer subtree
   * rooted at this. There might be multiple metrics on this layer
   * because the layer may, for example, be contained inside multiple
   * nested scrolling subdocuments. In general a Layer having multiple
   * FrameMetrics objects is conceptually equivalent to having a stack
   * of ContainerLayers that have been flattened into this Layer.
   * See the documentation in LayerMetricsWrapper.h for a more detailed
   * explanation of this conceptual equivalence.
   *
   * Note also that there is actually a many-to-many relationship between
   * Layers and FrameMetrics, because multiple Layers may have identical
   * FrameMetrics objects. This happens when those layers belong to the
   * same scrolling subdocument and therefore end up with the same async
   * transform when they are scrolled by the APZ code.
   */
  void SetFrameMetrics(const nsTArray<FrameMetrics>& aMetricsArray)
  {
    if (mFrameMetrics != aMetricsArray) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) FrameMetrics", this));
      mFrameMetrics = aMetricsArray;
      FrameMetricsChanged();
      Mutated();
    }
  }

  /*
   * Compositor event handling
   * =========================
   * When a touch-start event (or similar) is sent to the AsyncPanZoomController,
   * it needs to decide whether the event should be sent to the main thread.
   * Each layer has a list of event handling regions. When the compositor needs
   * to determine how to handle a touch event, it scans the layer tree from top
   * to bottom in z-order (traversing children before their parents). Points
   * outside the clip region for a layer cause that layer (and its subtree)
   * to be ignored. If a layer has a mask layer, and that mask layer's alpha
   * value is zero at the event point, then the layer and its subtree should
   * be ignored.
   * For each layer, if the point is outside its hit region, we ignore the layer
   * and move onto the next. If the point is inside its hit region but
   * outside the dispatch-to-content region, we can initiate a gesture without
   * consulting the content thread. Otherwise we must dispatch the event to
   * content.
   * Note that if a layer or any ancestor layer has a ForceEmptyHitRegion
   * override in GetEventRegionsOverride() then the hit-region must be treated
   * as empty. Similarly, if there is a ForceDispatchToContent override then
   * the dispatch-to-content region must be treated as encompassing the entire
   * hit region, and therefore we must consult the content thread before
   * initiating a gesture. (If both flags are set, ForceEmptyHitRegion takes
   * priority.)
   */
  /**
   * CONSTRUCTION PHASE ONLY
   * Set the event handling region.
   */
  void SetEventRegions(const EventRegions& aRegions)
  {
    if (mEventRegions != aRegions) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) eventregions were %s, now %s", this,
        mEventRegions.ToString().get(), aRegions.ToString().get()));
      mEventRegions = aRegions;
      Mutated();
    }
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * Set the opacity which will be applied to this layer as it
   * is composited to the destination.
   */
  void SetOpacity(float aOpacity)
  {
    if (mOpacity != aOpacity) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) Opacity", this));
      mOpacity = aOpacity;
      Mutated();
    }
  }

  void SetMixBlendMode(gfx::CompositionOp aMixBlendMode)
  {
    if (mMixBlendMode != aMixBlendMode) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) MixBlendMode", this));
      mMixBlendMode = aMixBlendMode;
      Mutated();
    }
  }

  void SetForceIsolatedGroup(bool aForceIsolatedGroup)
  {
    if(mForceIsolatedGroup != aForceIsolatedGroup) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ForceIsolatedGroup", this));
      mForceIsolatedGroup = aForceIsolatedGroup;
      Mutated();
    }
  }

  bool GetForceIsolatedGroup() const
  {
    return mForceIsolatedGroup;
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * Set a clip rect which will be applied to this layer as it is
   * composited to the destination. The coordinates are relative to
   * the parent layer (i.e. the contents of this layer
   * are transformed before this clip rect is applied).
   * For the root layer, the coordinates are relative to the widget,
   * in device pixels.
   * If aRect is null no clipping will be performed.
   */
  void SetClipRect(const Maybe<ParentLayerIntRect>& aRect)
  {
    if (mClipRect) {
      if (!aRect) {
        MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ClipRect was %d,%d,%d,%d is <none>", this,
                         mClipRect->x, mClipRect->y, mClipRect->width, mClipRect->height));
        mClipRect.reset();
        Mutated();
      } else {
        if (!aRect->IsEqualEdges(*mClipRect)) {
          MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ClipRect was %d,%d,%d,%d is %d,%d,%d,%d", this,
                           mClipRect->x, mClipRect->y, mClipRect->width, mClipRect->height,
                           aRect->x, aRect->y, aRect->width, aRect->height));
          mClipRect = aRect;
          Mutated();
        }
      }
    } else {
      if (aRect) {
        MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ClipRect was <none> is %d,%d,%d,%d", this,
                         aRect->x, aRect->y, aRect->width, aRect->height));
        mClipRect = aRect;
        Mutated();
      }
    }
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * Set a layer to mask this layer.
   *
   * The mask layer should be applied using its effective transform (after it
   * is calculated by ComputeEffectiveTransformForMaskLayer), this should use
   * this layer's parent's transform and the mask layer's transform, but not
   * this layer's. That is, the mask layer is specified relative to this layer's
   * position in it's parent layer's coord space.
   * Currently, only 2D translations are supported for the mask layer transform.
   *
   * Ownership of aMaskLayer passes to this.
   * Typical use would be an ImageLayer with an alpha image used for masking.
   * See also ContainerState::BuildMaskLayer in FrameLayerBuilder.cpp.
   */
  void SetMaskLayer(Layer* aMaskLayer)
  {
#ifdef DEBUG
    if (aMaskLayer) {
      bool maskIs2D = aMaskLayer->GetTransform().CanDraw2D();
      NS_ASSERTION(maskIs2D, "Mask layer has invalid transform.");
    }
#endif

    if (mMaskLayer != aMaskLayer) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) MaskLayer", this));
      mMaskLayer = aMaskLayer;
      Mutated();
    }
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * Add a FrameMetrics-associated mask layer.
   */
  void SetAncestorMaskLayers(const nsTArray<RefPtr<Layer>>& aLayers) {
    if (aLayers != mAncestorMaskLayers) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) AncestorMaskLayers", this));
      mAncestorMaskLayers = aLayers;
      Mutated();
    }
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * Tell this layer what its transform should be. The transformation
   * is applied when compositing the layer into its parent container.
   */
  void SetBaseTransform(const gfx::Matrix4x4& aMatrix)
  {
    NS_ASSERTION(!aMatrix.IsSingular(),
                 "Shouldn't be trying to draw with a singular matrix!");
    mPendingTransform = nullptr;
    if (mTransform == aMatrix) {
      return;
    }
    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) BaseTransform", this));
    mTransform = aMatrix;
    Mutated();
  }

  /**
   * Can be called at any time.
   *
   * Like SetBaseTransform(), but can be called before the next
   * transform (i.e. outside an open transaction).  Semantically, this
   * method enqueues a new transform value to be set immediately after
   * the next transaction is opened.
   */
  void SetBaseTransformForNextTransaction(const gfx::Matrix4x4& aMatrix)
  {
    mPendingTransform = new gfx::Matrix4x4(aMatrix);
  }

  void SetPostScale(float aXScale, float aYScale)
  {
    if (mPostXScale == aXScale && mPostYScale == aYScale) {
      return;
    }
    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) PostScale", this));
    mPostXScale = aXScale;
    mPostYScale = aYScale;
    Mutated();
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * A layer is "fixed position" when it draws content from a content
   * (not chrome) document, the topmost content document has a root scrollframe
   * with a displayport, but the layer does not move when that displayport scrolls.
   */
  void SetIsFixedPosition(bool aFixedPosition)
  {
    if (mIsFixedPosition != aFixedPosition) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) IsFixedPosition", this));
      mIsFixedPosition = aFixedPosition;
      Mutated();
    }
  }

  // Call AddAnimation to add a new animation to this layer from layout code.
  // Caller must fill in all the properties of the returned animation.
  // A later animation overrides an earlier one.
  Animation* AddAnimation();
  // ClearAnimations clears animations on this layer.
  void ClearAnimations();
  // This is only called when the layer tree is updated. Do not call this from
  // layout code.  To add an animation to this layer, use AddAnimation.
  void SetAnimations(const AnimationArray& aAnimations);
  // Go through all animations in this layer and its children and, for
  // any animations with a null start time, update their start time such
  // that at |aReadyTime| the animation's current time corresponds to its
  // 'initial current time' value.
  void StartPendingAnimations(const TimeStamp& aReadyTime);

  // These are a parallel to AddAnimation and clearAnimations, except
  // they add pending animations that apply only when the next
  // transaction is begun.  (See also
  // SetBaseTransformForNextTransaction.)
  Animation* AddAnimationForNextTransaction();
  void ClearAnimationsForNextTransaction();

  /**
   * CONSTRUCTION PHASE ONLY
   * If a layer represents a fixed position element, this data is stored on the
   * layer for use by the compositor.
   *
   *   - |aScrollId| identifies the scroll frame that this element is fixed
   *     with respect to.
   *
   *   - |aAnchor| is the point on the layer that is considered the "anchor"
   *     point, that is, the point which remains in the same position when
   *     compositing the layer tree with a transformation (such as when
   *     asynchronously scrolling and zooming).
   *
   *   - |aSides| is the set of sides to which the element is fixed relative to.
   *     This is used if the viewport size is changed in the compositor and
   *     fixed position items need to shift accordingly. This value is made up
   *     combining appropriate values from mozilla::SideBits.
   *
   *   - |aIsClipFixed| is true if this layer's clip rect and mask layer
   *     should also remain fixed during async scrolling/animations.
   *     This is the case for fixed position layers, but not for
   *     fixed background layers.
   */
  void SetFixedPositionData(FrameMetrics::ViewID aScrollId,
                            const LayerPoint& aAnchor,
                            int32_t aSides,
                            bool aIsClipFixed)
  {
    if (!mFixedPositionData ||
        mFixedPositionData->mScrollId != aScrollId ||
        mFixedPositionData->mAnchor != aAnchor ||
        mFixedPositionData->mSides != aSides ||
        mFixedPositionData->mIsClipFixed != aIsClipFixed) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) FixedPositionData", this));
      if (!mFixedPositionData) {
        mFixedPositionData = MakeUnique<FixedPositionData>();
      }
      mFixedPositionData->mScrollId = aScrollId;
      mFixedPositionData->mAnchor = aAnchor;
      mFixedPositionData->mSides = aSides;
      mFixedPositionData->mIsClipFixed = aIsClipFixed;
      Mutated();
    }
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * If a layer is "sticky position", |aScrollId| holds the scroll identifier
   * of the scrollable content that contains it. The difference between the two
   * rectangles |aOuter| and |aInner| is treated as two intervals in each
   * dimension, with the current scroll position at the origin. For each
   * dimension, while that component of the scroll position lies within either
   * interval, the layer should not move relative to its scrolling container.
   */
  void SetStickyPositionData(FrameMetrics::ViewID aScrollId, LayerRect aOuter,
                             LayerRect aInner)
  {
    if (!mStickyPositionData ||
        !mStickyPositionData->mOuter.IsEqualEdges(aOuter) ||
        !mStickyPositionData->mInner.IsEqualEdges(aInner)) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) StickyPositionData", this));
      if (!mStickyPositionData) {
        mStickyPositionData = new StickyPositionData;
      }
      mStickyPositionData->mScrollId = aScrollId;
      mStickyPositionData->mOuter = aOuter;
      mStickyPositionData->mInner = aInner;
      Mutated();
    }
  }

  enum ScrollDirection {
    NONE,
    VERTICAL,
    HORIZONTAL
  };

  /**
   * CONSTRUCTION PHASE ONLY
   * If a layer is a scrollbar layer, |aScrollId| holds the scroll identifier
   * of the scrollable content that the scrollbar is for.
   */
  void SetScrollbarData(FrameMetrics::ViewID aScrollId, ScrollDirection aDir, float aThumbRatio)
  {
    if (mScrollbarTargetId != aScrollId ||
        mScrollbarDirection != aDir ||
        mScrollbarThumbRatio != aThumbRatio)
    {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ScrollbarData", this));
      mScrollbarTargetId = aScrollId;
      mScrollbarDirection = aDir;
      mScrollbarThumbRatio = aThumbRatio;
      Mutated();
    }
  }

  // Set during construction for the container layer of scrollbar components.
  void SetIsScrollbarContainer()
  {
    if (!mIsScrollbarContainer) {
      mIsScrollbarContainer = true;
      Mutated();
    }
  }

  // These getters can be used anytime.
  float GetOpacity() { return mOpacity; }
  gfx::CompositionOp GetMixBlendMode() const { return mMixBlendMode; }
  const Maybe<ParentLayerIntRect>& GetClipRect() const { return mClipRect; }
  uint32_t GetContentFlags() { return mContentFlags; }
  const gfx::IntRect& GetLayerBounds() const { return mLayerBounds; }
  const LayerIntRegion& GetVisibleRegion() const { return mVisibleRegion; }
  const FrameMetrics& GetFrameMetrics(uint32_t aIndex) const;
  uint32_t GetFrameMetricsCount() const { return mFrameMetrics.Length(); }
  const nsTArray<FrameMetrics>& GetAllFrameMetrics() { return mFrameMetrics; }
  bool HasScrollableFrameMetrics() const;
  bool IsScrollInfoLayer() const;
  const EventRegions& GetEventRegions() const { return mEventRegions; }
  ContainerLayer* GetParent() { return mParent; }
  Layer* GetNextSibling() { return mNextSibling; }
  const Layer* GetNextSibling() const { return mNextSibling; }
  Layer* GetPrevSibling() { return mPrevSibling; }
  const Layer* GetPrevSibling() const { return mPrevSibling; }
  virtual Layer* GetFirstChild() const { return nullptr; }
  virtual Layer* GetLastChild() const { return nullptr; }
  const gfx::Matrix4x4 GetTransform() const;
  const gfx::Matrix4x4& GetBaseTransform() const { return mTransform; }
  // Note: these are virtual because ContainerLayerComposite overrides them.
  virtual float GetPostXScale() const { return mPostXScale; }
  virtual float GetPostYScale() const { return mPostYScale; }
  bool GetIsFixedPosition() { return mIsFixedPosition; }
  bool GetIsStickyPosition() { return mStickyPositionData; }
  FrameMetrics::ViewID GetFixedPositionScrollContainerId() { return mFixedPositionData ? mFixedPositionData->mScrollId : FrameMetrics::NULL_SCROLL_ID; }
  LayerPoint GetFixedPositionAnchor() { return mFixedPositionData ? mFixedPositionData->mAnchor : LayerPoint(); }
  int32_t GetFixedPositionSides() { return mFixedPositionData ? mFixedPositionData->mSides : eSideBitsNone; }
  bool IsClipFixed() { return mFixedPositionData ? mFixedPositionData->mIsClipFixed : false; }
  FrameMetrics::ViewID GetStickyScrollContainerId() { return mStickyPositionData->mScrollId; }
  const LayerRect& GetStickyScrollRangeOuter() { return mStickyPositionData->mOuter; }
  const LayerRect& GetStickyScrollRangeInner() { return mStickyPositionData->mInner; }
  FrameMetrics::ViewID GetScrollbarTargetContainerId() { return mScrollbarTargetId; }
  ScrollDirection GetScrollbarDirection() { return mScrollbarDirection; }
  float GetScrollbarThumbRatio() { return mScrollbarThumbRatio; }
  bool IsScrollbarContainer() { return mIsScrollbarContainer; }
  Layer* GetMaskLayer() const { return mMaskLayer; }

  // Ancestor mask layers are associated with FrameMetrics, but for simplicity
  // in maintaining the layer tree structure we attach them to the layer.
  size_t GetAncestorMaskLayerCount() const {
    return mAncestorMaskLayers.Length();
  }
  Layer* GetAncestorMaskLayerAt(size_t aIndex) const {
    return mAncestorMaskLayers.ElementAt(aIndex);
  }

  bool HasMaskLayers() const {
    return GetMaskLayer() || mAncestorMaskLayers.Length() > 0;
  }

  /*
   * Get the combined clip rect of the Layer clip and all clips on FrameMetrics.
   * This is intended for use in Layout. The compositor needs to apply async
   * transforms to find the combined clip.
   */
  Maybe<ParentLayerIntRect> GetCombinedClipRect() const;

  /**
   * Retrieve the root level visible region for |this| taking into account
   * clipping applied to parent layers of |this| as well as subtracting
   * visible regions of higher siblings of this layer and each ancestor.
   *
   * Note translation values for offsets of visible regions and accumulated
   * aLayerOffset are integer rounded using Point's RoundedToInt.
   *
   * @param aResult - the resulting visible region of this layer.
   * @param aLayerOffset - this layer's total offset from the root layer.
   * @return - false if during layer tree traversal a parent or sibling
   *  transform is found to be non-translational. This method returns early
   *  in this case, results will not be valid. Returns true on successful
   *  traversal.
   */
  bool GetVisibleRegionRelativeToRootLayer(nsIntRegion& aResult,
                                           nsIntPoint* aLayerOffset);

  // Note that all lengths in animation data are either in CSS pixels or app
  // units and must be converted to device pixels by the compositor.
  AnimationArray& GetAnimations() { return mAnimations; }
  InfallibleTArray<AnimData>& GetAnimationData() { return mAnimationData; }

  uint64_t GetAnimationGeneration() { return mAnimationGeneration; }
  void SetAnimationGeneration(uint64_t aCount) { mAnimationGeneration = aCount; }

  bool HasTransformAnimation() const;

  /**
   * Returns the local transform for this layer: either mTransform or,
   * for shadow layers, GetShadowTransform()
   */
  const gfx::Matrix4x4 GetLocalTransform();

  /**
   * Returns the local opacity for this layer: either mOpacity or,
   * for shadow layers, GetShadowOpacity()
   */
  const float GetLocalOpacity();

  /**
   * DRAWING PHASE ONLY
   *
   * Apply pending changes to layers before drawing them, if those
   * pending changes haven't been overridden by later changes.
   */
  void ApplyPendingUpdatesToSubtree();

  /**
   * DRAWING PHASE ONLY
   *
   * Write layer-subtype-specific attributes into aAttrs.  Used to
   * synchronize layer attributes to their shadows'.
   */
  virtual void FillSpecificAttributes(SpecificLayerAttributes& aAttrs) { }

  // Returns true if it's OK to save the contents of aLayer in an
  // opaque surface (a surface without an alpha channel).
  // If we can use a surface without an alpha channel, we should, because
  // it will often make painting of antialiased text faster and higher
  // quality.
  bool CanUseOpaqueSurface();

  SurfaceMode GetSurfaceMode()
  {
    if (CanUseOpaqueSurface())
      return SurfaceMode::SURFACE_OPAQUE;
    if (mContentFlags & CONTENT_COMPONENT_ALPHA)
      return SurfaceMode::SURFACE_COMPONENT_ALPHA;
    return SurfaceMode::SURFACE_SINGLE_CHANNEL_ALPHA;
  }

  // Returns true if this layer can be treated as opaque for visibility
  // computation. A layer may be non-opaque for visibility even if it
  // is not transparent, for example, if it has a mix-blend-mode.
  bool IsOpaqueForVisibility();

  /**
   * This setter can be used anytime. The user data for all keys is
   * initially null. Ownership pases to the layer manager.
   */
  void SetUserData(void* aKey, LayerUserData* aData)
  {
    mUserData.Add(static_cast<gfx::UserDataKey*>(aKey), aData, LayerManager::LayerUserDataDestroy);
  }
  /**
   * This can be used anytime. Ownership passes to the caller!
   */
  nsAutoPtr<LayerUserData> RemoveUserData(void* aKey);
  /**
   * This getter can be used anytime.
   */
  bool HasUserData(void* aKey)
  {
    return mUserData.Has(static_cast<gfx::UserDataKey*>(aKey));
  }
  /**
   * This getter can be used anytime. Ownership is retained by the layer
   * manager.
   */
  LayerUserData* GetUserData(void* aKey) const
  {
    return static_cast<LayerUserData*>(mUserData.Get(static_cast<gfx::UserDataKey*>(aKey)));
  }

  /**
   * |Disconnect()| is used by layers hooked up over IPC.  It may be
   * called at any time, and may not be called at all.  Using an
   * IPC-enabled layer after Destroy() (drawing etc.) results in a
   * safe no-op; no crashy or uaf etc.
   *
   * XXX: this interface is essentially LayerManager::Destroy, but at
   * Layer granularity.  It might be beneficial to unify them.
   */
  virtual void Disconnect() {}

  /**
   * Dynamic downcast to a PaintedLayer. Returns null if this is not
   * a PaintedLayer.
   */
  virtual PaintedLayer* AsPaintedLayer() { return nullptr; }

  /**
   * Dynamic cast to a ContainerLayer. Returns null if this is not
   * a ContainerLayer.
   */
  virtual ContainerLayer* AsContainerLayer() { return nullptr; }
  virtual const ContainerLayer* AsContainerLayer() const { return nullptr; }

   /**
    * Dynamic cast to a RefLayer. Returns null if this is not a
    * RefLayer.
    */
  virtual RefLayer* AsRefLayer() { return nullptr; }

   /**
    * Dynamic cast to a Color. Returns null if this is not a
    * ColorLayer.
    */
  virtual ColorLayer* AsColorLayer() { return nullptr; }

  /**
   * Dynamic cast to a LayerComposite.  Return null if this is not a
   * LayerComposite.  Can be used anytime.
   */
  virtual LayerComposite* AsLayerComposite() { return nullptr; }

  /**
   * Dynamic cast to a ShadowableLayer.  Return null if this is not a
   * ShadowableLayer.  Can be used anytime.
   */
  virtual ShadowableLayer* AsShadowableLayer() { return nullptr; }

  // These getters can be used anytime.  They return the effective
  // values that should be used when drawing this layer to screen,
  // accounting for this layer possibly being a shadow.
  const Maybe<ParentLayerIntRect>& GetEffectiveClipRect();
  const LayerIntRegion& GetEffectiveVisibleRegion();

  /**
   * Returns the product of the opacities of this layer and all ancestors up
   * to and excluding the nearest ancestor that has UseIntermediateSurface() set.
   */
  float GetEffectiveOpacity();

  /**
   * Returns the blendmode of this layer.
   */
  gfx::CompositionOp GetEffectiveMixBlendMode();

  /**
   * This returns the effective transform computed by
   * ComputeEffectiveTransforms. Typically this is a transform that transforms
   * this layer all the way to some intermediate surface or destination
   * surface. For non-BasicLayers this will be a transform to the nearest
   * ancestor with UseIntermediateSurface() (or to the root, if there is no
   * such ancestor), but for BasicLayers it's different.
   */
  const gfx::Matrix4x4& GetEffectiveTransform() const { return mEffectiveTransform; }

  /**
   * This returns the effective transform for Layer's buffer computed by
   * ComputeEffectiveTransforms. Typically this is a transform that transforms
   * this layer's buffer all the way to some intermediate surface or destination
   * surface. For non-BasicLayers this will be a transform to the nearest
   * ancestor with UseIntermediateSurface() (or to the root, if there is no
   * such ancestor), but for BasicLayers it's different.
   *
   * By default, its value is same to GetEffectiveTransform().
   * When ImageLayer is rendered with ScaleMode::STRETCH,
   * it becomes different from GetEffectiveTransform().
   */
  virtual const gfx::Matrix4x4& GetEffectiveTransformForBuffer() const
  {
    return mEffectiveTransform;
  }

  /**
   * @param aTransformToSurface the composition of the transforms
   * from the parent layer (if any) to the destination pixel grid.
   *
   * Computes mEffectiveTransform for this layer and all its descendants.
   * mEffectiveTransform transforms this layer up to the destination
   * pixel grid (whatever aTransformToSurface is relative to).
   *
   * We promise that when this is called on a layer, all ancestor layers
   * have already had ComputeEffectiveTransforms called.
   */
  virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface) = 0;

  /**
   * Computes the effective transform for mask layers, if this layer has any.
   */
  void ComputeEffectiveTransformForMaskLayers(const gfx::Matrix4x4& aTransformToSurface);
  static void ComputeEffectiveTransformForMaskLayer(Layer* aMaskLayer,
                                                    const gfx::Matrix4x4& aTransformToSurface);

  /**
   * Calculate the scissor rect required when rendering this layer.
   * Returns a rectangle relative to the intermediate surface belonging to the
   * nearest ancestor that has an intermediate surface, or relative to the root
   * viewport if no ancestor has an intermediate surface, corresponding to the
   * clip rect for this layer intersected with aCurrentScissorRect.
   */
  RenderTargetIntRect CalculateScissorRect(const RenderTargetIntRect& aCurrentScissorRect);

  virtual const char* Name() const =0;
  virtual LayerType GetType() const =0;

  /**
   * Only the implementation should call this. This is per-implementation
   * private data. Normally, all layers with a given layer manager
   * use the same type of ImplData.
   */
  void* ImplData() { return mImplData; }

  /**
   * Only the implementation should use these methods.
   */
  void SetParent(ContainerLayer* aParent) { mParent = aParent; }
  void SetNextSibling(Layer* aSibling) { mNextSibling = aSibling; }
  void SetPrevSibling(Layer* aSibling) { mPrevSibling = aSibling; }

  /**
   * Dump information about this layer manager and its managed tree to
   * aStream.
   */
  void Dump(std::stringstream& aStream, const char* aPrefix="", bool aDumpHtml=false);
  /**
   * Dump information about just this layer manager itself to aStream.
   */
  void DumpSelf(std::stringstream& aStream, const char* aPrefix="");

  /**
   * Dump information about this layer and its child & sibling layers to
   * layerscope packet.
   */
  void Dump(layerscope::LayersPacket* aPacket, const void* aParent);

  /**
   * Log information about this layer manager and its managed tree to
   * the NSPR log (if enabled for "Layers").
   */
  void Log(const char* aPrefix="");
  /**
   * Log information about just this layer manager itself to the NSPR
   * log (if enabled for "Layers").
   */
  void LogSelf(const char* aPrefix="");

  // Print interesting information about this into aStream. Internally
  // used to implement Dump*() and Log*(). If subclasses have
  // additional interesting properties, they should override this with
  // an implementation that first calls the base implementation then
  // appends additional info to aTo.
  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix);

  // Just like PrintInfo, but this function dump information into layerscope packet,
  // instead of a StringStream. It is also internally used to implement Dump();
  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent);

  /**
   * Store display list log.
   */
  void SetDisplayListLog(const char *log);

  /**
   * Return display list log.
   */
  void GetDisplayListLog(nsCString& log);

  static bool IsLogEnabled() { return LayerManager::IsLogEnabled(); }

  /**
   * Returns the current area of the layer (in layer-space coordinates)
   * marked as needed to be recomposited.
   */
  const nsIntRegion& GetInvalidRegion() { return mInvalidRegion; }
  const void AddInvalidRegion(const nsIntRegion& aRegion) {
    mInvalidRegion.Or(mInvalidRegion, aRegion);
  }

  /**
   * Mark the entirety of the layer's visible region as being invalid.
   */
  void SetInvalidRectToVisibleRegion() { mInvalidRegion = GetVisibleRegion().ToUnknownRegion(); }

  /**
   * Adds to the current invalid rect.
   */
  void AddInvalidRect(const gfx::IntRect& aRect) { mInvalidRegion.Or(mInvalidRegion, aRect); }

  /**
   * Clear the invalid rect, marking the layer as being identical to what is currently
   * composited.
   */
  void ClearInvalidRect() { mInvalidRegion.SetEmpty(); }

  // These functions allow attaching an AsyncPanZoomController to this layer,
  // and can be used anytime.
  // A layer has an APZC at index aIndex only-if GetFrameMetrics(aIndex).IsScrollable();
  // attempting to get an APZC for a non-scrollable metrics will return null.
  // The aIndex for these functions must be less than GetFrameMetricsCount().
  void SetAsyncPanZoomController(uint32_t aIndex, AsyncPanZoomController *controller);
  AsyncPanZoomController* GetAsyncPanZoomController(uint32_t aIndex) const;
  // The FrameMetricsChanged function is used internally to ensure the APZC array length
  // matches the frame metrics array length.
private:
  void FrameMetricsChanged();
public:

  void ApplyPendingUpdatesForThisTransaction();

#ifdef DEBUG
  void SetDebugColorIndex(uint32_t aIndex) { mDebugColorIndex = aIndex; }
  uint32_t GetDebugColorIndex() { return mDebugColorIndex; }
#endif

  virtual LayerRenderState GetRenderState() { return LayerRenderState(); }

  void Mutated()
  {
    mManager->Mutated(this);
  }

  virtual int32_t GetMaxLayerSize() { return Manager()->GetMaxTextureSize(); }

  /**
   * Returns true if this layer's effective transform is not just
   * a translation by integers, or if this layer or some ancestor layer
   * is marked as having a transform that may change without a full layer
   * transaction.
   */
  bool MayResample();

  RenderTargetRect TransformRectToRenderTarget(const LayerIntRect& aRect);

  /**
   * Add debugging information to the layer dump.
   */
  void AddExtraDumpInfo(const nsACString& aStr)
  {
#ifdef MOZ_DUMP_PAINTING
    mExtraDumpInfo.AppendElement(aStr);
#endif
  }

  /**
   * Clear debugging information. Useful for recycling.
   */
  void ClearExtraDumpInfo()
  {
#ifdef MOZ_DUMP_PAINTING
     mExtraDumpInfo.Clear();
#endif
  }

  /**
   * Replace the current effective transform with the given one,
   * returning the old one.  This is currently added as a hack for VR
   * rendering, and might go away if we find a better way to do this.
   * If you think you have a need for this method, talk with
   * vlad/mstange/mwoodrow first.
   */
  virtual gfx::Matrix4x4 ReplaceEffectiveTransform(const gfx::Matrix4x4& aNewEffectiveTransform) {
    gfx::Matrix4x4 old = mEffectiveTransform;
    mEffectiveTransform = aNewEffectiveTransform;
    ComputeEffectiveTransformForMaskLayers(mEffectiveTransform);
    return old;
  }

protected:
  Layer(LayerManager* aManager, void* aImplData);

  // Protected destructor, to discourage deletion outside of Release():
  virtual ~Layer();

  /**
   * We can snap layer transforms for two reasons:
   * 1) To avoid unnecessary resampling when a transform is a translation
   * by a non-integer number of pixels.
   * Snapping the translation to an integer number of pixels avoids
   * blurring the layer and can be faster to composite.
   * 2) When a layer is used to render a rectangular object, we need to
   * emulate the rendering of rectangular inactive content and snap the
   * edges of the rectangle to pixel boundaries. This is both to ensure
   * layer rendering is consistent with inactive content rendering, and to
   * avoid seams.
   * This function implements type 1 snapping. If aTransform is a 2D
   * translation, and this layer's layer manager has enabled snapping
   * (which is the default), return aTransform with the translation snapped
   * to nearest pixels. Otherwise just return aTransform. Call this when the
   * layer does not correspond to a single rectangular content object.
   * This function does not try to snap if aTransform has a scale, because in
   * that case resampling is inevitable and there's no point in trying to
   * avoid it. In fact snapping can cause problems because pixel edges in the
   * layer's content can be rendered unpredictably (jiggling) as the scale
   * interacts with the snapping of the translation, especially with animated
   * transforms.
   * @param aResidualTransform a transform to apply before the result transform
   * in order to get the results to completely match aTransform.
   */
  gfx::Matrix4x4 SnapTransformTranslation(const gfx::Matrix4x4& aTransform,
                                          gfx::Matrix* aResidualTransform);
  /**
   * See comment for SnapTransformTranslation.
   * This function implements type 2 snapping. If aTransform is a translation
   * and/or scale, transform aSnapRect by aTransform, snap to pixel boundaries,
   * and return the transform that maps aSnapRect to that rect. Otherwise
   * just return aTransform.
   * @param aSnapRect a rectangle whose edges should be snapped to pixel
   * boundaries in the destination surface.
   * @param aResidualTransform a transform to apply before the result transform
   * in order to get the results to completely match aTransform.
   */
  gfx::Matrix4x4 SnapTransform(const gfx::Matrix4x4& aTransform,
                               const gfxRect& aSnapRect,
                               gfx::Matrix* aResidualTransform);

  LayerManager* mManager;
  ContainerLayer* mParent;
  Layer* mNextSibling;
  Layer* mPrevSibling;
  void* mImplData;
  RefPtr<Layer> mMaskLayer;
  nsTArray<RefPtr<Layer>> mAncestorMaskLayers;
  gfx::UserData mUserData;
  gfx::IntRect mLayerBounds;
  LayerIntRegion mVisibleRegion;
  nsTArray<FrameMetrics> mFrameMetrics;
  EventRegions mEventRegions;
  gfx::Matrix4x4 mTransform;
  // A mutation of |mTransform| that we've queued to be applied at the
  // end of the next transaction (if nothing else overrides it in the
  // meantime).
  nsAutoPtr<gfx::Matrix4x4> mPendingTransform;
  float mPostXScale;
  float mPostYScale;
  gfx::Matrix4x4 mEffectiveTransform;
  AnimationArray mAnimations;
  // See mPendingTransform above.
  nsAutoPtr<AnimationArray> mPendingAnimations;
  InfallibleTArray<AnimData> mAnimationData;
  float mOpacity;
  gfx::CompositionOp mMixBlendMode;
  bool mForceIsolatedGroup;
  Maybe<ParentLayerIntRect> mClipRect;
  gfx::IntRect mTileSourceRect;
  nsIntRegion mInvalidRegion;
  nsTArray<RefPtr<AsyncPanZoomController> > mApzcs;
  uint32_t mContentFlags;
  bool mUseTileSourceRect;
  bool mIsFixedPosition;
  struct FixedPositionData {
    FrameMetrics::ViewID mScrollId;
    LayerPoint mAnchor;
    int32_t mSides;
    bool mIsClipFixed;
  };
  UniquePtr<FixedPositionData> mFixedPositionData;
  struct StickyPositionData {
    FrameMetrics::ViewID mScrollId;
    LayerRect mOuter;
    LayerRect mInner;
  };
  nsAutoPtr<StickyPositionData> mStickyPositionData;
  FrameMetrics::ViewID mScrollbarTargetId;
  ScrollDirection mScrollbarDirection;
  // The scrollbar thumb ratio is the ratio of the thumb position (in the CSS
  // pixels of the scrollframe's parent's space) to the scroll position (in the
  // CSS pixels of the scrollframe's space).
  float mScrollbarThumbRatio;
  bool mIsScrollbarContainer;
  DebugOnly<uint32_t> mDebugColorIndex;
  // If this layer is used for OMTA, then this counter is used to ensure we
  // stay in sync with the animation manager
  uint64_t mAnimationGeneration;
#ifdef MOZ_DUMP_PAINTING
  nsTArray<nsCString> mExtraDumpInfo;
#endif
  // Store display list log.
  nsCString mDisplayListLog;
};

/**
 * A Layer which we can paint into. It is a conceptually
 * infinite surface, but each PaintedLayer has an associated "valid region"
 * of contents that it is currently storing, which is finite. PaintedLayer
 * implementations can store content between paints.
 *
 * PaintedLayers are rendered into during the drawing phase of a transaction.
 *
 * Currently the contents of a PaintedLayer are in the device output color
 * space.
 */
class PaintedLayer : public Layer {
public:
  /**
   * CONSTRUCTION PHASE ONLY
   * Tell this layer that the content in some region has changed and
   * will need to be repainted. This area is removed from the valid
   * region.
   */
  virtual void InvalidateRegion(const nsIntRegion& aRegion) = 0;
  /**
   * CONSTRUCTION PHASE ONLY
   * Set whether ComputeEffectiveTransforms should compute the
   * "residual translation" --- the translation that should be applied *before*
   * mEffectiveTransform to get the ideal transform for this PaintedLayer.
   * When this is true, ComputeEffectiveTransforms will compute the residual
   * and ensure that the layer is invalidated whenever the residual changes.
   * When it's false, a change in the residual will not trigger invalidation
   * and GetResidualTranslation will return 0,0.
   * So when the residual is to be ignored, set this to false for better
   * performance.
   */
  void SetAllowResidualTranslation(bool aAllow) { mAllowResidualTranslation = aAllow; }

  /**
   * Can be used anytime
   */
  const nsIntRegion& GetValidRegion() const { return mValidRegion; }

  virtual PaintedLayer* AsPaintedLayer() override { return this; }

  MOZ_LAYER_DECL_NAME("PaintedLayer", TYPE_PAINTED)

  virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface) override
  {
    gfx::Matrix4x4 idealTransform = GetLocalTransform() * aTransformToSurface;
    gfx::Matrix residual;
    mEffectiveTransform = SnapTransformTranslation(idealTransform,
        mAllowResidualTranslation ? &residual : nullptr);
    // The residual can only be a translation because SnapTransformTranslation
    // only changes the transform if it's a translation
    NS_ASSERTION(residual.IsTranslation(),
                 "Residual transform can only be a translation");
    if (!gfx::ThebesPoint(residual.GetTranslation()).WithinEpsilonOf(mResidualTranslation, 1e-3f)) {
      mResidualTranslation = gfx::ThebesPoint(residual.GetTranslation());
      NS_ASSERTION(-0.5 <= mResidualTranslation.x && mResidualTranslation.x < 0.5 &&
                   -0.5 <= mResidualTranslation.y && mResidualTranslation.y < 0.5,
                   "Residual translation out of range");
      mValidRegion.SetEmpty();
    }
    ComputeEffectiveTransformForMaskLayers(aTransformToSurface);
  }

  LayerManager::PaintedLayerCreationHint GetCreationHint() const { return mCreationHint; }

  bool UsedForReadback() { return mUsedForReadback; }
  void SetUsedForReadback(bool aUsed) { mUsedForReadback = aUsed; }

  /**
   * Returns true if aLayer is optimized for the given PaintedLayerCreationHint.
   */
  virtual bool IsOptimizedFor(LayerManager::PaintedLayerCreationHint aCreationHint)
  { return true; }

  /**
   * Returns the residual translation. Apply this translation when drawing
   * into the PaintedLayer so that when mEffectiveTransform is applied afterwards
   * by layer compositing, the results exactly match the "ideal transform"
   * (the product of the transform of this layer and its ancestors).
   * Returns 0,0 unless SetAllowResidualTranslation(true) has been called.
   * The residual translation components are always in the range [-0.5, 0.5).
   */
  gfxPoint GetResidualTranslation() const { return mResidualTranslation; }

protected:
  PaintedLayer(LayerManager* aManager, void* aImplData,
              LayerManager::PaintedLayerCreationHint aCreationHint = LayerManager::NONE)
    : Layer(aManager, aImplData)
    , mValidRegion()
    , mCreationHint(aCreationHint)
    , mUsedForReadback(false)
    , mAllowResidualTranslation(false)
  {
    mContentFlags = 0; // Clear NO_TEXT, NO_TEXT_OVER_TRANSPARENT
  }

  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix) override;

  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent) override;

  /**
   * ComputeEffectiveTransforms snaps the ideal transform to get mEffectiveTransform.
   * mResidualTranslation is the translation that should be applied *before*
   * mEffectiveTransform to get the ideal transform.
   */
  gfxPoint mResidualTranslation;
  nsIntRegion mValidRegion;
  /**
   * The creation hint that was used when constructing this layer.
   */
  const LayerManager::PaintedLayerCreationHint mCreationHint;
  /**
   * Set when this PaintedLayer is participating in readback, i.e. some
   * ReadbackLayer (may) be getting its background from this layer.
   */
  bool mUsedForReadback;
  /**
   * True when
   */
  bool mAllowResidualTranslation;
};

/**
 * A Layer which other layers render into. It holds references to its
 * children.
 */
class ContainerLayer : public Layer {
public:

  ~ContainerLayer();

  /**
   * CONSTRUCTION PHASE ONLY
   * Insert aChild into the child list of this container. aChild must
   * not be currently in any child list or the root for the layer manager.
   * If aAfter is non-null, it must be a child of this container and
   * we insert after that layer. If it's null we insert at the start.
   */
  virtual bool InsertAfter(Layer* aChild, Layer* aAfter);
  /**
   * CONSTRUCTION PHASE ONLY
   * Remove aChild from the child list of this container. aChild must
   * be a child of this container.
   */
  virtual bool RemoveChild(Layer* aChild);
  /**
   * CONSTRUCTION PHASE ONLY
   * Reposition aChild from the child list of this container. aChild must
   * be a child of this container.
   * If aAfter is non-null, it must be a child of this container and we
   * reposition after that layer. If it's null, we reposition at the start.
   */
  virtual bool RepositionChild(Layer* aChild, Layer* aAfter);

  void SetPreScale(float aXScale, float aYScale)
  {
    if (mPreXScale == aXScale && mPreYScale == aYScale) {
      return;
    }

    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) PreScale", this));
    mPreXScale = aXScale;
    mPreYScale = aYScale;
    Mutated();
  }

  void SetInheritedScale(float aXScale, float aYScale)
  {
    if (mInheritedXScale == aXScale && mInheritedYScale == aYScale) {
      return;
    }

    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) InheritedScale", this));
    mInheritedXScale = aXScale;
    mInheritedYScale = aYScale;
    Mutated();
  }

  void SetScaleToResolution(bool aScaleToResolution, float aResolution)
  {
    if (mScaleToResolution == aScaleToResolution && mPresShellResolution == aResolution) {
      return;
    }

    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ScaleToResolution", this));
    mScaleToResolution = aScaleToResolution;
    mPresShellResolution = aResolution;
    Mutated();
  }

  virtual void FillSpecificAttributes(SpecificLayerAttributes& aAttrs) override;

  void SortChildrenBy3DZOrder(nsTArray<Layer*>& aArray);

  // These getters can be used anytime.

  virtual ContainerLayer* AsContainerLayer() override { return this; }
  virtual const ContainerLayer* AsContainerLayer() const override { return this; }

  virtual Layer* GetFirstChild() const override { return mFirstChild; }
  virtual Layer* GetLastChild() const override { return mLastChild; }
  float GetPreXScale() const { return mPreXScale; }
  float GetPreYScale() const { return mPreYScale; }
  float GetInheritedXScale() const { return mInheritedXScale; }
  float GetInheritedYScale() const { return mInheritedYScale; }
  float GetPresShellResolution() const { return mPresShellResolution; }
  bool ScaleToResolution() const { return mScaleToResolution; }

  MOZ_LAYER_DECL_NAME("ContainerLayer", TYPE_CONTAINER)

  /**
   * ContainerLayer backends need to override ComputeEffectiveTransforms
   * since the decision about whether to use a temporary surface for the
   * container is backend-specific. ComputeEffectiveTransforms must also set
   * mUseIntermediateSurface.
   */
  virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface) override = 0;

  /**
   * Call this only after ComputeEffectiveTransforms has been invoked
   * on this layer.
   * Returns true if this will use an intermediate surface. This is largely
   * backend-dependent, but it affects the operation of GetEffectiveOpacity().
   */
  bool UseIntermediateSurface() { return mUseIntermediateSurface; }

  /**
   * Returns the rectangle covered by the intermediate surface,
   * in this layer's coordinate system.
   *
   * NOTE: Since this layer has an intermediate surface it follows
   *       that LayerPixel == RenderTargetPixel
   */
  RenderTargetIntRect GetIntermediateSurfaceRect()
  {
    NS_ASSERTION(mUseIntermediateSurface, "Must have intermediate surface");
    return RenderTargetIntRect::FromUnknownRect(GetEffectiveVisibleRegion().ToUnknownRegion().GetBounds());
  }

  /**
   * Returns true if this container has more than one non-empty child
   */
  bool HasMultipleChildren();

  /**
   * Returns true if this container supports children with component alpha.
   * Should only be called while painting a child of this layer.
   */
  bool SupportsComponentAlphaChildren() { return mSupportsComponentAlphaChildren; }

  /**
   * Returns true if aLayer or any layer in its parent chain has the opaque
   * content flag set.
   */
  static bool HasOpaqueAncestorLayer(Layer* aLayer);

  void SetChildrenChanged(bool aVal) {
    mChildrenChanged = aVal;
  }

  void SetEventRegionsOverride(EventRegionsOverride aVal) {
    if (mEventRegionsOverride == aVal) {
      return;
    }

    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) EventRegionsOverride", this));
    mEventRegionsOverride = aVal;
    Mutated();
  }

  EventRegionsOverride GetEventRegionsOverride() const {
    return mEventRegionsOverride;
  }

  /**
   * VR
   */
  void SetVRHMDInfo(gfx::VRHMDInfo* aHMD) { mHMDInfo = aHMD; }
  gfx::VRHMDInfo* GetVRHMDInfo() { return mHMDInfo; }

  /**
   * Replace the current effective transform with the given one,
   * returning the old one.  This is currently added as a hack for VR
   * rendering, and might go away if we find a better way to do this.
   * If you think you have a need for this method, talk with
   * vlad/mstange/mwoodrow first.
   */
  gfx::Matrix4x4 ReplaceEffectiveTransform(const gfx::Matrix4x4& aNewEffectiveTransform) override {
    gfx::Matrix4x4 old = mEffectiveTransform;
    mEffectiveTransform = aNewEffectiveTransform;
    ComputeEffectiveTransformsForChildren(mEffectiveTransform);
    ComputeEffectiveTransformForMaskLayers(mEffectiveTransform);
    return old;
  }

protected:
  friend class ReadbackProcessor;

  void DidInsertChild(Layer* aLayer);
  void DidRemoveChild(Layer* aLayer);

  ContainerLayer(LayerManager* aManager, void* aImplData);

  /**
   * A default implementation of ComputeEffectiveTransforms for use by OpenGL
   * and D3D.
   */
  void DefaultComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface);

  /**
   * A default implementation to compute and set the value for SupportsComponentAlphaChildren().
   *
   * If aNeedsSurfaceCopy is provided, then it is set to true if the caller needs to copy the background
   * up into the intermediate surface created, false otherwise.
   */
  void DefaultComputeSupportsComponentAlphaChildren(bool* aNeedsSurfaceCopy = nullptr);

  /**
   * Loops over the children calling ComputeEffectiveTransforms on them.
   */
  void ComputeEffectiveTransformsForChildren(const gfx::Matrix4x4& aTransformToSurface);

  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix) override;

  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent) override;

  Layer* mFirstChild;
  Layer* mLastChild;
  float mPreXScale;
  float mPreYScale;
  // The resolution scale inherited from the parent layer. This will already
  // be part of mTransform.
  float mInheritedXScale;
  float mInheritedYScale;
  // For layers corresponding to an nsDisplayResolution, the resolution of the
  // associated pres shell; for other layers, 1.0.
  float mPresShellResolution;
  // Whether the compositor should scale to mPresShellResolution.
  bool mScaleToResolution;
  bool mUseIntermediateSurface;
  bool mSupportsComponentAlphaChildren;
  bool mMayHaveReadbackChild;
  // This is updated by ComputeDifferences. This will be true if we need to invalidate
  // the intermediate surface.
  bool mChildrenChanged;
  EventRegionsOverride mEventRegionsOverride;
  RefPtr<gfx::VRHMDInfo> mHMDInfo;
};

/**
 * A Layer which just renders a solid color in its visible region. It actually
 * can fill any area that contains the visible region, so if you need to
 * restrict the area filled, set a clip region on this layer.
 */
class ColorLayer : public Layer {
public:
  virtual ColorLayer* AsColorLayer() override { return this; }

  /**
   * CONSTRUCTION PHASE ONLY
   * Set the color of the layer.
   */
  virtual void SetColor(const gfx::Color& aColor)
  {
    if (mColor != aColor) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) Color", this));
      mColor = aColor;
      Mutated();
    }
  }

  void SetBounds(const gfx::IntRect& aBounds)
  {
    if (!mBounds.IsEqualEdges(aBounds)) {
      mBounds = aBounds;
      Mutated();
    }
  }

  const gfx::IntRect& GetBounds()
  {
    return mBounds;
  }

  // This getter can be used anytime.
  virtual const gfx::Color& GetColor() { return mColor; }

  MOZ_LAYER_DECL_NAME("ColorLayer", TYPE_COLOR)

  virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface) override
  {
    gfx::Matrix4x4 idealTransform = GetLocalTransform() * aTransformToSurface;
    mEffectiveTransform = SnapTransformTranslation(idealTransform, nullptr);
    ComputeEffectiveTransformForMaskLayers(aTransformToSurface);
  }

protected:
  ColorLayer(LayerManager* aManager, void* aImplData)
    : Layer(aManager, aImplData)
    , mColor()
  {}

  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix) override;

  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent) override;

  gfx::IntRect mBounds;
  gfx::Color mColor;
};

/**
 * A Layer for HTML Canvas elements.  It's backed by either a
 * gfxASurface or a GLContext (for WebGL layers), and has some control
 * for intelligent updating from the source if necessary (for example,
 * if hardware compositing is not available, for reading from the GL
 * buffer into an image surface that we can layer composite.)
 *
 * After Initialize is called, the underlying canvas Surface/GLContext
 * must not be modified during a layer transaction.
 */
class CanvasLayer : public Layer {
public:
  struct Data {
    Data()
      : mBufferProvider(nullptr)
      , mGLContext(nullptr)
      , mRenderer(nullptr)
      , mFrontbufferGLTex(0)
      , mSize(0,0)
      , mHasAlpha(false)
      , mIsGLAlphaPremult(true)
    { }

    // One of these three must be specified for Canvas2D, but never more than one
    PersistentBufferProvider* mBufferProvider; // A BufferProvider for the Canvas contents
    mozilla::gl::GLContext* mGLContext; // or this, for GL.
    AsyncCanvasRenderer* mRenderer; // or this, for OffscreenCanvas

    // Frontbuffer override
    uint32_t mFrontbufferGLTex;

    // The size of the canvas content
    gfx::IntSize mSize;

    // Whether the canvas drawingbuffer has an alpha channel.
    bool mHasAlpha;

    // Whether mGLContext contains data that is alpha-premultiplied.
    bool mIsGLAlphaPremult;
  };

  /**
   * CONSTRUCTION PHASE ONLY
   * Initialize this CanvasLayer with the given data.  The data must
   * have either mSurface or mGLContext initialized (but not both), as
   * well as mSize.
   *
   * This must only be called once.
   */
  virtual void Initialize(const Data& aData) = 0;

  /**
   * Check the data is owned by this layer is still valid for rendering
   */
  virtual bool IsDataValid(const Data& aData) { return true; }

  /**
   * Notify this CanvasLayer that the canvas surface contents have
   * changed (or will change) before the next transaction.
   */
  void Updated() { mDirty = true; SetInvalidRectToVisibleRegion(); }

  /**
   * Notify this CanvasLayer that the canvas surface contents have
   * been painted since the last change.
   */
  void Painted() { mDirty = false; }

  /**
   * Returns true if the canvas surface contents have changed since the
   * last paint.
   */
  bool IsDirty()
  {
    // We can only tell if we are dirty if we're part of the
    // widget's retained layer tree.
    if (!mManager || !mManager->IsWidgetLayerManager()) {
      return true;
    }
    return mDirty;
  }

  /**
   * Register a callback to be called at the start of each transaction.
   */
  typedef void PreTransactionCallback(void* closureData);
  void SetPreTransactionCallback(PreTransactionCallback* callback, void* closureData)
  {
    mPreTransCallback = callback;
    mPreTransCallbackData = closureData;
  }

  const nsIntRect& GetBounds() const { return mBounds; }

protected:
  void FirePreTransactionCallback()
  {
    if (mPreTransCallback) {
      mPreTransCallback(mPreTransCallbackData);
    }
  }

public:
  /**
   * Register a callback to be called at the end of each transaction.
   */
  typedef void (* DidTransactionCallback)(void* aClosureData);
  void SetDidTransactionCallback(DidTransactionCallback aCallback, void* aClosureData)
  {
    mPostTransCallback = aCallback;
    mPostTransCallbackData = aClosureData;
  }

  /**
   * CONSTRUCTION PHASE ONLY
   * Set the filter used to resample this image (if necessary).
   */
  void SetFilter(gfx::Filter aFilter)
  {
    if (mFilter != aFilter) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) Filter", this));
      mFilter = aFilter;
      Mutated();
    }
  }
  gfx::Filter GetFilter() const { return mFilter; }

  MOZ_LAYER_DECL_NAME("CanvasLayer", TYPE_CANVAS)

  virtual void ComputeEffectiveTransforms(const gfx::Matrix4x4& aTransformToSurface) override
  {
    // Snap our local transform first, and snap the inherited transform as well.
    // This makes our snapping equivalent to what would happen if our content
    // was drawn into a PaintedLayer (gfxContext would snap using the local
    // transform, then we'd snap again when compositing the PaintedLayer).
    mEffectiveTransform =
        SnapTransform(GetLocalTransform(), gfxRect(0, 0, mBounds.width, mBounds.height),
                      nullptr)*
        SnapTransformTranslation(aTransformToSurface, nullptr);
    ComputeEffectiveTransformForMaskLayers(aTransformToSurface);
  }

  bool GetIsAsyncRenderer() const
  {
    return !!mAsyncRenderer;
  }

protected:
  CanvasLayer(LayerManager* aManager, void* aImplData);
  virtual ~CanvasLayer();

  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix) override;

  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent) override;

  void FireDidTransactionCallback()
  {
    if (mPostTransCallback) {
      mPostTransCallback(mPostTransCallbackData);
    }
  }

  /**
   * 0, 0, canvaswidth, canvasheight
   */
  gfx::IntRect mBounds;
  PreTransactionCallback* mPreTransCallback;
  void* mPreTransCallbackData;
  DidTransactionCallback mPostTransCallback;
  void* mPostTransCallbackData;
  gfx::Filter mFilter;
  RefPtr<AsyncCanvasRenderer> mAsyncRenderer;

private:
  /**
   * Set to true in Updated(), cleared during a transaction.
   */
  bool mDirty;
};

/**
 * ContainerLayer that refers to a "foreign" layer tree, through an
 * ID.  Usage of RefLayer looks like
 *
 * Construction phase:
 *   allocate ID for layer subtree
 *   create RefLayer, SetReferentId(ID)
 *
 * Composition:
 *   look up subtree for GetReferentId()
 *   ConnectReferentLayer(subtree)
 *   compose
 *   ClearReferentLayer()
 *
 * Clients will usually want to Connect/Clear() on each transaction to
 * avoid difficulties managing memory across multiple layer subtrees.
 */
class RefLayer : public ContainerLayer {
  friend class LayerManager;

private:
  virtual bool InsertAfter(Layer* aChild, Layer* aAfter) override
  { MOZ_CRASH(); return false; }

  virtual bool RemoveChild(Layer* aChild) override
  { MOZ_CRASH(); return false; }

  virtual bool RepositionChild(Layer* aChild, Layer* aAfter) override
  { MOZ_CRASH(); return false; }

  using Layer::SetFrameMetrics;

public:
  /**
   * CONSTRUCTION PHASE ONLY
   * Set the ID of the layer's referent.
   */
  void SetReferentId(uint64_t aId)
  {
    MOZ_ASSERT(aId != 0);
    if (mId != aId) {
      MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) ReferentId", this));
      mId = aId;
      Mutated();
    }
  }
  /**
   * CONSTRUCTION PHASE ONLY
   * Connect this ref layer to its referent, temporarily.
   * ClearReferentLayer() must be called after composition.
   */
  void ConnectReferentLayer(Layer* aLayer)
  {
    MOZ_ASSERT(!mFirstChild && !mLastChild);
    MOZ_ASSERT(!aLayer->GetParent());
    if (aLayer->Manager() != Manager()) {
      // This can happen when e.g. rendering while dragging tabs
      // between windows - aLayer's manager may be the manager for the
      // old window's tab.  In that case, it will be changed before the
      // next render (see SetLayerManager).  It is simply easier to
      // ignore the rendering here than it is to pause it.
      NS_WARNING("ConnectReferentLayer failed - Incorrect LayerManager");
      return;
    }

    mFirstChild = mLastChild = aLayer;
    aLayer->SetParent(this);
  }

  /**
   * DRAWING PHASE ONLY
   * |aLayer| is the same as the argument to ConnectReferentLayer().
   */
  void DetachReferentLayer(Layer* aLayer)
  {
    mFirstChild = mLastChild = nullptr;
    aLayer->SetParent(nullptr);
  }

  // These getters can be used anytime.
  virtual RefLayer* AsRefLayer() override { return this; }

  virtual int64_t GetReferentId() { return mId; }

  /**
   * DRAWING PHASE ONLY
   */
  virtual void FillSpecificAttributes(SpecificLayerAttributes& aAttrs) override;

  MOZ_LAYER_DECL_NAME("RefLayer", TYPE_REF)

protected:
  RefLayer(LayerManager* aManager, void* aImplData)
    : ContainerLayer(aManager, aImplData) , mId(0)
  {}

  virtual void PrintInfo(std::stringstream& aStream, const char* aPrefix) override;

  virtual void DumpPacket(layerscope::LayersPacket* aPacket, const void* aParent) override;

  // 0 is a special value that means "no ID".
  uint64_t mId;
};

void SetAntialiasingFlags(Layer* aLayer, gfx::DrawTarget* aTarget);

#ifdef MOZ_DUMP_PAINTING
void WriteSnapshotToDumpFile(Layer* aLayer, gfx::DataSourceSurface* aSurf);
void WriteSnapshotToDumpFile(LayerManager* aManager, gfx::DataSourceSurface* aSurf);
void WriteSnapshotToDumpFile(Compositor* aCompositor, gfx::DrawTarget* aTarget);
#endif

// A utility function used by different LayerManager implementations.
gfx::IntRect ToOutsideIntRect(const gfxRect &aRect);

} // namespace layers
} // namespace mozilla

#endif /* GFX_LAYERS_H */