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.

Header

Mercurial (409f3966645a)

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
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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/.
 */

#include "RetainedDisplayListBuilder.h"

#include "DisplayListChecker.h"
#include "gfxPrefs.h"
#include "nsPlaceholderFrame.h"
#include "nsSubDocumentFrame.h"
#include "nsViewManager.h"
#include "nsCanvasFrame.h"

/**
 * Code for doing display list building for a modified subset of the window,
 * and then merging it into the existing display list (for the full window).
 *
 * The approach primarily hinges on the observation that the ‘true’ ordering of
 * display items is represented by a DAG (only items that intersect in 2d space
 * have a defined ordering). Our display list is just one of a many possible
 * linear representations of this ordering.
 *
 * Each time a frame changes (gets a new ComputedStyle, or has a size/position
 * change), we schedule a paint (as we do currently), but also reord the frame
 * that changed.
 *
 * When the next paint occurs we union the overflow areas (in screen space) of
 * the changed frames, and compute a rect/region that contains all changed
 * items. We then build a display list just for this subset of the screen and
 * merge it into the display list from last paint.
 *
 * Any items that exist in one list and not the other must not have a defined
 * ordering in the DAG, since they need to intersect to have an ordering and
 * we would have built both in the new list if they intersected. Given that, we
 * can align items that appear in both lists, and any items that appear between
 * matched items can be inserted into the merged list in any order.
 */

using namespace mozilla;

static void
MarkFramesWithItemsAndImagesModified(nsDisplayList* aList)
{
  for (nsDisplayItem* i = aList->GetBottom(); i != nullptr; i = i->GetAbove()) {
    if (!i->HasDeletedFrame() && i->CanBeReused() &&
        !i->Frame()->IsFrameModified()) {
      // If we have existing cached geometry for this item, then check that for
      // whether we need to invalidate for a sync decode. If we don't, then
      // use the item's flags.
      DisplayItemData* data = FrameLayerBuilder::GetOldDataFor(i);
      // XXX: handle webrender case
      bool invalidate = false;
      if (data && data->GetGeometry()) {
        invalidate = data->GetGeometry()->InvalidateForSyncDecodeImages();
      } else if (!(i->GetFlags() & TYPE_RENDERS_NO_IMAGES)) {
        invalidate = true;
      }

      if (invalidate) {
        i->FrameForInvalidation()->MarkNeedsDisplayItemRebuild();
        if (i->GetDependentFrame()) {
          i->GetDependentFrame()->MarkNeedsDisplayItemRebuild();
        }
      }
    }
    if (i->GetChildren()) {
      MarkFramesWithItemsAndImagesModified(i->GetChildren());
    }
  }
}

static AnimatedGeometryRoot*
SelectAGRForFrame(nsIFrame* aFrame, AnimatedGeometryRoot* aParentAGR)
{
  if (!aFrame->IsStackingContext() || !aFrame->IsFixedPosContainingBlock()) {
    return aParentAGR;
  }

  if (!aFrame->HasOverrideDirtyRegion()) {
    return nullptr;
  }

  nsDisplayListBuilder::DisplayListBuildingData* data =
    aFrame->GetProperty(nsDisplayListBuilder::DisplayListBuildingRect());

  return data && data->mModifiedAGR ? data->mModifiedAGR.get() : nullptr;
}

// Removes any display items that belonged to a frame that was deleted,
// and mark frames that belong to a different AGR so that get their
// items built again.
// TODO: We currently descend into all children even if we don't have an AGR
// to mark, as child stacking contexts might. It would be nice if we could
// jump into those immediately rather than walking the entire thing.
bool
RetainedDisplayListBuilder::PreProcessDisplayList(RetainedDisplayList* aList,
                                                  AnimatedGeometryRoot* aAGR,
                                                  uint32_t aCallerKey,
                                                  uint32_t aNestingDepth)
{
  // The DAG merging algorithm does not have strong mechanisms in place to keep
  // the complexity of the resulting DAG under control. In some cases we can
  // build up edges very quickly. Detect those cases and force a full display
  // list build if we hit them.
  static const uint32_t kMaxEdgeRatio = 5;
  bool initializeDAG = !aList->mDAG.Length();
  if (!initializeDAG && aList->mDAG.mDirectPredecessorList.Length() >
                          (aList->mDAG.mNodesInfo.Length() * kMaxEdgeRatio)) {
    return false;
  }

  MOZ_RELEASE_ASSERT(initializeDAG || aList->mDAG.Length() == aList->Count());

  nsDisplayList saved;
  aList->mOldItems.SetCapacity(aList->Count());
  MOZ_RELEASE_ASSERT(aList->mOldItems.IsEmpty());
  while (nsDisplayItem* item = aList->RemoveBottom()) {
#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
    item->mMergedItem = false;
    item->mPreProcessedItem = true;
#endif

    if (item->HasDeletedFrame() || !item->CanBeReused()) {
      size_t i = aList->mOldItems.Length();
      aList->mOldItems.AppendElement(OldItemInfo(nullptr));
      item->Destroy(&mBuilder);

      if (initializeDAG) {
        if (i == 0) {
          aList->mDAG.AddNode(Span<const MergedListIndex>());
        } else {
          MergedListIndex previous(i - 1);
          aList->mDAG.AddNode(Span<const MergedListIndex>(&previous, 1));
        }
      }
      continue;
    }

    size_t i = aList->mOldItems.Length();
    aList->mOldItems.AppendElement(OldItemInfo(item));
    item->SetOldListIndex(aList, OldListIndex(i), aCallerKey, aNestingDepth);
    if (initializeDAG) {
      if (i == 0) {
        aList->mDAG.AddNode(Span<const MergedListIndex>());
      } else {
        MergedListIndex previous(i - 1);
        aList->mDAG.AddNode(Span<const MergedListIndex>(&previous, 1));
      }
    }

    nsIFrame* f = item->Frame();

    if (item->GetChildren()) {
      if (!PreProcessDisplayList(item->GetChildren(),
                                 SelectAGRForFrame(f, aAGR),
                                 item->GetPerFrameKey(),
                                 aNestingDepth + 1)) {
        return false;
      }
    }

    // TODO: We should be able to check the clipped bounds relative
    // to the common AGR (of both the existing item and the invalidated
    // frame) and determine if they can ever intersect.
    if (aAGR && item->GetAnimatedGeometryRoot()->GetAsyncAGR() != aAGR) {
      mBuilder.MarkFrameForDisplayIfVisible(f, mBuilder.RootReferenceFrame());
    }

    // TODO: This is here because we sometimes reuse the previous display list
    // completely. For optimization, we could only restore the state for reused
    // display items.
    item->RestoreState();
  }
  MOZ_RELEASE_ASSERT(aList->mOldItems.Length() == aList->mDAG.Length());
  aList->RestoreState();
  return true;
}

void
RetainedDisplayListBuilder::IncrementSubDocPresShellPaintCount(
  nsDisplayItem* aItem)
{
  MOZ_ASSERT(aItem->GetType() == DisplayItemType::TYPE_SUBDOCUMENT);

  nsSubDocumentFrame* subDocFrame =
    static_cast<nsDisplaySubDocument*>(aItem)->SubDocumentFrame();
  MOZ_ASSERT(subDocFrame);

  nsIPresShell* presShell = subDocFrame->GetSubdocumentPresShellForPainting(0);
  MOZ_ASSERT(presShell);

  mBuilder.IncrementPresShellPaintCount(presShell);
}

static bool
AnyContentAncestorModified(nsIFrame* aFrame, nsIFrame* aStopAtFrame = nullptr)
{
  for (nsIFrame* f = aFrame; f;
       f = nsLayoutUtils::GetParentOrPlaceholderForCrossDoc(f)) {
    if (f->IsFrameModified()) {
      return true;
    }

    if (aStopAtFrame && f == aStopAtFrame) {
      break;
    }
  }

  return false;
}

static void
UpdateASR(nsDisplayItem* aItem, Maybe<const ActiveScrolledRoot*>& aContainerASR)
{
  if (!aContainerASR) {
    return;
  }

  nsDisplayWrapList* wrapList = aItem->AsDisplayWrapList();
  if (!wrapList) {
    aItem->SetActiveScrolledRoot(aContainerASR.value());
    return;
  }

  wrapList->SetActiveScrolledRoot(ActiveScrolledRoot::PickAncestor(
    wrapList->GetFrameActiveScrolledRoot(), aContainerASR.value()));
}

void
OldItemInfo::AddedMatchToMergedList(RetainedDisplayListBuilder* aBuilder,
                                    MergedListIndex aIndex)
{
  AddedToMergedList(aIndex);
}

void
OldItemInfo::Discard(RetainedDisplayListBuilder* aBuilder,
                     nsTArray<MergedListIndex>&& aDirectPredecessors)
{
  MOZ_ASSERT(!IsUsed());
  mUsed = mDiscarded = true;
  mDirectPredecessors = std::move(aDirectPredecessors);
  if (mItem) {
    mItem->Destroy(aBuilder->Builder());
  }
  mItem = nullptr;
}

bool
OldItemInfo::IsChanged()
{
  return !mItem || mItem->HasDeletedFrame() || !mItem->CanBeReused();
}

/**
 * A C++ implementation of Markus Stange's merge-dags algorithm.
 * https://github.com/mstange/merge-dags
 *
 * MergeState handles combining a new list of display items into an existing
 * DAG and computes the new DAG in a single pass.
 * Each time we add a new item, we resolve all dependencies for it, so that the
 * resulting list and DAG are built in topological ordering.
 */
class MergeState
{
public:
  MergeState(RetainedDisplayListBuilder* aBuilder,
             RetainedDisplayList& aOldList,
             uint32_t aOuterKey)
    : mBuilder(aBuilder)
    , mOldList(&aOldList)
    , mOldItems(std::move(aOldList.mOldItems))
    , mOldDAG(std::move(
        *reinterpret_cast<DirectedAcyclicGraph<OldListUnits>*>(&aOldList.mDAG)))
    , mOuterKey(aOuterKey)
    , mResultIsModified(false)
  {
    mMergedDAG.EnsureCapacityFor(mOldDAG);
    MOZ_RELEASE_ASSERT(mOldItems.Length() == mOldDAG.Length());
  }

  MergedListIndex ProcessItemFromNewList(
    nsDisplayItem* aNewItem,
    const Maybe<MergedListIndex>& aPreviousItem)
  {
    OldListIndex oldIndex;
    if (!HasModifiedFrame(aNewItem) &&
        HasMatchingItemInOldList(aNewItem, &oldIndex)) {
      nsDisplayItem* oldItem = mOldItems[oldIndex.val].mItem;
      MOZ_DIAGNOSTIC_ASSERT(oldItem->GetPerFrameKey() ==
                              aNewItem->GetPerFrameKey() &&
                            oldItem->Frame() == aNewItem->Frame());
      if (!mOldItems[oldIndex.val].IsChanged()) {
        MOZ_DIAGNOSTIC_ASSERT(!mOldItems[oldIndex.val].IsUsed());
        nsDisplayItem* destItem;
        if (ShouldUseNewItem(aNewItem)) {
          destItem = aNewItem;
        } else {
          destItem = oldItem;
          // The building rect can depend on the overflow rect (when the parent
          // frame is position:fixed), which can change without invalidating
          // the frame/items. If we're using the old item, copy the building
          // rect across from the new item.
          oldItem->SetBuildingRect(aNewItem->GetBuildingRect());
        }

        if (aNewItem->GetChildren()) {
          Maybe<const ActiveScrolledRoot*> containerASRForChildren;
          if (mBuilder->MergeDisplayLists(aNewItem->GetChildren(),
                                          oldItem->GetChildren(),
                                          destItem->GetChildren(),
                                          containerASRForChildren,
                                          aNewItem->GetPerFrameKey())) {
            destItem->InvalidateCachedChildInfo();
            mResultIsModified = true;
          }
          UpdateASR(destItem, containerASRForChildren);
          destItem->UpdateBounds(mBuilder->Builder());
        }

        AutoTArray<MergedListIndex, 2> directPredecessors =
          ProcessPredecessorsOfOldNode(oldIndex);
        MergedListIndex newIndex = AddNewNode(
          destItem, Some(oldIndex), directPredecessors, aPreviousItem);
        mOldItems[oldIndex.val].AddedMatchToMergedList(mBuilder, newIndex);
        if (destItem == aNewItem) {
          oldItem->Destroy(mBuilder->Builder());
        } else {
          aNewItem->Destroy(mBuilder->Builder());
        }
        return newIndex;
      }
    }
    mResultIsModified = true;
    return AddNewNode(
      aNewItem, Nothing(), Span<MergedListIndex>(), aPreviousItem);
  }

  bool ShouldUseNewItem(nsDisplayItem* aNewItem)
  {
    // Generally we want to use the old item when the frame isn't marked as
    // modified so that any cached information on the item (or referencing the
    // item) gets retained. Quite a few FrameLayerBuilder performance
    // improvements benefit by this. Sometimes, however, we can end up where the
    // new item paints something different from the old item, even though we
    // haven't modified the frame, and it's hard to fix. In these cases we just
    // always use the new item to be safe.
    DisplayItemType type = aNewItem->GetType();
    if (type == DisplayItemType::TYPE_CANVAS_BACKGROUND_COLOR ||
        type == DisplayItemType::TYPE_SOLID_COLOR) {
      // The canvas background color item can paint the color from another
      // frame, and even though we schedule a paint, we don't mark the canvas
      // frame as invalid.
      return true;
    }

    if (type == DisplayItemType::TYPE_TABLE_BORDER_COLLAPSE) {
      // We intentionally don't mark the root table frame as modified when a
      // subframe changes, even though the border collapse item for the root
      // frame is what paints the changed border. Marking the root frame as
      // modified would rebuild display items for the whole table area, and we
      // don't want that.
      return true;
    }

    if (type == DisplayItemType::TYPE_TEXT_OVERFLOW) {
      // Text overflow marker items are created with the wrapping block as their
      // frame, and have an index value to note which line they are created for.
      // Their rendering can change if the items on that line change, which may
      // not mark the block as modified. We rebuild them if we build any item on
      // the line, so we should always get new items if they might have changed
      // rendering, and it's easier to just use the new items rather than
      // computing if we actually need them.
      return true;
    }

    if (type == DisplayItemType::TYPE_SUBDOCUMENT) {
      // nsDisplaySubDocument::mShouldFlatten can change without an invalidation
      // (and is the reason we unconditionally build the subdocument item), so
      // always use the new one to make sure we get the right value.
      return true;
    }

    if (type == DisplayItemType::TYPE_CARET) {
      // The caret can change position while still being owned by the same frame
      // and we don't invalidate in that case. Use the new version since the
      // changed bounds are needed for DLBI.
      return true;
    }

    return false;
  }

  RetainedDisplayList Finalize()
  {
    for (size_t i = 0; i < mOldDAG.Length(); i++) {
      if (mOldItems[i].IsUsed()) {
        continue;
      }

      AutoTArray<MergedListIndex, 2> directPredecessors =
        ResolveNodeIndexesOldToMerged(
          mOldDAG.GetDirectPredecessors(OldListIndex(i)));
      ProcessOldNode(OldListIndex(i), std::move(directPredecessors));
    }

    RetainedDisplayList result;
    result.AppendToTop(&mMergedItems);
    result.mDAG = std::move(mMergedDAG);
    MOZ_RELEASE_ASSERT(result.mDAG.Length() == result.Count());
    return result;
  }

  bool HasMatchingItemInOldList(nsDisplayItem* aItem, OldListIndex* aOutIndex)
  {
    nsIFrame::DisplayItemArray* items =
      aItem->Frame()->GetProperty(nsIFrame::DisplayItems());
    // Look for an item that matches aItem's frame and per-frame-key, but isn't
    // the same item.
    for (nsDisplayItem* i : *items) {
      if (i != aItem && i->Frame() == aItem->Frame() &&
          i->GetPerFrameKey() == aItem->GetPerFrameKey()) {
        if (i->GetOldListIndex(mOldList, mOuterKey, aOutIndex)) {
          return true;
        }
      }
    }
    return false;
  }

  bool HasModifiedFrame(nsDisplayItem* aItem)
  {
    return AnyContentAncestorModified(aItem->FrameForInvalidation());
  }

  void UpdateContainerASR(nsDisplayItem* aItem)
  {
    const ActiveScrolledRoot* itemClipASR =
      aItem->GetClipChain() ? aItem->GetClipChain()->mASR : nullptr;

    const ActiveScrolledRoot* finiteBoundsASR =
      ActiveScrolledRoot::PickDescendant(itemClipASR,
                                         aItem->GetActiveScrolledRoot());
    if (!mContainerASR) {
      mContainerASR = Some(finiteBoundsASR);
    } else {
      mContainerASR = Some(ActiveScrolledRoot::PickAncestor(
        mContainerASR.value(), finiteBoundsASR));
    }
  }

  MergedListIndex AddNewNode(
    nsDisplayItem* aItem,
    const Maybe<OldListIndex>& aOldIndex,
    Span<const MergedListIndex> aDirectPredecessors,
    const Maybe<MergedListIndex>& aExtraDirectPredecessor)
  {
    UpdateContainerASR(aItem);

#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
    nsIFrame::DisplayItemArray* items =
      aItem->Frame()->GetProperty(nsIFrame::DisplayItems());
    for (nsDisplayItem* i : *items) {
      if (i->Frame() == aItem->Frame() &&
          i->GetPerFrameKey() == aItem->GetPerFrameKey()) {
        MOZ_DIAGNOSTIC_ASSERT(!i->mMergedItem);
      }
    }

    aItem->mMergedItem = true;
    aItem->mPreProcessedItem = false;
#endif

    mMergedItems.AppendToTop(aItem);
    MergedListIndex newIndex =
      mMergedDAG.AddNode(aDirectPredecessors, aExtraDirectPredecessor);
    return newIndex;
  }

  void ProcessOldNode(OldListIndex aNode,
                      nsTArray<MergedListIndex>&& aDirectPredecessors)
  {
    nsDisplayItem* item = mOldItems[aNode.val].mItem;
    if (mOldItems[aNode.val].IsChanged() || HasModifiedFrame(item)) {
      mOldItems[aNode.val].Discard(mBuilder, std::move(aDirectPredecessors));
      mResultIsModified = true;
    } else {
      if (item->GetChildren()) {
        Maybe<const ActiveScrolledRoot*> containerASRForChildren;
        nsDisplayList empty;
        if (mBuilder->MergeDisplayLists(&empty,
                                        item->GetChildren(),
                                        item->GetChildren(),
                                        containerASRForChildren,
                                        item->GetPerFrameKey())) {
          item->InvalidateCachedChildInfo();
          mResultIsModified = true;
        }
        UpdateASR(item, containerASRForChildren);
        item->UpdateBounds(mBuilder->Builder());
      }
      if (item->GetType() == DisplayItemType::TYPE_SUBDOCUMENT) {
        mBuilder->IncrementSubDocPresShellPaintCount(item);
      }
      item->SetReused(true);
      mOldItems[aNode.val].AddedToMergedList(
        AddNewNode(item, Some(aNode), aDirectPredecessors, Nothing()));
    }
  }

  struct PredecessorStackItem
  {
    PredecessorStackItem(OldListIndex aNode, Span<OldListIndex> aPredecessors)
      : mNode(aNode)
      , mDirectPredecessors(aPredecessors)
      , mCurrentPredecessorIndex(0)
    {
    }

    bool IsFinished()
    {
      return mCurrentPredecessorIndex == mDirectPredecessors.Length();
    }

    OldListIndex GetAndIncrementCurrentPredecessor()
    {
      return mDirectPredecessors[mCurrentPredecessorIndex++];
    }

    OldListIndex mNode;
    Span<OldListIndex> mDirectPredecessors;
    size_t mCurrentPredecessorIndex;
  };

  AutoTArray<MergedListIndex, 2> ProcessPredecessorsOfOldNode(
    OldListIndex aNode)
  {
    AutoTArray<PredecessorStackItem, 256> mStack;
    mStack.AppendElement(
      PredecessorStackItem(aNode, mOldDAG.GetDirectPredecessors(aNode)));

    while (true) {
      if (mStack.LastElement().IsFinished()) {
        // If we've finished processing all the entries in the current set, then
        // pop it off the processing stack and process it.
        PredecessorStackItem item = mStack.PopLastElement();
        AutoTArray<MergedListIndex, 2> result =
          ResolveNodeIndexesOldToMerged(item.mDirectPredecessors);

        if (mStack.IsEmpty()) {
          return result;
        }

        ProcessOldNode(item.mNode, std::move(result));
      } else {
        // Grab the current predecessor, push predecessors of that onto the
        // processing stack (if it hasn't already been processed), and then
        // advance to the next entry.
        OldListIndex currentIndex =
          mStack.LastElement().GetAndIncrementCurrentPredecessor();
        if (!mOldItems[currentIndex.val].IsUsed()) {
          mStack.AppendElement(PredecessorStackItem(
            currentIndex, mOldDAG.GetDirectPredecessors(currentIndex)));
        }
      }
    }
  }

  AutoTArray<MergedListIndex, 2> ResolveNodeIndexesOldToMerged(
    Span<OldListIndex> aDirectPredecessors)
  {
    AutoTArray<MergedListIndex, 2> result;
    result.SetCapacity(aDirectPredecessors.Length());
    for (OldListIndex index : aDirectPredecessors) {
      OldItemInfo& oldItem = mOldItems[index.val];
      if (oldItem.IsDiscarded()) {
        for (MergedListIndex inner : oldItem.mDirectPredecessors) {
          if (!result.Contains(inner)) {
            result.AppendElement(inner);
          }
        }
      } else {
        result.AppendElement(oldItem.mIndex);
      }
    }
    return result;
  }

  RetainedDisplayListBuilder* mBuilder;
  RetainedDisplayList* mOldList;
  Maybe<const ActiveScrolledRoot*> mContainerASR;
  nsTArray<OldItemInfo> mOldItems;
  DirectedAcyclicGraph<OldListUnits> mOldDAG;
  // Unfortunately we can't use strong typing for the hashtables
  // since they internally encode the type with the mOps pointer,
  // and assert when we try swap the contents
  nsDisplayList mMergedItems;
  DirectedAcyclicGraph<MergedListUnits> mMergedDAG;
  uint32_t mOuterKey;
  bool mResultIsModified;
};

/**
 * Takes two display lists and merges them into an output list.
 *
 * Display lists wthout an explicit DAG are interpreted as linear DAGs (with a
 * maximum of one direct predecessor and one direct successor per node). We add
 * the two DAGs together, and then output the topological sorted ordering as the
 * final display list.
 *
 * Once we've merged a list, we then retain the DAG (as part of the
 * RetainedDisplayList object) to use for future merges.
 */
bool
RetainedDisplayListBuilder::MergeDisplayLists(
  nsDisplayList* aNewList,
  RetainedDisplayList* aOldList,
  RetainedDisplayList* aOutList,
  mozilla::Maybe<const mozilla::ActiveScrolledRoot*>& aOutContainerASR,
  uint32_t aOuterKey)
{
  MergeState merge(this, *aOldList, aOuterKey);

  Maybe<MergedListIndex> previousItemIndex;
  while (nsDisplayItem* item = aNewList->RemoveBottom()) {
    previousItemIndex =
      Some(merge.ProcessItemFromNewList(item, previousItemIndex));
  }

  *aOutList = merge.Finalize();
  aOutContainerASR = merge.mContainerASR;
  return merge.mResultIsModified;
}

static void
TakeAndAddModifiedAndFramesWithPropsFromRootFrame(
  nsTArray<nsIFrame*>* aModifiedFrames,
  nsTArray<nsIFrame*>* aFramesWithProps,
  nsIFrame* aRootFrame)
{
  MOZ_ASSERT(aRootFrame);

  nsTArray<nsIFrame*>* frames =
    aRootFrame->GetProperty(nsIFrame::ModifiedFrameList());

  if (frames) {
    for (nsIFrame* f : *frames) {
      if (f) {
        aModifiedFrames->AppendElement(f);
      }
    }

    frames->Clear();
  }

  frames = aRootFrame->GetProperty(nsIFrame::OverriddenDirtyRectFrameList());

  if (frames) {
    for (nsIFrame* f : *frames) {
      if (f) {
        aFramesWithProps->AppendElement(f);
      }
    }

    frames->Clear();
  }
}

struct CbData
{
  nsDisplayListBuilder* builder;
  nsTArray<nsIFrame*>* modifiedFrames;
  nsTArray<nsIFrame*>* framesWithProps;
};

static nsIFrame*
GetRootFrameForPainting(nsDisplayListBuilder* aBuilder, nsIDocument* aDocument)
{
  // Although this is the actual subdocument, it might not be
  // what painting uses. Walk up to the nsSubDocumentFrame owning
  // us, and then ask that which subdoc it's going to paint.

  nsIPresShell* presShell = aDocument->GetShell();
  if (!presShell) {
    return nullptr;
  }
  nsView* rootView = presShell->GetViewManager()->GetRootView();
  if (!rootView) {
    return nullptr;
  }

  // There should be an anonymous inner view between the root view
  // of the subdoc, and the view for the nsSubDocumentFrame.
  nsView* innerView = rootView->GetParent();
  if (!innerView) {
    return nullptr;
  }

  nsView* subDocView = innerView->GetParent();
  if (!subDocView) {
    return nullptr;
  }

  nsIFrame* subDocFrame = subDocView->GetFrame();
  if (!subDocFrame) {
    return nullptr;
  }

  nsSubDocumentFrame* subdocumentFrame = do_QueryFrame(subDocFrame);
  MOZ_ASSERT(subdocumentFrame);
  presShell = subdocumentFrame->GetSubdocumentPresShellForPainting(
    aBuilder->IsIgnoringPaintSuppression()
      ? nsSubDocumentFrame::IGNORE_PAINT_SUPPRESSION
      : 0);
  return presShell ? presShell->GetRootFrame() : nullptr;
}

static bool
SubDocEnumCb(nsIDocument* aDocument, void* aData)
{
  MOZ_ASSERT(aDocument);
  MOZ_ASSERT(aData);

  CbData* data = static_cast<CbData*>(aData);

  nsIFrame* rootFrame = GetRootFrameForPainting(data->builder, aDocument);
  if (rootFrame) {
    TakeAndAddModifiedAndFramesWithPropsFromRootFrame(
      data->modifiedFrames, data->framesWithProps, rootFrame);

    nsIDocument* innerDoc = rootFrame->PresShell()->GetDocument();
    if (innerDoc) {
      innerDoc->EnumerateSubDocuments(SubDocEnumCb, aData);
    }
  }
  return true;
}

static void
GetModifiedAndFramesWithProps(nsDisplayListBuilder* aBuilder,
                              nsTArray<nsIFrame*>* aOutModifiedFrames,
                              nsTArray<nsIFrame*>* aOutFramesWithProps)
{
  MOZ_ASSERT(aBuilder->RootReferenceFrame());

  TakeAndAddModifiedAndFramesWithPropsFromRootFrame(
    aOutModifiedFrames, aOutFramesWithProps, aBuilder->RootReferenceFrame());

  nsIDocument* rootdoc =
    aBuilder->RootReferenceFrame()->PresContext()->Document();

  if (rootdoc) {
    CbData data = { aBuilder, aOutModifiedFrames, aOutFramesWithProps };

    rootdoc->EnumerateSubDocuments(SubDocEnumCb, &data);
  }
}

// ComputeRebuildRegion  debugging
// #define CRR_DEBUG 1
#if CRR_DEBUG
#define CRR_LOG(...) printf_stderr(__VA_ARGS__)
#else
#define CRR_LOG(...)
#endif

static nsDisplayItem*
GetFirstDisplayItemWithChildren(nsIFrame* aFrame)
{
  nsIFrame::DisplayItemArray* items =
    aFrame->GetProperty(nsIFrame::DisplayItems());
  if (!items) {
    return nullptr;
  }

  for (nsDisplayItem* i : *items) {
    if (i->GetChildren()) {
      return i;
    }
  }
  return nullptr;
}

static bool
IsInPreserve3DContext(const nsIFrame* aFrame)
{
  return aFrame->Extend3DContext() ||
         aFrame->Combines3DTransformWithAncestors();
}

static bool
ProcessFrameInternal(nsIFrame* aFrame,
                     nsDisplayListBuilder& aBuilder,
                     AnimatedGeometryRoot** aAGR,
                     nsRect& aOverflow,
                     nsIFrame* aStopAtFrame,
                     nsTArray<nsIFrame*>& aOutFramesWithProps,
                     const bool aStopAtStackingContext)
{
  nsIFrame* currentFrame = aFrame;

  while (currentFrame != aStopAtFrame) {
    CRR_LOG("currentFrame: %p (placeholder=%d), aOverflow: %d %d %d %d\n",
            currentFrame,
            !aStopAtStackingContext,
            aOverflow.x,
            aOverflow.y,
            aOverflow.width,
            aOverflow.height);

    // If the current frame is an OOF frame, DisplayListBuildingData needs to be
    // set on all the ancestor stacking contexts of the  placeholder frame, up
    // to the containing block of the OOF frame. This is done to ensure that the
    // content that might be behind the OOF frame is built for merging.
    nsIFrame* placeholder = currentFrame->HasAnyStateBits(NS_FRAME_OUT_OF_FLOW)
                              ? currentFrame->GetPlaceholderFrame()
                              : nullptr;

    if (placeholder) {
      // The rect aOverflow is in the coordinate space of the containing block.
      // Convert it to a coordinate space of the placeholder frame.
      nsRect placeholderOverflow =
        aOverflow + currentFrame->GetOffsetTo(placeholder);

      CRR_LOG("Processing placeholder %p for OOF frame %p\n",
              placeholder,
              currentFrame);

      CRR_LOG("OOF frame draw area: %d %d %d %d\n",
              placeholderOverflow.x,
              placeholderOverflow.y,
              placeholderOverflow.width,
              placeholderOverflow.height);

      // Tracking AGRs for the placeholder processing is not necessary, as the
      // goal is to only modify the DisplayListBuildingData rect.
      AnimatedGeometryRoot* dummyAGR = nullptr;

      // Find a common ancestor frame to handle frame continuations.
      // TODO: It might be possible to write a more specific and efficient
      // function for this.
      nsIFrame* ancestor = nsLayoutUtils::FindNearestCommonAncestorFrame(
        currentFrame->GetParent(), placeholder->GetParent());

      if (!ProcessFrameInternal(placeholder,
                                aBuilder,
                                &dummyAGR,
                                placeholderOverflow,
                                ancestor,
                                aOutFramesWithProps,
                                false)) {
        return false;
      }
    }

    // Convert 'aOverflow' into the coordinate space of the nearest stacking
    // context or display port ancestor and update 'currentFrame' to point to
    // that frame.
    aOverflow = nsLayoutUtils::TransformFrameRectToAncestor(
      currentFrame,
      aOverflow,
      aStopAtFrame,
      nullptr,
      nullptr,
      /* aStopAtStackingContextAndDisplayPortAndOOFFrame = */ true,
      &currentFrame);
    if (IsInPreserve3DContext(currentFrame)) {
      return false;
    }

    MOZ_ASSERT(currentFrame);

    if (nsLayoutUtils::FrameHasDisplayPort(currentFrame)) {
      CRR_LOG("Frame belongs to displayport frame %p\n", currentFrame);
      nsIScrollableFrame* sf = do_QueryFrame(currentFrame);
      MOZ_ASSERT(sf);
      nsRect displayPort;
      DebugOnly<bool> hasDisplayPort = nsLayoutUtils::GetDisplayPort(
        currentFrame->GetContent(), &displayPort, RelativeTo::ScrollPort);
      MOZ_ASSERT(hasDisplayPort);
      // get it relative to the scrollport (from the scrollframe)
      nsRect r = aOverflow - sf->GetScrollPortRect().TopLeft();
      r.IntersectRect(r, displayPort);
      if (!r.IsEmpty()) {
        nsRect* rect = currentFrame->GetProperty(
          nsDisplayListBuilder::DisplayListBuildingDisplayPortRect());
        if (!rect) {
          rect = new nsRect();
          currentFrame->SetProperty(
            nsDisplayListBuilder::DisplayListBuildingDisplayPortRect(), rect);
          currentFrame->SetHasOverrideDirtyRegion(true);
          aOutFramesWithProps.AppendElement(currentFrame);
        }
        rect->UnionRect(*rect, r);
        CRR_LOG("Adding area to displayport draw area: %d %d %d %d\n",
                r.x,
                r.y,
                r.width,
                r.height);

        // TODO: Can we just use MarkFrameForDisplayIfVisible, plus
        // MarkFramesForDifferentAGR to ensure that this displayport, plus any
        // items that move relative to it get rebuilt, and then not contribute
        // to the root dirty area?
        aOverflow = sf->GetScrollPortRect();
      } else {
        // Don't contribute to the root dirty area at all.
        aOverflow.SetEmpty();
      }
    } else {
      aOverflow.IntersectRect(
        aOverflow, currentFrame->GetVisualOverflowRectRelativeToSelf());
    }

    if (aOverflow.IsEmpty()) {
      break;
    }

    if (currentFrame != aBuilder.RootReferenceFrame() &&
        currentFrame->IsStackingContext() &&
        currentFrame->IsFixedPosContainingBlock()) {
      CRR_LOG("Frame belongs to stacking context frame %p\n", currentFrame);
      // If we found an intermediate stacking context with an existing display
      // item then we can store the dirty rect there and stop. If we couldn't
      // find one then we need to keep bubbling up to the next stacking context.
      nsDisplayItem* wrapperItem =
        GetFirstDisplayItemWithChildren(currentFrame);
      if (!wrapperItem) {
        continue;
      }

      // Store the stacking context relative dirty area such
      // that display list building will pick it up when it
      // gets to it.
      nsDisplayListBuilder::DisplayListBuildingData* data =
        currentFrame->GetProperty(
          nsDisplayListBuilder::DisplayListBuildingRect());
      if (!data) {
        data = new nsDisplayListBuilder::DisplayListBuildingData();
        currentFrame->SetProperty(
          nsDisplayListBuilder::DisplayListBuildingRect(), data);
        currentFrame->SetHasOverrideDirtyRegion(true);
        aOutFramesWithProps.AppendElement(currentFrame);
      }
      CRR_LOG("Adding area to stacking context draw area: %d %d %d %d\n",
              aOverflow.x,
              aOverflow.y,
              aOverflow.width,
              aOverflow.height);
      data->mDirtyRect.UnionRect(data->mDirtyRect, aOverflow);

      if (!aStopAtStackingContext) {
        // Continue ascending the frame tree until we reach aStopAtFrame.
        continue;
      }

      // Grab the visible (display list building) rect for children of this
      // wrapper item and convert into into coordinate relative to the current
      // frame.
      nsRect previousVisible = wrapperItem->GetBuildingRectForChildren();
      if (wrapperItem->ReferenceFrameForChildren() ==
          wrapperItem->ReferenceFrame()) {
        previousVisible -= wrapperItem->ToReferenceFrame();
      } else {
        MOZ_ASSERT(wrapperItem->ReferenceFrameForChildren() ==
                   wrapperItem->Frame());
      }

      if (!previousVisible.Contains(aOverflow)) {
        // If the overflow area of the changed frame isn't contained within the
        // old item, then we might change the size of the item and need to
        // update its sorting accordingly. Keep propagating the overflow area up
        // so that we build intersecting items for sorting.
        continue;
      }

      if (!data->mModifiedAGR) {
        data->mModifiedAGR = *aAGR;
      } else if (data->mModifiedAGR != *aAGR) {
        data->mDirtyRect = currentFrame->GetVisualOverflowRectRelativeToSelf();
        CRR_LOG("Found multiple modified AGRs within this stacking context, "
                "giving up\n");
      }

      // Don't contribute to the root dirty area at all.
      aOverflow.SetEmpty();
      *aAGR = nullptr;

      break;
    }
  }
  return true;
}

bool
RetainedDisplayListBuilder::ProcessFrame(
  nsIFrame* aFrame,
  nsDisplayListBuilder& aBuilder,
  nsIFrame* aStopAtFrame,
  nsTArray<nsIFrame*>& aOutFramesWithProps,
  const bool aStopAtStackingContext,
  nsRect* aOutDirty,
  AnimatedGeometryRoot** aOutModifiedAGR)
{
  if (aFrame->HasOverrideDirtyRegion()) {
    aOutFramesWithProps.AppendElement(aFrame);
  }

  if (aFrame->HasAnyStateBits(NS_FRAME_IN_POPUP)) {
    return true;
  }

  // TODO: There is almost certainly a faster way of doing this, probably can be
  // combined with the ancestor walk for TransformFrameRectToAncestor.
  AnimatedGeometryRoot* agr =
    aBuilder.FindAnimatedGeometryRootFor(aFrame)->GetAsyncAGR();

  CRR_LOG("Processing frame %p with agr %p\n", aFrame, agr->mFrame);

  // Convert the frame's overflow rect into the coordinate space
  // of the nearest stacking context that has an existing display item.
  // We store that as a dirty rect on that stacking context so that we build
  // all items that intersect the changed frame within the stacking context,
  // and then we use MarkFrameForDisplayIfVisible to make sure the stacking
  // context itself gets built. We don't need to build items that intersect
  // outside of the stacking context, since we know the stacking context item
  // exists in the old list, so we can trivially merge without needing other
  // items.
  nsRect overflow = aFrame->GetVisualOverflowRectRelativeToSelf();

  // If the modified frame is also a caret frame, include the caret area.
  // This is needed because some frames (for example text frames without text)
  // might have an empty overflow rect.
  if (aFrame == aBuilder.GetCaretFrame()) {
    overflow.UnionRect(overflow, aBuilder.GetCaretRect());
  }

  if (!ProcessFrameInternal(aFrame,
                            aBuilder,
                            &agr,
                            overflow,
                            aStopAtFrame,
                            aOutFramesWithProps,
                            aStopAtStackingContext)) {
    return false;
  }

  if (!overflow.IsEmpty()) {
    aOutDirty->UnionRect(*aOutDirty, overflow);
    CRR_LOG("Adding area to root draw area: %d %d %d %d\n",
            overflow.x,
            overflow.y,
            overflow.width,
            overflow.height);

    // If we get changed frames from multiple AGRS, then just give up as it gets
    // really complex to track which items would need to be marked in
    // MarkFramesForDifferentAGR.
    if (!*aOutModifiedAGR) {
      CRR_LOG("Setting %p as root stacking context AGR\n", agr);
      *aOutModifiedAGR = agr;
    } else if (agr && *aOutModifiedAGR != agr) {
      CRR_LOG("Found multiple AGRs in root stacking context, giving up\n");
      return false;
    }
  }
  return true;
}

static void
AddFramesForContainingBlock(nsIFrame* aBlock,
                            const nsFrameList& aFrames,
                            nsTArray<nsIFrame*>& aExtraFrames)
{
  for (nsIFrame* f : aFrames) {
    if (!f->IsFrameModified() && AnyContentAncestorModified(f, aBlock)) {
      CRR_LOG("Adding invalid OOF %p\n", f);
      aExtraFrames.AppendElement(f);
    }
  }
}

// Placeholder descendants of aFrame don't contribute to aFrame's overflow area.
// Find all the containing blocks that might own placeholders under us, walk
// their OOF frames list, and manually invalidate any frames that are
// descendants of a modified frame (us, or another frame we'll get to soon).
// This is combined with the work required for MarkFrameForDisplayIfVisible,
// so that we can avoid an extra ancestor walk, and we can reuse the flag
// to detect when we've already visited an ancestor (and thus all further
// ancestors must also be visited).
void
FindContainingBlocks(nsIFrame* aFrame, nsTArray<nsIFrame*>& aExtraFrames)
{
  for (nsIFrame* f = aFrame; f;
       f = nsLayoutUtils::GetParentOrPlaceholderForCrossDoc(f)) {
    if (f->ForceDescendIntoIfVisible())
      return;
    f->SetForceDescendIntoIfVisible(true);
    CRR_LOG("Considering OOFs for %p\n", f);

    AddFramesForContainingBlock(
      f, f->GetChildList(nsIFrame::kFloatList), aExtraFrames);
    AddFramesForContainingBlock(
      f, f->GetChildList(f->GetAbsoluteListID()), aExtraFrames);
  }
}

/**
 * Given a list of frames that has been modified, computes the region that we
 * need to do display list building for in order to build all modified display
 * items.
 *
 * When a modified frame is within a stacking context (with an existing display
 * item), then we only contribute to the build area within the stacking context,
 * as well as forcing display list building to descend to the stacking context.
 * We don't need to add build area outside of the stacking context (and force
 * items above/below the stacking context container item to be built), since
 * just matching the position of the stacking context container item is
 * sufficient to ensure correct ordering during merging.
 *
 * We need to rebuild all items that might intersect with the modified frame,
 * both now and during async changes on the compositor. We do this by rebuilding
 * the area covered by the changed frame, as well as rebuilding all items that
 * have a different (async) AGR to the changed frame. If we have changes to
 * multiple AGRs (within a stacking context), then we rebuild that stacking
 * context entirely.
 *
 * @param aModifiedFrames The list of modified frames.
 * @param aOutDirty The result region to use for display list building.
 * @param aOutModifiedAGR The modified AGR for the root stacking context.
 * @param aOutFramesWithProps The list of frames to which we attached partial
 * build data so that it can be cleaned up.
 *
 * @return true if we succesfully computed a partial rebuild region, false if a
 * full build is required.
 */
bool
RetainedDisplayListBuilder::ComputeRebuildRegion(
  nsTArray<nsIFrame*>& aModifiedFrames,
  nsRect* aOutDirty,
  AnimatedGeometryRoot** aOutModifiedAGR,
  nsTArray<nsIFrame*>& aOutFramesWithProps)
{
  CRR_LOG("Computing rebuild regions for %zu frames:\n",
          aModifiedFrames.Length());
  nsTArray<nsIFrame*> extraFrames;
  for (nsIFrame* f : aModifiedFrames) {
    MOZ_ASSERT(f);

    mBuilder.AddFrameMarkedForDisplayIfVisible(f);
    FindContainingBlocks(f, extraFrames);

    if (!ProcessFrame(f,
                      mBuilder,
                      mBuilder.RootReferenceFrame(),
                      aOutFramesWithProps,
                      true,
                      aOutDirty,
                      aOutModifiedAGR)) {
      return false;
    }
  }

  for (nsIFrame* f : extraFrames) {
    mBuilder.MarkFrameModifiedDuringBuilding(f);

    if (!ProcessFrame(f,
                      mBuilder,
                      mBuilder.RootReferenceFrame(),
                      aOutFramesWithProps,
                      true,
                      aOutDirty,
                      aOutModifiedAGR)) {
      return false;
    }
  }

  return true;
}

/*
 * A simple early exit heuristic to avoid slow partial display list rebuilds.
 */
static bool
ShouldBuildPartial(nsTArray<nsIFrame*>& aModifiedFrames)
{
  if (aModifiedFrames.Length() > gfxPrefs::LayoutRebuildFrameLimit()) {
    return false;
  }

  for (nsIFrame* f : aModifiedFrames) {
    MOZ_ASSERT(f);

    const LayoutFrameType type = f->Type();

    // If we have any modified frames of the following types, it is likely that
    // doing a partial rebuild of the display list will be slower than doing a
    // full rebuild.
    // This is because these frames either intersect or may intersect with most
    // of the page content. This is either due to display port size or different
    // async AGR.
    if (type == LayoutFrameType::Viewport ||
        type == LayoutFrameType::PageContent ||
        type == LayoutFrameType::Canvas || type == LayoutFrameType::Scrollbar) {
      return false;
    }
  }

  return true;
}

static void
ClearFrameProps(nsTArray<nsIFrame*>& aFrames)
{
  for (nsIFrame* f : aFrames) {
    if (f->HasOverrideDirtyRegion()) {
      f->SetHasOverrideDirtyRegion(false);
      f->DeleteProperty(nsDisplayListBuilder::DisplayListBuildingRect());
      f->DeleteProperty(
        nsDisplayListBuilder::DisplayListBuildingDisplayPortRect());
    }

    f->SetFrameIsModified(false);
  }
}

class AutoClearFramePropsArray
{
public:
  AutoClearFramePropsArray() = default;

  ~AutoClearFramePropsArray() { ClearFrameProps(mFrames); }

  nsTArray<nsIFrame*>& Frames() { return mFrames; }

  bool IsEmpty() const { return mFrames.IsEmpty(); }

private:
  nsTArray<nsIFrame*> mFrames;
};

void
RetainedDisplayListBuilder::ClearFramesWithProps()
{
  AutoClearFramePropsArray modifiedFrames;
  AutoClearFramePropsArray framesWithProps;
  GetModifiedAndFramesWithProps(
    &mBuilder, &modifiedFrames.Frames(), &framesWithProps.Frames());
}

auto
RetainedDisplayListBuilder::AttemptPartialUpdate(
  nscolor aBackstop,
  mozilla::DisplayListChecker* aChecker) -> PartialUpdateResult
{
  mBuilder.RemoveModifiedWindowRegions();
  mBuilder.ClearWindowOpaqueRegion();

  if (mBuilder.ShouldSyncDecodeImages()) {
    MarkFramesWithItemsAndImagesModified(&mList);
  }

  mBuilder.EnterPresShell(mBuilder.RootReferenceFrame());

  // We set the override dirty regions during ComputeRebuildRegion or in
  // nsLayoutUtils::InvalidateForDisplayPortChange. The display port change also
  // marks the frame modified, so those regions are cleared here as well.
  AutoClearFramePropsArray modifiedFrames;
  AutoClearFramePropsArray framesWithProps;
  GetModifiedAndFramesWithProps(
    &mBuilder, &modifiedFrames.Frames(), &framesWithProps.Frames());

  // Do not allow partial builds if the retained display list is empty, or if
  // ShouldBuildPartial heuristic fails.
  bool shouldBuildPartial =
    !mList.IsEmpty() && ShouldBuildPartial(modifiedFrames.Frames());

  // We don't support retaining with overlay scrollbars, since they require
  // us to look at the display list and pick the highest z-index, which
  // we can't do during partial building.
  if (mBuilder.DisablePartialUpdates()) {
    shouldBuildPartial = false;
    mBuilder.SetDisablePartialUpdates(false);
  }

  if (mPreviousCaret != mBuilder.GetCaretFrame()) {
    if (mPreviousCaret) {
      if (mBuilder.MarkFrameModifiedDuringBuilding(mPreviousCaret)) {
        modifiedFrames.Frames().AppendElement(mPreviousCaret);
      }
    }

    if (mBuilder.GetCaretFrame()) {
      if (mBuilder.MarkFrameModifiedDuringBuilding(mBuilder.GetCaretFrame())) {
        modifiedFrames.Frames().AppendElement(mBuilder.GetCaretFrame());
      }
    }

    mPreviousCaret = mBuilder.GetCaretFrame();
  }

  nsRect modifiedDirty;
  AnimatedGeometryRoot* modifiedAGR = nullptr;
  if (!shouldBuildPartial ||
      !ComputeRebuildRegion(modifiedFrames.Frames(),
                            &modifiedDirty,
                            &modifiedAGR,
                            framesWithProps.Frames()) ||
      !PreProcessDisplayList(&mList, modifiedAGR)) {
    mBuilder.LeavePresShell(mBuilder.RootReferenceFrame(), List());
    mList.DeleteAll(&mBuilder);
    return PartialUpdateResult::Failed;
  }

  // This is normally handled by EnterPresShell, but we skipped it so that we
  // didn't call MarkFrameForDisplayIfVisible before ComputeRebuildRegion.
  nsIScrollableFrame* sf = mBuilder.RootReferenceFrame()
                             ->PresShell()
                             ->GetRootScrollFrameAsScrollable();
  if (sf) {
    nsCanvasFrame* canvasFrame = do_QueryFrame(sf->GetScrolledFrame());
    if (canvasFrame) {
      mBuilder.MarkFrameForDisplayIfVisible(canvasFrame,
                                            mBuilder.RootReferenceFrame());
    }
  }

  modifiedDirty.IntersectRect(
    modifiedDirty,
    mBuilder.RootReferenceFrame()->GetVisualOverflowRectRelativeToSelf());

  PartialUpdateResult result = PartialUpdateResult::NoChange;
  if (!modifiedDirty.IsEmpty() || !framesWithProps.IsEmpty()) {
    result = PartialUpdateResult::Updated;
  }

  mBuilder.SetDirtyRect(modifiedDirty);
  mBuilder.SetPartialUpdate(true);

  nsDisplayList modifiedDL;
  mBuilder.RootReferenceFrame()->BuildDisplayListForStackingContext(
    &mBuilder, &modifiedDL);
  if (!modifiedDL.IsEmpty()) {
    nsLayoutUtils::AddExtraBackgroundItems(
      mBuilder,
      modifiedDL,
      mBuilder.RootReferenceFrame(),
      nsRect(nsPoint(0, 0), mBuilder.RootReferenceFrame()->GetSize()),
      mBuilder.RootReferenceFrame()->GetVisualOverflowRectRelativeToSelf(),
      aBackstop);
  }
  mBuilder.SetPartialUpdate(false);

  if (mBuilder.PartialBuildFailed()) {
    mBuilder.SetPartialBuildFailed(false);
    mBuilder.LeavePresShell(mBuilder.RootReferenceFrame(), List());
    mList.DeleteAll(&mBuilder);
    modifiedDL.DeleteAll(&mBuilder);
    return PartialUpdateResult::Failed;
  }

  if (aChecker) {
    aChecker->Set(&modifiedDL, "TM");
  }

  // printf_stderr("Painting --- Modified list (dirty %d,%d,%d,%d):\n",
  //              modifiedDirty.x, modifiedDirty.y, modifiedDirty.width,
  //              modifiedDirty.height);
  // nsFrame::PrintDisplayList(&mBuilder, modifiedDL);

  // |modifiedDL| can sometimes be empty here. We still perform the
  // display list merging to prune unused items (for example, items that
  // are not visible anymore) from the old list.
  // TODO: Optimization opportunity. In this case, MergeDisplayLists()
  // unnecessarily creates a hashtable of the old items.
  // TODO: Ideally we could skip this if result is NoChange, but currently when
  // we call RestoreState on nsDisplayWrapList it resets the clip to the base
  // clip, and we need the UpdateBounds call (within MergeDisplayLists) to
  // move it to the correct inner clip.
  Maybe<const ActiveScrolledRoot*> dummy;
  if (MergeDisplayLists(&modifiedDL, &mList, &mList, dummy)) {
    result = PartialUpdateResult::Updated;
  }

  // printf_stderr("Painting --- Merged list:\n");
  // nsFrame::PrintDisplayList(&mBuilder, mList);

  mBuilder.LeavePresShell(mBuilder.RootReferenceFrame(), List());
  return result;
}