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 (56e7b9127e89)

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
/* -*- 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 "LayerTreeInvalidation.h"

#include <stdint.h>                     // for uint32_t
#include "ImageContainer.h"             // for ImageContainer
#include "ImageLayers.h"                // for ImageLayer, etc
#include "Layers.h"                     // for Layer, ContainerLayer, etc
#include "Units.h"                      // for ParentLayerIntRect
#include "gfxRect.h"                    // for gfxRect
#include "gfxUtils.h"                   // for gfxUtils
#include "mozilla/ArrayUtils.h"         // for ArrayEqual
#include "mozilla/gfx/BaseSize.h"       // for BaseSize
#include "mozilla/gfx/Point.h"          // for IntSize
#include "mozilla/mozalloc.h"           // for operator new, etc
#include "nsDataHashtable.h"            // for nsDataHashtable
#include "nsDebug.h"                    // for NS_ASSERTION
#include "nsHashKeys.h"                 // for nsPtrHashKey
#include "nsISupportsImpl.h"            // for Layer::AddRef, etc
#include "nsRect.h"                     // for IntRect
#include "nsTArray.h"                   // for AutoTArray, nsTArray_Impl
#include "mozilla/Poison.h"
#include "mozilla/layers/ImageHost.h"
#include "mozilla/layers/LayerManagerComposite.h"
#include "TreeTraversal.h"              // for ForEachNode
#include "LayersLogging.h"

// LayerTreeInvalidation debugging
#define LTI_DEBUG 0

#if LTI_DEBUG
#  define LTI_DEEPER(aPrefix) nsPrintfCString("%s  ", aPrefix).get()
#  define LTI_DUMP(rgn, label) if (!(rgn).IsEmpty()) printf_stderr("%s%p: " label " portion is %s\n", aPrefix, mLayer.get(), Stringify(rgn).c_str());
#  define LTI_LOG(...) printf_stderr(__VA_ARGS__)
#else
#  define LTI_DEEPER(aPrefix) nullptr
#  define LTI_DUMP(rgn, label)
#  define LTI_LOG(...)
#endif

using namespace mozilla::gfx;

namespace mozilla {
namespace layers {

struct LayerPropertiesBase;
UniquePtr<LayerPropertiesBase> CloneLayerTreePropertiesInternal(Layer* aRoot, bool aIsMask = false);

/**
 * Get accumulated transform of from the context creating layer to the
 * given layer.
 */
static Matrix4x4
GetTransformIn3DContext(Layer* aLayer) {
  Matrix4x4 transform = aLayer->GetLocalTransform();
  for (Layer* layer = aLayer->GetParent();
       layer && layer->Extend3DContext();
       layer = layer->GetParent()) {
    transform = transform * layer->GetLocalTransform();
  }
  return transform;
}

/**
 * Get a transform for the given layer depending on extending 3D
 * context.
 *
 * @return local transform for layers not participating 3D rendering
 * context, or the accmulated transform in the context for else.
 */
static Matrix4x4Flagged
GetTransformForInvalidation(Layer* aLayer) {
  return (!aLayer->Is3DContextLeaf() && !aLayer->Extend3DContext() ?
          aLayer->GetLocalTransform() : GetTransformIn3DContext(aLayer));
}

static IntRect
TransformRect(const IntRect& aRect, const Matrix4x4Flagged& aTransform)
{
  if (aRect.IsEmpty()) {
    return IntRect();
  }

  Rect rect(aRect.X(), aRect.Y(), aRect.Width(), aRect.Height());
  rect = aTransform.TransformAndClipBounds(rect, Rect::MaxIntRect());
  rect.RoundOut();

  IntRect intRect;
  if (!gfxUtils::GfxRectToIntRect(ThebesRect(rect), &intRect)) {
    return IntRect();
  }

  return intRect;
}

static void
AddTransformedRegion(nsIntRegion& aDest, const nsIntRegion& aSource, const Matrix4x4Flagged& aTransform)
{
  for (auto iter = aSource.RectIter(); !iter.Done(); iter.Next()) {
    aDest.Or(aDest, TransformRect(iter.Get(), aTransform));
  }
  aDest.SimplifyOutward(20);
}

static void
AddRegion(nsIntRegion& aDest, const nsIntRegion& aSource)
{
  aDest.Or(aDest, aSource);
  aDest.SimplifyOutward(20);
}

/**
 * Walks over this layer, and all descendant layers.
 * If any of these are a ContainerLayer that reports invalidations to a PresShell,
 * then report that the entire bounds have changed.
 */
static void
NotifySubdocumentInvalidation(Layer* aLayer, NotifySubDocInvalidationFunc aCallback)
{
  ForEachNode<ForwardIterator>(
      aLayer,
      [aCallback] (Layer* layer)
      {
        layer->ClearInvalidRegion();
        if (layer->GetMaskLayer()) {
          NotifySubdocumentInvalidation(layer->GetMaskLayer(), aCallback);
        }
        for (size_t i = 0; i < layer->GetAncestorMaskLayerCount(); i++) {
          Layer* maskLayer = layer->GetAncestorMaskLayerAt(i);
          NotifySubdocumentInvalidation(maskLayer, aCallback);
        }
      },
      [aCallback] (Layer* layer)
      {
        ContainerLayer* container = layer->AsContainerLayer();
        if (container) {
          nsIntRegion region = container->GetLocalVisibleRegion().ToUnknownRegion();
          aCallback(container, &region);
        }
      });
}

struct LayerPropertiesBase : public LayerProperties
{
  explicit LayerPropertiesBase(Layer* aLayer)
    : mLayer(aLayer)
    , mMaskLayer(nullptr)
    , mVisibleRegion(mLayer->GetLocalVisibleRegion().ToUnknownRegion())
    , mPostXScale(aLayer->GetPostXScale())
    , mPostYScale(aLayer->GetPostYScale())
    , mOpacity(aLayer->GetLocalOpacity())
    , mUseClipRect(!!aLayer->GetLocalClipRect())
  {
    MOZ_COUNT_CTOR(LayerPropertiesBase);
    if (aLayer->GetMaskLayer()) {
      mMaskLayer = CloneLayerTreePropertiesInternal(aLayer->GetMaskLayer(), true);
    }
    for (size_t i = 0; i < aLayer->GetAncestorMaskLayerCount(); i++) {
      Layer* maskLayer = aLayer->GetAncestorMaskLayerAt(i);
      mAncestorMaskLayers.AppendElement(CloneLayerTreePropertiesInternal(maskLayer, true));
    }
    if (mUseClipRect) {
      mClipRect = *aLayer->GetLocalClipRect();
    }
    mTransform = GetTransformForInvalidation(aLayer);
  }
  LayerPropertiesBase()
    : mLayer(nullptr)
    , mMaskLayer(nullptr)
    , mPostXScale(0.0)
    , mPostYScale(0.0)
    , mOpacity(0.0)
    , mUseClipRect(false)
  {
    MOZ_COUNT_CTOR(LayerPropertiesBase);
  }
  ~LayerPropertiesBase() override
  {
    MOZ_COUNT_DTOR(LayerPropertiesBase);
  }

protected:
  LayerPropertiesBase(const LayerPropertiesBase& a) = delete;
  LayerPropertiesBase& operator=(const LayerPropertiesBase& a) = delete;

public:
  bool ComputeDifferences(Layer* aRoot,
                          nsIntRegion& aOutRegion,
                          NotifySubDocInvalidationFunc aCallback) override;

  void MoveBy(const IntPoint& aOffset) override;

  bool ComputeChange(const char* aPrefix,
                     nsIntRegion& aOutRegion,
                     NotifySubDocInvalidationFunc aCallback)
  {
    // Bug 1251615: This canary is sometimes hit. We're still not sure why.
    mCanary.Check();
    bool transformChanged = !mTransform.FuzzyEqual(GetTransformForInvalidation(mLayer)) ||
                             mLayer->GetPostXScale() != mPostXScale ||
                             mLayer->GetPostYScale() != mPostYScale;
    const Maybe<ParentLayerIntRect>& otherClip = mLayer->GetLocalClipRect();
    nsIntRegion result;

    bool ancestorMaskChanged = mAncestorMaskLayers.Length() != mLayer->GetAncestorMaskLayerCount();
    if (!ancestorMaskChanged) {
      for (size_t i = 0; i < mAncestorMaskLayers.Length(); i++) {
        if (mLayer->GetAncestorMaskLayerAt(i) != mAncestorMaskLayers[i]->mLayer) {
          ancestorMaskChanged = true;
          break;
        }
      }
    }

    // Note that we don't bailout early in general since this function
    // clears some persistent state at the end. Instead we set an overflow
    // flag and check it right before returning.
    bool areaOverflowed = false;

    Layer* otherMask = mLayer->GetMaskLayer();
    if ((mMaskLayer ? mMaskLayer->mLayer : nullptr) != otherMask ||
        ancestorMaskChanged ||
        (mUseClipRect != !!otherClip) ||
        mLayer->GetLocalOpacity() != mOpacity ||
        transformChanged)
    {
      Maybe<IntRect> oldBounds = OldTransformedBounds();
      Maybe<IntRect> newBounds = NewTransformedBounds();
      if (oldBounds && newBounds) {
        LTI_DUMP(oldBounds.value(), "oldtransform");
        LTI_DUMP(newBounds.value(), "newtransform");
        result = oldBounds.value();
        AddRegion(result, newBounds.value());
      } else {
        areaOverflowed = true;
      }

      // We can't bail out early because we need to update mChildrenChanged.
    }

    nsIntRegion internal;
    if (!ComputeChangeInternal(aPrefix, internal, aCallback)) {
      areaOverflowed = true;
    }
    LTI_DUMP(internal, "internal");
    AddRegion(result, internal);
    LTI_DUMP(mLayer->GetInvalidRegion().GetRegion(), "invalid");
    AddTransformedRegion(result, mLayer->GetInvalidRegion().GetRegion(), mTransform);

    if (mMaskLayer && otherMask) {
      nsIntRegion mask;
      if (!mMaskLayer->ComputeChange(aPrefix, mask, aCallback)) {
        areaOverflowed = true;
      }
      LTI_DUMP(mask, "mask");
      AddTransformedRegion(result, mask, mTransform);
    }

    for (size_t i = 0;
         i < std::min(mAncestorMaskLayers.Length(), mLayer->GetAncestorMaskLayerCount());
         i++)
    {
      nsIntRegion mask;
      if (!mAncestorMaskLayers[i]->ComputeChange(aPrefix, mask, aCallback)) {
        areaOverflowed = true;
      }
      LTI_DUMP(mask, "ancestormask");
      AddTransformedRegion(result, mask, mTransform);
    }

    if (mUseClipRect && otherClip) {
      if (!mClipRect.IsEqualInterior(*otherClip)) {
        nsIntRegion tmp;
        tmp.Xor(mClipRect.ToUnknownRect(), otherClip->ToUnknownRect());
        LTI_DUMP(tmp, "clip");
        AddRegion(result, tmp);
      }
    }

    mLayer->ClearInvalidRegion();

    if (areaOverflowed) {
      return false;
    }

    aOutRegion = std::move(result);
    return true;
  }

  void CheckCanary()
  {
    mCanary.Check();
    mLayer->CheckCanary();
  }

  IntRect NewTransformedBoundsForLeaf() {
    return TransformRect(mLayer->GetLocalVisibleRegion().GetBounds().ToUnknownRect(),
                         GetTransformForInvalidation(mLayer));
  }

  IntRect OldTransformedBoundsForLeaf() {
    return TransformRect(mVisibleRegion.GetBounds().ToUnknownRect(), mTransform);
  }

  virtual Maybe<IntRect> NewTransformedBounds()
  {
    return Some(TransformRect(mLayer->GetLocalVisibleRegion().GetBounds().ToUnknownRect(),
                              GetTransformForInvalidation(mLayer)));
  }

  virtual Maybe<IntRect> OldTransformedBounds()
  {
    return Some(TransformRect(mVisibleRegion.GetBounds().ToUnknownRect(), mTransform));
  }

  virtual bool ComputeChangeInternal(const char* aPrefix,
                                     nsIntRegion& aOutRegion,
                                     NotifySubDocInvalidationFunc aCallback)
  {
    if (mLayer->AsHostLayer() && !mLayer->GetLocalVisibleRegion().ToUnknownRegion().IsEqual(mVisibleRegion)) {
      IntRect result = NewTransformedBoundsForLeaf();
      result = result.Union(OldTransformedBoundsForLeaf());
      aOutRegion = result;
    }
    return true;
  }

  RefPtr<Layer> mLayer;
  UniquePtr<LayerPropertiesBase> mMaskLayer;
  nsTArray<UniquePtr<LayerPropertiesBase>> mAncestorMaskLayers;
  nsIntRegion mVisibleRegion;
  Matrix4x4Flagged mTransform;
  float mPostXScale;
  float mPostYScale;
  float mOpacity;
  ParentLayerIntRect mClipRect;
  bool mUseClipRect;
  mozilla::CorruptionCanary mCanary;
};

struct ContainerLayerProperties : public LayerPropertiesBase
{
  explicit ContainerLayerProperties(ContainerLayer* aLayer)
    : LayerPropertiesBase(aLayer)
    , mPreXScale(aLayer->GetPreXScale())
    , mPreYScale(aLayer->GetPreYScale())
  {
    for (Layer* child = aLayer->GetFirstChild(); child; child = child->GetNextSibling()) {
      child->CheckCanary();
      mChildren.AppendElement(CloneLayerTreePropertiesInternal(child));
    }
  }

protected:
  ContainerLayerProperties(const ContainerLayerProperties& a) = delete;
  ContainerLayerProperties& operator=(const ContainerLayerProperties& a) = delete;

public:
  bool ComputeChangeInternal(const char *aPrefix,
                             nsIntRegion& aOutRegion,
                             NotifySubDocInvalidationFunc aCallback) override
  {
    // Make sure we got our virtual call right
    mSubtypeCanary.Check();
    ContainerLayer* container = mLayer->AsContainerLayer();
    nsIntRegion invalidOfLayer; // Invalid regions of this layer.
    nsIntRegion result;         // Invliad regions for children only.

    container->CheckCanary();

    bool childrenChanged = false;
    bool invalidateWholeLayer = false;
    bool areaOverflowed = false;
    if (mPreXScale != container->GetPreXScale() ||
        mPreYScale != container->GetPreYScale())
    {
      Maybe<IntRect> oldBounds = OldTransformedBounds();
      Maybe<IntRect> newBounds = NewTransformedBounds();
      if (oldBounds && newBounds) {
        invalidOfLayer = oldBounds.value();
        AddRegion(invalidOfLayer, newBounds.value());
      } else {
        areaOverflowed = true;
      }
      childrenChanged = true;
      invalidateWholeLayer = true;

      // Can't bail out early, we need to update the child container layers
    }

    // A low frame rate is especially visible to users when scrolling, so we
    // particularly want to avoid unnecessary invalidation at that time. For us
    // here, that means avoiding unnecessary invalidation of child items when
    // other children are added to or removed from our container layer, since
    // that may be caused by children being scrolled in or out of view. We are
    // less concerned with children changing order.
    // TODO: Consider how we could avoid unnecessary invalidation when children
    // change order, and whether the overhead would be worth it.

    nsDataHashtable<nsPtrHashKey<Layer>, uint32_t> oldIndexMap(mChildren.Length());
    for (uint32_t i = 0; i < mChildren.Length(); ++i) {
      mChildren[i]->CheckCanary();
      oldIndexMap.Put(mChildren[i]->mLayer, i);
    }

    uint32_t i = 0; // cursor into the old child list mChildren
    for (Layer* child = container->GetFirstChild(); child; child = child->GetNextSibling()) {
      bool invalidateChildsCurrentArea = false;
      if (i < mChildren.Length()) {
        uint32_t childsOldIndex;
        if (oldIndexMap.Get(child, &childsOldIndex)) {
          if (childsOldIndex >= i) {
            // Invalidate the old areas of layers that used to be between the
            // current |child| and the previous |child| that was also in the
            // old list mChildren (if any of those children have been reordered
            // rather than removed, we will invalidate their new area when we
            // encounter them in the new list):
            for (uint32_t j = i; j < childsOldIndex; ++j) {
              if (Maybe<IntRect> bounds = mChildren[j]->OldTransformedBounds()) {
                LTI_DUMP(bounds.value(), "reordered child");
                AddRegion(result, bounds.value());
              } else {
                areaOverflowed = true;
              }
              childrenChanged |= true;
            }
            if (childsOldIndex >= mChildren.Length()) {
              MOZ_CRASH("Out of bounds");
            }
            // Invalidate any regions of the child that have changed:
            nsIntRegion region;
            if (!mChildren[childsOldIndex]->ComputeChange(LTI_DEEPER(aPrefix), region, aCallback)) {
              areaOverflowed = true;
            }
            i = childsOldIndex + 1;
            if (!region.IsEmpty()) {
              LTI_LOG("%s%p: child %p produced %s\n", aPrefix, mLayer.get(),
                mChildren[childsOldIndex]->mLayer.get(), Stringify(region).c_str());
              AddRegion(result, region);
              childrenChanged |= true;
            }
          } else {
            // We've already seen this child in mChildren (which means it must
            // have been reordered) and invalidated its old area. We need to
            // invalidate its new area too:
            invalidateChildsCurrentArea = true;
          }
        } else {
          // |child| is new
          invalidateChildsCurrentArea = true;
        }
      } else {
        // |child| is new, or was reordered to a higher index
        invalidateChildsCurrentArea = true;
      }
      if (invalidateChildsCurrentArea) {
        LTI_DUMP(child->GetLocalVisibleRegion().ToUnknownRegion(), "invalidateChildsCurrentArea");
        AddTransformedRegion(result, child->GetLocalVisibleRegion().ToUnknownRegion(),
                             GetTransformForInvalidation(child));
        if (aCallback) {
          NotifySubdocumentInvalidation(child, aCallback);
        } else {
          ClearInvalidations(child);
        }
      }
      childrenChanged |= invalidateChildsCurrentArea;
    }

    // Process remaining removed children.
    while (i < mChildren.Length()) {
      childrenChanged |= true;
      if (Maybe<IntRect> bounds = mChildren[i]->OldTransformedBounds()) {
        LTI_DUMP(bounds.value(), "removed child");
        AddRegion(result, bounds.value());
      } else {
        areaOverflowed = true;
      }
      i++;
    }

    if (aCallback) {
      aCallback(container, areaOverflowed ? nullptr : &result);
    }

    if (childrenChanged || areaOverflowed) {
      container->SetChildrenChanged(true);
    }

    if (container->UseIntermediateSurface()) {
      Maybe<IntRect> bounds;
      if (!invalidateWholeLayer && !areaOverflowed) {
        bounds = Some(result.GetBounds());

        // Process changes in the visible region.
        IntRegion newVisible = mLayer->GetLocalVisibleRegion().ToUnknownRegion();
        if (!newVisible.IsEqual(mVisibleRegion)) {
          newVisible.XorWith(mVisibleRegion);
          bounds = bounds->SafeUnion(newVisible.GetBounds());
        }
      }
      container->SetInvalidCompositeRect(bounds ? bounds.ptr() : nullptr);
    }

    // Safe to bail out early now, persistent state has been set.
    if (areaOverflowed) {
      return false;
    }

    if (!mLayer->Extend3DContext()) {
      // |result| contains invalid regions only of children.
      result.Transform(GetTransformForInvalidation(mLayer).GetMatrix());
    }
    // else, effective transforms have applied on children.

    LTI_DUMP(invalidOfLayer, "invalidOfLayer");
    result.OrWith(invalidOfLayer);

    aOutRegion = std::move(result);
    return true;
  }

  Maybe<IntRect> NewTransformedBounds() override
  {
    if (mLayer->Extend3DContext()) {
      IntRect result;
      for (UniquePtr<LayerPropertiesBase>& child : mChildren) {
        Maybe<IntRect> childBounds = child->NewTransformedBounds();
        if (!childBounds) {
          return Nothing();
        }
        Maybe<IntRect> combined = result.SafeUnion(childBounds.value());
        if (!combined) {
          LTI_LOG("overflowed bounds of container %p accumulating child %p\n", this, child->mLayer);
          return Nothing();
        }
        result = combined.value();
      }
      return Some(result);
    }

    return LayerPropertiesBase::NewTransformedBounds();
  }

  Maybe<IntRect> OldTransformedBounds() override
  {
    if (mLayer->Extend3DContext()) {
      IntRect result;
      for (UniquePtr<LayerPropertiesBase>& child : mChildren) {
        Maybe<IntRect> childBounds = child->OldTransformedBounds();
        if (!childBounds) {
          return Nothing();
        }
        Maybe<IntRect> combined = result.SafeUnion(childBounds.value());
        if (!combined) {
          LTI_LOG("overflowed bounds of container %p accumulating child %p\n", this, child->mLayer);
          return Nothing();
        }
        result = combined.value();
      }
      return Some(result);
    }
    return LayerPropertiesBase::OldTransformedBounds();
  }

  // The old list of children:
  mozilla::CorruptionCanary mSubtypeCanary;
  nsTArray<UniquePtr<LayerPropertiesBase>> mChildren;
  float mPreXScale;
  float mPreYScale;
};

struct ColorLayerProperties : public LayerPropertiesBase
{
  explicit ColorLayerProperties(ColorLayer *aLayer)
    : LayerPropertiesBase(aLayer)
    , mColor(aLayer->GetColor())
    , mBounds(aLayer->GetBounds())
  { }

protected:
  ColorLayerProperties(const ColorLayerProperties& a) = delete;
  ColorLayerProperties& operator=(const ColorLayerProperties& a) = delete;

public:
  bool ComputeChangeInternal(const char* aPrefix,
                             nsIntRegion& aOutRegion,
                             NotifySubDocInvalidationFunc aCallback) override
  {
    ColorLayer* color = static_cast<ColorLayer*>(mLayer.get());

    if (mColor != color->GetColor()) {
      LTI_DUMP(NewTransformedBoundsForLeaf(), "color");
      aOutRegion = NewTransformedBoundsForLeaf();
      return true;
    }

    nsIntRegion boundsDiff;
    boundsDiff.Xor(mBounds, color->GetBounds());
    LTI_DUMP(boundsDiff, "colorbounds");

    AddTransformedRegion(aOutRegion, boundsDiff, mTransform);
    return true;
  }

  Color mColor;
  IntRect mBounds;
};

static ImageHost* GetImageHost(Layer* aLayer)
{
  HostLayer* compositor = aLayer->AsHostLayer();
  if (compositor) {
    return static_cast<ImageHost*>(compositor->GetCompositableHost());
  }
  return nullptr;
}

struct ImageLayerProperties : public LayerPropertiesBase
{
  explicit ImageLayerProperties(ImageLayer* aImage, bool aIsMask)
    : LayerPropertiesBase(aImage)
    , mContainer(aImage->GetContainer())
    , mImageHost(GetImageHost(aImage))
    , mSamplingFilter(aImage->GetSamplingFilter())
    , mScaleToSize(aImage->GetScaleToSize())
    , mScaleMode(aImage->GetScaleMode())
    , mLastProducerID(-1)
    , mLastFrameID(-1)
    , mIsMask(aIsMask)
  {
    if (mImageHost) {
      mLastProducerID = mImageHost->GetLastProducerID();
      mLastFrameID = mImageHost->GetLastFrameID();
    }
  }

  bool ComputeChangeInternal(const char* aPrefix,
                             nsIntRegion& aOutRegion,
                             NotifySubDocInvalidationFunc aCallback) override
  {
    ImageLayer* imageLayer = static_cast<ImageLayer*>(mLayer.get());

    if (!imageLayer->GetLocalVisibleRegion().ToUnknownRegion().IsEqual(mVisibleRegion)) {
      IntRect result = NewTransformedBoundsForLeaf();
      result = result.Union(OldTransformedBoundsForLeaf());
      aOutRegion = result;
      return true;
    }

    ImageContainer* container = imageLayer->GetContainer();
    ImageHost* host = GetImageHost(imageLayer);
    if (mContainer != container ||
        mSamplingFilter != imageLayer->GetSamplingFilter() ||
        mScaleToSize != imageLayer->GetScaleToSize() ||
        mScaleMode != imageLayer->GetScaleMode() ||
        host != mImageHost ||
        (host && host->GetProducerID() != mLastProducerID) ||
        (host && host->GetFrameID() != mLastFrameID)) {

      if (mIsMask) {
        // Mask layers have an empty visible region, so we have to
        // use the image size instead.
        IntSize size;
        if (container) {
          size = container->GetCurrentSize();
        }
        if (host) {
          size = host->GetImageSize();
        }
        IntRect rect(0, 0, size.width, size.height);
        LTI_DUMP(rect, "mask");
        aOutRegion = TransformRect(rect, GetTransformForInvalidation(mLayer));
        return true;
      }
      LTI_DUMP(NewTransformedBoundsForLeaf(), "bounds");
      aOutRegion = NewTransformedBoundsForLeaf();
      return true;
    }

    return true;
  }

  RefPtr<ImageContainer> mContainer;
  RefPtr<ImageHost> mImageHost;
  SamplingFilter mSamplingFilter;
  gfx::IntSize mScaleToSize;
  ScaleMode mScaleMode;
  int32_t mLastProducerID;
  int32_t mLastFrameID;
  bool mIsMask;
};

struct CanvasLayerProperties : public LayerPropertiesBase
{
  explicit CanvasLayerProperties(CanvasLayer* aCanvas)
    : LayerPropertiesBase(aCanvas)
    , mImageHost(GetImageHost(aCanvas))
  {
    mFrameID = mImageHost ? mImageHost->GetFrameID() : -1;
  }

  bool ComputeChangeInternal(const char* aPrefix,
                             nsIntRegion& aOutRegion,
                             NotifySubDocInvalidationFunc aCallback) override
  {
    CanvasLayer* canvasLayer = static_cast<CanvasLayer*>(mLayer.get());

    ImageHost* host = GetImageHost(canvasLayer);
    if (host && host->GetFrameID() != mFrameID) {
      LTI_DUMP(NewTransformedBoundsForLeaf(), "frameId");
      aOutRegion = NewTransformedBoundsForLeaf();
      return true;
    }

    return true;
  }

  RefPtr<ImageHost> mImageHost;
  int32_t mFrameID;
};

UniquePtr<LayerPropertiesBase>
CloneLayerTreePropertiesInternal(Layer* aRoot, bool aIsMask /* = false */)
{
  if (!aRoot) {
    return MakeUnique<LayerPropertiesBase>();
  }

  MOZ_ASSERT(!aIsMask || aRoot->GetType() == Layer::TYPE_IMAGE);

  aRoot->CheckCanary();

  switch (aRoot->GetType()) {
    case Layer::TYPE_CONTAINER:
    case Layer::TYPE_REF:
      return MakeUnique<ContainerLayerProperties>(aRoot->AsContainerLayer());
    case Layer::TYPE_COLOR:
      return MakeUnique<ColorLayerProperties>(static_cast<ColorLayer*>(aRoot));
    case Layer::TYPE_IMAGE:
      return MakeUnique<ImageLayerProperties>(static_cast<ImageLayer*>(aRoot), aIsMask);
    case Layer::TYPE_CANVAS:
      return MakeUnique<CanvasLayerProperties>(static_cast<CanvasLayer*>(aRoot));
    case Layer::TYPE_DISPLAYITEM:
    case Layer::TYPE_READBACK:
    case Layer::TYPE_SHADOW:
    case Layer::TYPE_PAINTED:
      return MakeUnique<LayerPropertiesBase>(aRoot);
  }

  MOZ_ASSERT_UNREACHABLE("Unexpected root layer type");
  return MakeUnique<LayerPropertiesBase>(aRoot);
}

/* static */ UniquePtr<LayerProperties>
LayerProperties::CloneFrom(Layer* aRoot)
{
  return CloneLayerTreePropertiesInternal(aRoot);
}

/* static */ void
LayerProperties::ClearInvalidations(Layer *aLayer)
{
  ForEachNode<ForwardIterator>(
        aLayer,
        [] (Layer* layer)
        {
          layer->ClearInvalidRegion();
          if (layer->GetMaskLayer()) {
            ClearInvalidations(layer->GetMaskLayer());
          }
          for (size_t i = 0; i < layer->GetAncestorMaskLayerCount(); i++) {
            ClearInvalidations(layer->GetAncestorMaskLayerAt(i));
          }

        }
      );
}

bool
LayerPropertiesBase::ComputeDifferences(Layer* aRoot, nsIntRegion& aOutRegion, NotifySubDocInvalidationFunc aCallback)
{
  NS_ASSERTION(aRoot, "Must have a layer tree to compare against!");
  if (mLayer != aRoot) {
    if (aCallback) {
      NotifySubdocumentInvalidation(aRoot, aCallback);
    } else {
      ClearInvalidations(aRoot);
    }
    IntRect bounds = TransformRect(
      aRoot->GetLocalVisibleRegion().GetBounds().ToUnknownRect(),
      aRoot->GetLocalTransform());
    Maybe<IntRect> oldBounds = OldTransformedBounds();
    if (!oldBounds) {
      return false;
    }
    Maybe<IntRect> result = bounds.SafeUnion(oldBounds.value());
    if (!result) {
      LTI_LOG("overflowed bounds computing the union of layers %p and %p\n", mLayer.get(), aRoot);
      return false;
    }
    aOutRegion = result.value();
    return true;
  }
  return ComputeChange("  ", aOutRegion, aCallback);
}

void
LayerPropertiesBase::MoveBy(const IntPoint& aOffset)
{
  mTransform.PostTranslate(aOffset.x, aOffset.y, 0);
}

} // namespace layers
} // namespace mozilla