dom/canvas/OffscreenCanvasDisplayHelper.cpp

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* 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 "OffscreenCanvasDisplayHelper.h"
#include "mozilla/gfx/2D.h"
#include "mozilla/gfx/CanvasManagerChild.h"
#include "mozilla/gfx/Swizzle.h"
#include "mozilla/layers/ImageBridgeChild.h"
#include "mozilla/layers/TextureClientSharedSurface.h"
#include "mozilla/layers/TextureWrapperImage.h"
#include "mozilla/SVGObserverUtils.h"
#include "nsICanvasRenderingContextInternal.h"

namespace mozilla::dom {

OffscreenCanvasDisplayHelper::OffscreenCanvasDisplayHelper(
    HTMLCanvasElement* aCanvasElement, uint32_t aWidth, uint32_t aHeight)
    : mMutex("mozilla::dom::OffscreenCanvasDisplayHelper"),
      mCanvasElement(aCanvasElement),
      mImageProducerID(layers::ImageContainer::AllocateProducerID()) {
  mData.mSize.width = aWidth;
  mData.mSize.height = aHeight;
}

OffscreenCanvasDisplayHelper::~OffscreenCanvasDisplayHelper() = default;

void OffscreenCanvasDisplayHelper::Destroy() {
  MOZ_ASSERT(NS_IsMainThread());

  MutexAutoLock lock(mMutex);
  mCanvasElement = nullptr;
}

CanvasContextType OffscreenCanvasDisplayHelper::GetContextType() const {
  MutexAutoLock lock(mMutex);
  return mType;
}

RefPtr<layers::ImageContainer> OffscreenCanvasDisplayHelper::GetImageContainer()
    const {
  MutexAutoLock lock(mMutex);
  return mImageContainer;
}

void OffscreenCanvasDisplayHelper::UpdateContext(
    CanvasContextType aType, const Maybe<int32_t>& aChildId) {
  MutexAutoLock lock(mMutex);
  mImageContainer =
      MakeRefPtr<layers::ImageContainer>(layers::ImageContainer::ASYNCHRONOUS);
  mType = aType;
  mContextChildId = aChildId;

  if (aChildId) {
    mContextManagerId = Some(gfx::CanvasManagerChild::Get()->Id());
  } else {
    mContextManagerId.reset();
  }

  MaybeQueueInvalidateElement();
}

bool OffscreenCanvasDisplayHelper::CommitFrameToCompositor(
    nsICanvasRenderingContextInternal* aContext,
    layers::TextureType aTextureType,
    const Maybe<OffscreenCanvasDisplayData>& aData) {
  MutexAutoLock lock(mMutex);

  gfx::SurfaceFormat format = gfx::SurfaceFormat::B8G8R8A8;
  layers::TextureFlags flags = layers::TextureFlags::IMMUTABLE;

  if (!mCanvasElement) {
    // Our weak reference to the canvas element has been cleared, so we cannot
    // present directly anymore.
    return false;
  }

  if (aData) {
    mData = aData.ref();
    MaybeQueueInvalidateElement();
  }

  if (mData.mIsOpaque) {
    flags |= layers::TextureFlags::IS_OPAQUE;
    format = gfx::SurfaceFormat::B8G8R8X8;
  } else if (!mData.mIsAlphaPremult) {
    flags |= layers::TextureFlags::NON_PREMULTIPLIED;
  }

  switch (mData.mOriginPos) {
    case gl::OriginPos::BottomLeft:
      flags |= layers::TextureFlags::ORIGIN_BOTTOM_LEFT;
      break;
    case gl::OriginPos::TopLeft:
      break;
    default:
      MOZ_ASSERT_UNREACHABLE("Unhandled origin position!");
      break;
  }

  auto imageBridge = layers::ImageBridgeChild::GetSingleton();
  if (!imageBridge) {
    return false;
  }

  if (mData.mDoPaintCallbacks) {
    aContext->OnBeforePaintTransaction();
  }

  RefPtr<layers::Image> image;
  RefPtr<gfx::SourceSurface> surface;

  Maybe<layers::SurfaceDescriptor> desc =
      aContext->PresentFrontBuffer(nullptr, aTextureType);
  if (desc) {
    RefPtr<layers::TextureClient> texture =
        layers::SharedSurfaceTextureData::CreateTextureClient(
            *desc, format, mData.mSize, flags, imageBridge);
    if (texture) {
      image = new layers::TextureWrapperImage(
          texture, gfx::IntRect(gfx::IntPoint(0, 0), mData.mSize));
    }
  } else {
    surface = aContext->GetFrontBufferSnapshot(/* requireAlphaPremult */ false);
    if (surface) {
      auto surfaceImage = MakeRefPtr<layers::SourceSurfaceImage>(surface);
      surfaceImage->SetTextureFlags(flags);
      image = surfaceImage;
    }
  }

  if (mData.mDoPaintCallbacks) {
    aContext->OnDidPaintTransaction();
  }

  if (image) {
    AutoTArray<layers::ImageContainer::NonOwningImage, 1> imageList;
    imageList.AppendElement(layers::ImageContainer::NonOwningImage(
        image, TimeStamp(), mLastFrameID++, mImageProducerID));
    mImageContainer->SetCurrentImages(imageList);
  } else {
    mImageContainer->ClearAllImages();
  }

  // We save the current surface because we might need it in GetSnapshot. If we
  // are on a worker thread and not WebGL, then this will be the only way we can
  // access the pixel data on the main thread.
  mFrontBufferSurface = surface;
  return true;
}

void OffscreenCanvasDisplayHelper::MaybeQueueInvalidateElement() {
  mMutex.AssertCurrentThreadOwns();

  if (!mPendingInvalidate) {
    mPendingInvalidate = true;
    NS_DispatchToMainThread(NS_NewRunnableFunction(
        "OffscreenCanvasDisplayHelper::InvalidateElement",
        [self = RefPtr{this}] { self->InvalidateElement(); }));
  }
}

void OffscreenCanvasDisplayHelper::InvalidateElement() {
  MOZ_ASSERT(NS_IsMainThread());

  HTMLCanvasElement* canvasElement;
  gfx::IntSize size;

  {
    MutexAutoLock lock(mMutex);
    MOZ_ASSERT(mPendingInvalidate);
    mPendingInvalidate = false;
    canvasElement = mCanvasElement;
    size = mData.mSize;
  }

  if (canvasElement) {
    SVGObserverUtils::InvalidateDirectRenderingObservers(canvasElement);
    canvasElement->InvalidateCanvasPlaceholder(size.width, size.height);
    canvasElement->InvalidateCanvasContent(nullptr);
  }
}

bool OffscreenCanvasDisplayHelper::TransformSurface(
    const gfx::DataSourceSurface::ScopedMap& aSrcMap,
    const gfx::DataSourceSurface::ScopedMap& aDstMap,
    gfx::SurfaceFormat aFormat, const gfx::IntSize& aSize, bool aNeedsPremult,
    gl::OriginPos aOriginPos) const {
  if (!aSrcMap.IsMapped() || !aDstMap.IsMapped()) {
    return false;
  }

  switch (aOriginPos) {
    case gl::OriginPos::BottomLeft:
      if (aNeedsPremult) {
        return gfx::PremultiplyYFlipData(aSrcMap.GetData(), aSrcMap.GetStride(),
                                         aFormat, aDstMap.GetData(),
                                         aDstMap.GetStride(), aFormat, aSize);
      }
      return gfx::SwizzleYFlipData(aSrcMap.GetData(), aSrcMap.GetStride(),
                                   aFormat, aDstMap.GetData(),
                                   aDstMap.GetStride(), aFormat, aSize);
    case gl::OriginPos::TopLeft:
      if (aNeedsPremult) {
        return gfx::PremultiplyData(aSrcMap.GetData(), aSrcMap.GetStride(),
                                    aFormat, aDstMap.GetData(),
                                    aDstMap.GetStride(), aFormat, aSize);
      }
      return gfx::SwizzleData(aSrcMap.GetData(), aSrcMap.GetStride(), aFormat,
                              aDstMap.GetData(), aDstMap.GetStride(), aFormat,
                              aSize);
    default:
      MOZ_ASSERT_UNREACHABLE("Unhandled origin position!");
      break;
  }

  return false;
}

already_AddRefed<gfx::SourceSurface>
OffscreenCanvasDisplayHelper::GetSurfaceSnapshot() {
  MOZ_ASSERT(NS_IsMainThread());

  Maybe<layers::SurfaceDescriptor> desc;

  bool hasAlpha;
  bool isAlphaPremult;
  gl::OriginPos originPos;
  Maybe<uint32_t> managerId;
  Maybe<int32_t> childId;
  HTMLCanvasElement* canvasElement;
  RefPtr<gfx::SourceSurface> surface;

  {
    MutexAutoLock lock(mMutex);
    hasAlpha = !mData.mIsOpaque;
    isAlphaPremult = mData.mIsAlphaPremult;
    originPos = mData.mOriginPos;
    managerId = mContextManagerId;
    childId = mContextChildId;
    canvasElement = mCanvasElement;
    surface = mFrontBufferSurface;
  }

  if (surface) {
    // We already have a copy of the front buffer in our process.

    if (originPos == gl::OriginPos::TopLeft && (!hasAlpha || isAlphaPremult)) {
      // If we don't need to y-flip, and it is either opaque or premultiplied,
      // we can just return the same surface.
      return surface.forget();
    }

    // Otherwise we need to copy and apply the necessary transformations.
    RefPtr<gfx::DataSourceSurface> srcSurface = surface->GetDataSurface();
    if (!srcSurface) {
      return nullptr;
    }

    const auto size = srcSurface->GetSize();
    const auto format = srcSurface->GetFormat();

    RefPtr<gfx::DataSourceSurface> dstSurface =
        gfx::Factory::CreateDataSourceSurface(size, format, /* aZero */ false);
    if (!dstSurface) {
      return nullptr;
    }

    gfx::DataSourceSurface::ScopedMap srcMap(srcSurface,
                                             gfx::DataSourceSurface::READ);
    gfx::DataSourceSurface::ScopedMap dstMap(dstSurface,
                                             gfx::DataSourceSurface::WRITE);
    if (!TransformSurface(srcMap, dstMap, format, size,
                          hasAlpha && !isAlphaPremult, originPos)) {
      return nullptr;
    }

    return dstSurface.forget();
  }

#ifdef MOZ_WIDGET_ANDROID
  // On Android, we cannot both display a GL context and read back the pixels.
  if (canvasElement) {
    return nullptr;
  }
#endif

  if (managerId && childId) {
    // We don't have a usable surface, and the context lives in the compositor
    // process.
    return gfx::CanvasManagerChild::Get()->GetSnapshot(
        managerId.value(), childId.value(), hasAlpha);
  }

  // If we don't have any protocol IDs, or an existing surface, it is possible
  // it is a main thread OffscreenCanvas instance. If so, then the element's
  // OffscreenCanvas is not neutered and has access to the context. We can use
  // that to get the snapshot directly.
  if (!canvasElement) {
    return nullptr;
  }

  const auto* offscreenCanvas = canvasElement->GetOffscreenCanvas();
  nsICanvasRenderingContextInternal* context = offscreenCanvas->GetContext();
  if (!context) {
    return nullptr;
  }

  surface = context->GetFrontBufferSnapshot(/* requireAlphaPremult */ false);
  if (!surface) {
    return nullptr;
  }

  if (originPos == gl::OriginPos::TopLeft && (!hasAlpha || isAlphaPremult)) {
    // If we don't need to y-flip, and it is either opaque or premultiplied,
    // we can just return the same surface.
    return surface.forget();
  }

  // Otherwise we need to apply the necessary transformations in place.
  RefPtr<gfx::DataSourceSurface> dataSurface = surface->GetDataSurface();
  if (!dataSurface) {
    return nullptr;
  }

  gfx::DataSourceSurface::ScopedMap map(dataSurface,
                                        gfx::DataSourceSurface::READ_WRITE);
  if (!TransformSurface(map, map, dataSurface->GetFormat(),
                        dataSurface->GetSize(), hasAlpha && !isAlphaPremult,
                        originPos)) {
    return nullptr;
  }

  return surface.forget();
}

already_AddRefed<layers::Image> OffscreenCanvasDisplayHelper::GetAsImage() {
  MOZ_ASSERT(NS_IsMainThread());

  RefPtr<gfx::SourceSurface> surface = GetSurfaceSnapshot();
  if (!surface) {
    return nullptr;
  }
  return MakeAndAddRef<layers::SourceSurfaceImage>(surface);
}

}  // namespace mozilla::dom