Bug 1573343 - Move draw target clearing out of GetBackBufferDrawTarget. r=mattwoodrow

On Windows, where the DrawTarget is rewrapped in a Cairo/pixman DrawTarget,
this will now cause Cairo/pixman to be used for the clear.

Differential Revision: https://phabricator.services.mozilla.com/D41673

--HG--
extra : moz-landing-system : lando

gfx/layers/basic/BasicCompositor.cpp

@@ -305,9 +305,10 @@ BasicCompositor::CreateRenderTargetForWindow(
   RefPtr<BasicCompositingRenderTarget> rt;
   IntRect rect = aRect.ToUnknownRect();
 
+  bool isCleared = false;
   if (aBufferMode != BufferMode::BUFFER_NONE) {
     RefPtr<DrawTarget> target =
-        mWidget->GetBackBufferDrawTarget(mDrawTarget, aRect, aClearRect);
+        mWidget->GetBackBufferDrawTarget(mDrawTarget, aRect, &isCleared);
     if (!target) {
       return nullptr;
     }
@@ -320,10 +321,10 @@ BasicCompositor::CreateRenderTargetForWindow(
       windowRect.ExpandToEnclose(IntPoint(0, 0));
     }
     rt = new BasicCompositingRenderTarget(mDrawTarget, windowRect);
-    if (!aClearRect.IsEmpty()) {
-      IntRect clearRect = aClearRect.ToUnknownRect();
-      mDrawTarget->ClearRect(Rect(clearRect - rt->GetOrigin()));
-    }
+  }
+  if (!aClearRect.IsEmpty() && !isCleared) {
+    gfx::IntRect clearRect = aClearRect.ToUnknownRect() - rt->GetOrigin();
+    rt->mDrawTarget->ClearRect(gfx::Rect(clearRect));
   }
 
   return rt.forget();

widget/CompositorWidget.cpp

@@ -23,7 +23,7 @@ void CompositorWidget::CleanupRemoteDrawing() { mLastBackBuffer = nullptr; }
 
 already_AddRefed<gfx::DrawTarget> CompositorWidget::GetBackBufferDrawTarget(
     gfx::DrawTarget* aScreenTarget, const LayoutDeviceIntRect& aRect,
-    const LayoutDeviceIntRect& aClearRect) {
+    bool* aOutIsCleared) {
   MOZ_ASSERT(aScreenTarget);
   gfx::SurfaceFormat format =
       aScreenTarget->GetFormat() == gfx::SurfaceFormat::B8G8R8X8
@@ -32,24 +32,17 @@ already_AddRefed<gfx::DrawTarget> CompositorWidget::GetBackBufferDrawTarget(
   gfx::IntSize size = aRect.ToUnknownRect().Size();
   gfx::IntSize clientSize = Max(size, GetClientSize().ToUnknownSize());
 
-  RefPtr<gfx::DrawTarget> target;
+  *aOutIsCleared = false;
   // Re-use back buffer if possible
-  if (mLastBackBuffer &&
-      mLastBackBuffer->GetBackendType() == aScreenTarget->GetBackendType() &&
-      mLastBackBuffer->GetFormat() == format &&
-      mLastBackBuffer->GetSize() == clientSize) {
-    target = mLastBackBuffer;
-    if (!aClearRect.IsEmpty()) {
-      gfx::IntRect clearRect =
-          aClearRect.ToUnknownRect() - aRect.ToUnknownRect().TopLeft();
-      target->ClearRect(gfx::Rect(clearRect.X(), clearRect.Y(),
-                                  clearRect.Width(), clearRect.Height()));
-    }
-  } else {
-    target = aScreenTarget->CreateSimilarDrawTarget(clientSize, format);
-    mLastBackBuffer = target;
+  if (!mLastBackBuffer ||
+      mLastBackBuffer->GetBackendType() != aScreenTarget->GetBackendType() ||
+      mLastBackBuffer->GetFormat() != format ||
+      mLastBackBuffer->GetSize() != clientSize) {
+    mLastBackBuffer =
+        aScreenTarget->CreateSimilarDrawTarget(clientSize, format);
+    *aOutIsCleared = true;
   }
-  return target.forget();
+  return do_AddRef(mLastBackBuffer);
 }
 
 already_AddRefed<gfx::SourceSurface> CompositorWidget::EndBackBufferDrawing() {

widget/CompositorWidget.h

@@ -236,7 +236,7 @@ class CompositorWidget {
    */
   virtual already_AddRefed<gfx::DrawTarget> GetBackBufferDrawTarget(
       gfx::DrawTarget* aScreenTarget, const LayoutDeviceIntRect& aRect,
-      const LayoutDeviceIntRect& aClearRect);
+      bool* aOutIsCleared);
 
   /**
    * Ensure end of composition to back buffer.

widget/windows/WinCompositorWidget.cpp

@@ -158,11 +158,11 @@ bool WinCompositorWidget::NeedsToDeferEndRemoteDrawing() {
 
 already_AddRefed<gfx::DrawTarget> WinCompositorWidget::GetBackBufferDrawTarget(
     gfx::DrawTarget* aScreenTarget, const LayoutDeviceIntRect& aRect,
-    const LayoutDeviceIntRect& aClearRect) {
+    bool* aOutIsCleared) {
   MOZ_ASSERT(!mLockedBackBufferData);
 
   RefPtr<gfx::DrawTarget> target = CompositorWidget::GetBackBufferDrawTarget(
-      aScreenTarget, aRect, aClearRect);
+      aScreenTarget, aRect, aOutIsCleared);
   if (!target) {
     return nullptr;
   }

widget/windows/WinCompositorWidget.h

@@ -67,7 +67,7 @@ class WinCompositorWidget : public CompositorWidget,
   LayoutDeviceIntSize GetClientSize() override;
   already_AddRefed<gfx::DrawTarget> GetBackBufferDrawTarget(
       gfx::DrawTarget* aScreenTarget, const LayoutDeviceIntRect& aRect,
-      const LayoutDeviceIntRect& aClearRect) override;
+      bool* aOutIsCleared) override;
   already_AddRefed<gfx::SourceSurface> EndBackBufferDrawing() override;
   bool InitCompositor(layers::Compositor* aCompositor) override;
   uintptr_t GetWidgetKey() override;