Bug 1254897 - Recycle back buffer in BasicCompositor r=jrmuizel

gfx/layers/basic/BasicCompositor.cpp

@@ -172,7 +172,7 @@ BasicCompositor::CreateRenderTargetForWindow(const LayoutDeviceIntRect& aRect, S
   IntRect rect = aRect.ToUnknownRect();
 
   if (aBufferMode != BufferMode::BUFFER_NONE) {
-    RefPtr<DrawTarget> target = mWidget->CreateBackBufferDrawTarget(mDrawTarget, aRect);
+    RefPtr<DrawTarget> target = mWidget->CreateBackBufferDrawTarget(mDrawTarget, aRect, aInit == INIT_MODE_CLEAR);
     if (!target) {
       return nullptr;
     }

widget/cocoa/nsChildView.mm

@@ -2643,6 +2643,7 @@ nsChildView::StartRemoteDrawingInRegion(LayoutDeviceIntRegion& aInvalidRegion,
   }
 
   aInvalidRegion = mBasicCompositorImage->GetUpdateRegion();
+  *aBufferMode = BufferMode::BUFFER_NONE;
 
   return drawTarget.forget();
 }
@@ -2657,6 +2658,7 @@ nsChildView::EndRemoteDrawing()
 void
 nsChildView::CleanupRemoteDrawing()
 {
+  nsBaseWidget::CleanupRemoteDrawing();
   mBasicCompositorImage = nullptr;
   mCornerMaskImage = nullptr;
   mResizerImage = nullptr;

widget/nsBaseWidget.cpp

@@ -1355,18 +1355,45 @@ CompositorBridgeChild* nsBaseWidget::GetRemoteRenderer()
   return mCompositorBridgeChild;
 }
 
-already_AddRefed<mozilla::gfx::DrawTarget> nsBaseWidget::StartRemoteDrawing()
+already_AddRefed<mozilla::gfx::DrawTarget>
+nsBaseWidget::StartRemoteDrawing()
 {
   return nullptr;
 }
 
+void
+nsBaseWidget::CleanupRemoteDrawing()
+{
+  mLastBackBuffer = nullptr;
+}
+
 already_AddRefed<mozilla::gfx::DrawTarget>
 nsBaseWidget::CreateBackBufferDrawTarget(mozilla::gfx::DrawTarget* aScreenTarget,
-                                         const LayoutDeviceIntRect& aRect)
+                                         const LayoutDeviceIntRect& aRect,
+                                         const bool aInitModeClear)
 {
   MOZ_ASSERT(aScreenTarget);
   gfx::SurfaceFormat format = gfx::SurfaceFormat::B8G8R8A8;
-  return aScreenTarget->CreateSimilarDrawTarget(aRect.ToUnknownRect().Size(), format);
+  gfx::IntSize size = aRect.ToUnknownRect().Size();
+  gfx::IntSize clientSize(GetClientSize().ToUnknownSize());
+
+  RefPtr<gfx::DrawTarget> target;
+  // Re-use back buffer if possible
+  if (mLastBackBuffer &&
+      mLastBackBuffer->GetBackendType() == aScreenTarget->GetBackendType() &&
+      mLastBackBuffer->GetFormat() == format &&
+      size <= mLastBackBuffer->GetSize() &&
+      mLastBackBuffer->GetSize() <= clientSize) {
+    target = mLastBackBuffer;
+    target->SetTransform(gfx::Matrix());
+    if (aInitModeClear) {
+      target->ClearRect(gfx::Rect(0, 0, size.width, size.height));
+    }
+  } else {
+    target = aScreenTarget->CreateSimilarDrawTarget(size, format);
+    mLastBackBuffer = target;
+  }
+  return target.forget();
 }
 
 //-------------------------------------------------------------------------

widget/nsBaseWidget.h

@@ -32,6 +32,10 @@ class Accessible;
 }
 #endif
 
+namespace gfx {
+class DrawTarget;
+} // namespace gfx
+
 namespace layers {
 class BasicLayerManager;
 class CompositorBridgeChild;
@@ -90,6 +94,7 @@ class nsBaseWidget : public nsIWidget, public nsSupportsWeakReference
 
 protected:
   typedef base::Thread Thread;
+  typedef mozilla::gfx::DrawTarget DrawTarget;
   typedef mozilla::layers::BasicLayerManager BasicLayerManager;
   typedef mozilla::layers::BufferMode BufferMode;
   typedef mozilla::layers::CompositorBridgeChild CompositorBridgeChild;
@@ -171,9 +176,10 @@ public:
   virtual void            DrawWindowOverlay(LayerManagerComposite* aManager, LayoutDeviceIntRect aRect) override {}
   virtual already_AddRefed<mozilla::gfx::DrawTarget> StartRemoteDrawing() override;
   virtual void            EndRemoteDrawing() override { };
-  virtual void            CleanupRemoteDrawing() override { };
+  virtual void            CleanupRemoteDrawing() override;
   virtual already_AddRefed<mozilla::gfx::DrawTarget> CreateBackBufferDrawTarget(mozilla::gfx::DrawTarget* aScreenTarget,
-                                                                                const LayoutDeviceIntRect& aRect) override;
+                                                                                const LayoutDeviceIntRect& aRect,
+                                                                                const bool aInitModeClear) override;
   virtual void            UpdateThemeGeometries(const nsTArray<ThemeGeometry>& aThemeGeometries) override {}
   NS_IMETHOD              SetModal(bool aModal) override;
   virtual uint32_t        GetMaxTouchPoints() const override;
@@ -522,6 +528,8 @@ protected:
   RefPtr<mozilla::CompositorVsyncDispatcher> mCompositorVsyncDispatcher;
   RefPtr<APZCTreeManager> mAPZC;
   RefPtr<APZEventState> mAPZEventState;
+  // Back buffer of BasicCompositor
+  RefPtr<DrawTarget> mLastBackBuffer;
   SetAllowedTouchBehaviorCallback mSetAllowedTouchBehaviorCallback;
   RefPtr<WidgetShutdownObserver> mShutdownObserver;
   RefPtr<TextEventDispatcher> mTextEventDispatcher;

widget/nsIWidget.h

@@ -1324,7 +1324,8 @@ class nsIWidget : public nsISupports {
      * Create DrawTarget used as BackBuffer of the screen
      */
     virtual already_AddRefed<mozilla::gfx::DrawTarget> CreateBackBufferDrawTarget(mozilla::gfx::DrawTarget* aScreenTarget,
-                                                                                  const LayoutDeviceIntRect& aRect) = 0;
+                                                                                  const LayoutDeviceIntRect& aRect,
+                                                                                  const bool aInitModeClear) = 0;
 
     /**
      * A hook for the widget to prepare a Compositor, during the latter's initialization.