Bug 953303 - HwcComposer2D should honor HWC_HINT_CLEAR_FB set by hwcomposer. r=ncameron

gfx/layers/Compositor.h

@@ -304,6 +304,11 @@ public:
                          gfx::Float aOpacity, const gfx::Matrix4x4 &aTransform)
   { /* Should turn into pure virtual once implemented in D3D */ }
 
+  /*
+   * Clear aRect on FrameBuffer.
+   */
+  virtual void clearFBRect(const gfx::Rect* aRect) { }
+
   /**
    * Start a new frame.
    *

gfx/layers/composite/ContainerLayerComposite.cpp

@@ -318,6 +318,12 @@ ContainerRender(ContainerT* aContainer,
       // Composer2D will compose this layer so skip GPU composition
       // this time & reset composition flag for next composition phase
       layerToRender->SetLayerComposited(false);
+      if (layerToRender->GetClearFB()) {
+        // Clear layer's visible rect on FrameBuffer with transparent pixels
+        gfx::Rect aRect(clipRect.x, clipRect.y, clipRect.width, clipRect.height);
+        compositor->clearFBRect(&aRect);
+        layerToRender->SetClearFB(false);
+      }
     } else {
       layerToRender->RenderLayer(clipRect);
     }

gfx/layers/composite/LayerManagerComposite.cpp

@@ -764,6 +764,7 @@ LayerComposite::LayerComposite(LayerManagerComposite *aManager)
   , mShadowTransformSetByAnimation(false)
   , mDestroyed(false)
   , mLayerComposited(false)
+  , mClearFB(false)
 { }
 
 LayerComposite::~LayerComposite()

gfx/layers/composite/LayerManagerComposite.h

@@ -358,6 +358,11 @@ public:
     mLayerComposited = value;
   }
 
+  void SetClearFB(bool value)
+  {
+    mClearFB = value;
+  }
+
   // These getters can be used anytime.
   float GetShadowOpacity() { return mShadowOpacity; }
   const nsIntRect* GetShadowClipRect() { return mUseShadowClipRect ? &mShadowClipRect : nullptr; }
@@ -365,6 +370,7 @@ public:
   const gfx3DMatrix& GetShadowTransform() { return mShadowTransform; }
   bool GetShadowTransformSetByAnimation() { return mShadowTransformSetByAnimation; }
   bool HasLayerBeenComposited() { return mLayerComposited; }
+  bool GetClearFB() { return mClearFB; }
 
 protected:
   gfx3DMatrix mShadowTransform;
@@ -377,6 +383,7 @@ protected:
   bool mShadowTransformSetByAnimation;
   bool mDestroyed;
   bool mLayerComposited;
+  bool mClearFB;
 };
 
 

gfx/layers/opengl/CompositorOGL.cpp

@@ -767,6 +767,18 @@ CalculatePOTSize(const IntSize& aSize, GLContext* gl)
   return IntSize(NextPowerOfTwo(aSize.width), NextPowerOfTwo(aSize.height));
 }
 
+void
+CompositorOGL::clearFBRect(const gfx::Rect* aRect)
+{
+  if (!aRect) {
+    return;
+  }
+
+  ScopedScissorRect autoScissorRect(mGLContext, aRect->x, aRect->y, aRect->width, aRect->height);
+  mGLContext->fClearColor(0.0, 0.0, 0.0, 0.0);
+  mGLContext->fClear(LOCAL_GL_COLOR_BUFFER_BIT | LOCAL_GL_DEPTH_BUFFER_BIT);
+}
+
 void
 CompositorOGL::BeginFrame(const nsIntRegion& aInvalidRegion,
                           const Rect *aClipRectIn,

gfx/layers/opengl/CompositorOGL.h

@@ -252,6 +252,11 @@ private:
    */
   bool mFrameInProgress;
 
+  /*
+   * Clear aRect on FrameBuffer.
+   */
+  virtual void clearFBRect(const gfx::Rect* aRect);
+
   /* Start a new frame. If aClipRectIn is null and aClipRectOut is non-null,
    * sets *aClipRectOut to the screen dimensions.
    */

widget/gonk/HwcComposer2D.cpp

@@ -507,6 +507,13 @@ HwcComposer2D::TryHwComposition()
                     // Overlay Composition, set layer composition flag
                     // on mapped LayerComposite to skip GPU composition
                     mHwcLayerMap[k]->SetLayerComposited(true);
+                    if (k && (mList->hwLayers[k].hints & HWC_HINT_CLEAR_FB) &&
+                        (mList->hwLayers[k].blending == HWC_BLENDING_NONE)) {
+                        // Clear visible rect on FB with transparent pixels.
+                        // Never clear the 1st layer since we're guaranteed
+                        // that FB is already cleared.
+                        mHwcLayerMap[k]->SetClearFB(true);
+                    }
                     break;
                 default:
                     break;