Defer layer rendering to avoid stalls

Bug #7326824

When a layer is taken out of the cache and initialized it gets cleared
to prepare it for future rendering. This triggers the following sequence
of operations:

glBindFramebuffer(layer.fbo)
attach texture storage to FBO
glClear()
glBindFramebuffer(defaultFbo)

The clear forces a resolve on tilers which stalls the CPU for a little
while, thus producing jank during animations. This change moves the
clear to the next frame when we know we will have to execute a resolve
anyway.

Change-Id: Ic1939c25df20ed65a4c48dc81ee549b2cd8b6ec3

1 files changed, 11 insertions, 2 deletions

diff --git a/libs/hwui/OpenGLRenderer.h b/libs/hwui/OpenGLRenderer.h
index a40d69a..c5e4c8e 100644
--- a/libs/hwui/OpenGLRenderer.h
+++ b/libs/hwui/OpenGLRenderer.h
@@ -94,7 +94,7 @@ public:
      *               and will not be cleared. If false, the target surface
      *               will be cleared
      */
-    ANDROID_API int prepare(bool opaque);
+    ANDROID_API status_t prepare(bool opaque);
 
     /**
      * Prepares the renderer to draw a frame. This method must be invoked
@@ -110,7 +110,7 @@ public:
      *               and will not be cleared. If false, the target surface
      *               will be cleared in the specified dirty rectangle
      */
-    virtual int prepareDirty(float left, float top, float right, float bottom, bool opaque);
+    virtual status_t prepareDirty(float left, float top, float right, float bottom, bool opaque);
 
     /**
      * Indicates the end of a frame. This method must be invoked whenever
@@ -270,6 +270,11 @@ protected:
     void initViewport(int width, int height);
 
     /**
+     * Clears the underlying surface if needed.
+     */
+    virtual status_t clear(float left, float top, float right, float bottom, bool opaque);
+
+    /**
      * Call this method after updating a layer during a drawing pass.
      */
     void resumeAfterLayer();
@@ -355,6 +360,10 @@ protected:
         return false;
     }
 
+    Caches& getCaches() {
+        return mCaches;
+    }
+
 private:
     /**
      * Ensures the state of the renderer is the same as the state of