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, 6 insertions, 1 deletions

diff --git a/core/java/android/view/HardwareRenderer.java b/core/java/android/view/HardwareRenderer.java
index ec1695e..59f941d 100644
--- a/core/java/android/view/HardwareRenderer.java
+++ b/core/java/android/view/HardwareRenderer.java
@@ -1200,7 +1200,12 @@ public abstract class HardwareRenderer {
                             Trace.traceEnd(Trace.TRACE_TAG_VIEW);
                         }
 
-                        status = onPreDraw(dirty);
+                        Trace.traceBegin(Trace.TRACE_TAG_VIEW, "prepareFrame");
+                        try {
+                            status = onPreDraw(dirty);
+                        } finally {
+                            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
+                        }
                         saveCount = canvas.save();
                         callbacks.onHardwarePreDraw(canvas);