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, 19 insertions, 4 deletions

diff --git a/libs/hwui/LayerRenderer.cpp b/libs/hwui/LayerRenderer.cpp
index f2e7f66..3484d41 100644
--- a/libs/hwui/LayerRenderer.cpp
+++ b/libs/hwui/LayerRenderer.cpp
@@ -18,6 +18,8 @@
 
 #include <ui/Rect.h>
 
+#include <private/hwui/DrawGlInfo.h>
+
 #include "LayerCache.h"
 #include "LayerRenderer.h"
 #include "Matrix.h"
@@ -41,7 +43,8 @@ void LayerRenderer::setViewport(int width, int height) {
     initViewport(width, height);
 }
 
-int LayerRenderer::prepareDirty(float left, float top, float right, float bottom, bool opaque) {
+status_t LayerRenderer::prepareDirty(float left, float top, float right, float bottom,
+        bool opaque) {
     LAYER_RENDERER_LOGD("Rendering into layer, fbo = %d", mLayer->getFbo());
 
     glBindFramebuffer(GL_FRAMEBUFFER, mLayer->getFbo());
@@ -63,6 +66,20 @@ int LayerRenderer::prepareDirty(float left, float top, float right, float bottom
     return OpenGLRenderer::prepareDirty(dirty.left, dirty.top, dirty.right, dirty.bottom, opaque);
 }
 
+status_t LayerRenderer::clear(float left, float top, float right, float bottom, bool opaque) {
+    if (mLayer->isDirty()) {
+        getCaches().disableScissor();
+        glClear(GL_COLOR_BUFFER_BIT);
+
+        getCaches().resetScissor();
+        mLayer->setDirty(false);
+
+        return DrawGlInfo::kStatusDone;
+    }
+
+    return OpenGLRenderer::clear(left, top, right, bottom, opaque);
+}
+
 void LayerRenderer::finish() {
     OpenGLRenderer::finish();
 
@@ -201,6 +218,7 @@ Layer* LayerRenderer::createLayer(uint32_t width, uint32_t height, bool isOpaque
     layer->setAlpha(255, SkXfermode::kSrcOver_Mode);
     layer->setBlend(!isOpaque);
     layer->setColorFilter(NULL);
+    layer->setDirty(true);
     layer->region.clear();
 
     GLuint previousFbo;
@@ -229,9 +247,6 @@ Layer* LayerRenderer::createLayer(uint32_t width, uint32_t height, bool isOpaque
     glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D,
             layer->getTexture(), 0);
 
-    caches.disableScissor();
-    glClear(GL_COLOR_BUFFER_BIT);
-
     glBindFramebuffer(GL_FRAMEBUFFER, previousFbo);
 
     return layer;