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

8 files changed, 58 insertions, 13 deletions

diff --git a/libs/hwui/DisplayListRenderer.cpp b/libs/hwui/DisplayListRenderer.cpp
index 589d5c2..81e68bd 100644
--- a/libs/hwui/DisplayListRenderer.cpp
+++ b/libs/hwui/DisplayListRenderer.cpp
@@ -1434,7 +1434,7 @@ void DisplayListRenderer::setViewport(int width, int height) {
     mHeight = height;
 }
 
-int DisplayListRenderer::prepareDirty(float left, float top,
+status_t DisplayListRenderer::prepareDirty(float left, float top,
         float right, float bottom, bool opaque) {
     mSnapshot = new Snapshot(mFirstSnapshot,
             SkCanvas::kMatrix_SaveFlag | SkCanvas::kClip_SaveFlag);
diff --git a/libs/hwui/DisplayListRenderer.h b/libs/hwui/DisplayListRenderer.h
index 2610055..e42def5 100644
--- a/libs/hwui/DisplayListRenderer.h
+++ b/libs/hwui/DisplayListRenderer.h
@@ -550,7 +550,7 @@ public:
     virtual bool isDeferred();
 
     virtual void setViewport(int width, int height);
-    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);
     virtual void finish();
 
     virtual status_t callDrawGLFunction(Functor *functor, Rect& dirty);
diff --git a/libs/hwui/Layer.cpp b/libs/hwui/Layer.cpp
index 882e4bb..1cdc063 100644
--- a/libs/hwui/Layer.cpp
+++ b/libs/hwui/Layer.cpp
@@ -31,6 +31,7 @@ Layer::Layer(const uint32_t layerWidth, const uint32_t layerHeight) {
     meshIndices = NULL;
     meshElementCount = 0;
     cacheable = true;
+    dirty = false;
     textureLayer = false;
     renderTarget = GL_TEXTURE_2D;
     texture.width = layerWidth;
diff --git a/libs/hwui/Layer.h b/libs/hwui/Layer.h
index 448e3da..e1f6a70 100644
--- a/libs/hwui/Layer.h
+++ b/libs/hwui/Layer.h
@@ -162,6 +162,14 @@ struct Layer {
         this->cacheable = cacheable;
     }
 
+    inline bool isDirty() {
+        return dirty;
+    }
+
+    inline void setDirty(bool dirty) {
+        this->dirty = dirty;
+    }
+
     inline bool isTextureLayer() {
         return textureLayer;
     }
@@ -287,6 +295,12 @@ private:
     bool textureLayer;
 
     /**
+     * When set to true, this layer is dirty and should be cleared
+     * before any rendering occurs.
+     */
+    bool dirty;
+
+    /**
      * Indicates the render target.
      */
     GLenum renderTarget;
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;
diff --git a/libs/hwui/LayerRenderer.h b/libs/hwui/LayerRenderer.h
index acedbcc..c44abce 100644
--- a/libs/hwui/LayerRenderer.h
+++ b/libs/hwui/LayerRenderer.h
@@ -48,7 +48,8 @@ public:
     virtual ~LayerRenderer();
 
     virtual void setViewport(int width, int height);
-    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);
+    virtual status_t clear(float left, float top, float right, float bottom, bool opaque);
     virtual void finish();
 
     ANDROID_API static Layer* createTextureLayer(bool isOpaque);
diff --git a/libs/hwui/OpenGLRenderer.cpp b/libs/hwui/OpenGLRenderer.cpp
index b6be5b3..914516c 100644
--- a/libs/hwui/OpenGLRenderer.cpp
+++ b/libs/hwui/OpenGLRenderer.cpp
@@ -165,11 +165,12 @@ void OpenGLRenderer::initViewport(int width, int height) {
     mFirstSnapshot->viewport.set(0, 0, width, height);
 }
 
-int OpenGLRenderer::prepare(bool opaque) {
+status_t OpenGLRenderer::prepare(bool opaque) {
     return prepareDirty(0.0f, 0.0f, mWidth, mHeight, opaque);
 }
 
-int OpenGLRenderer::prepareDirty(float left, float top, float right, float bottom, bool opaque) {
+status_t OpenGLRenderer::prepareDirty(float left, float top, float right, float bottom,
+        bool opaque) {
     mCaches.clearGarbage();
 
     mSnapshot = new Snapshot(mFirstSnapshot,
@@ -203,15 +204,18 @@ int OpenGLRenderer::prepareDirty(float left, float top, float right, float botto
 
     debugOverdraw(true, true);
 
+    return clear(left, top, right, bottom, opaque);
+}
+
+status_t OpenGLRenderer::clear(float left, float top, float right, float bottom, bool opaque) {
     if (!opaque) {
         mCaches.enableScissor();
         mCaches.setScissor(left, mSnapshot->height - bottom, right - left, bottom - top);
         glClear(GL_COLOR_BUFFER_BIT);
         return DrawGlInfo::kStatusDrew;
-    } else {
-        mCaches.resetScissor();
     }
 
+    mCaches.resetScissor();
     return DrawGlInfo::kStatusDone;
 }
 
@@ -743,6 +747,7 @@ bool OpenGLRenderer::createLayer(float left, float top, float right, float botto
             bounds.getWidth() / float(layer->getWidth()), 0.0f);
     layer->setColorFilter(mColorFilter);
     layer->setBlend(true);
+    layer->setDirty(false);
 
     // Save the layer in the snapshot
     mSnapshot->flags |= Snapshot::kFlagIsLayer;
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