Use texture barriers to read directly from the RT

src/gpu/gl/GrGLGpu.cpp

Index: src/gpu/gl/GrGLGpu.cpp
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index 954ecc4f61c3401ba89f753e5323f27e996e217f..f4d926effee8f3bc80b452400ef0c5b9940c6f2c 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -2768,6 +2768,15 @@ bool GrGLGpu::canCopySurface(const GrSurface* dst,
     return false;
 }
 
+void GrGLGpu::setXferBarrier(GrXferBarrierType type) {
+    switch (type) {
+        case kTexture_GrXferBarrierType:
+            SkASSERT(this->caps()->textureBarrierSupport());

[Chris Dalton, 2015/04/17 08:06:05]

I can update this to an if instead of an assert, to protect from Xfer barriers
that request nonsupported barriers.

[bsalomon, 2015/04/21 15:19:27]

I think an assert is fine. Technically a client could derive their own XP
classes, and if that was common it might be nice to fail in a friendlier manner,
but it's not. Asserting seems ok.

+            GL_CALL(TextureBarrier());
+            return;
+    }
+}
+
 void GrGLGpu::didAddGpuTraceMarker() {
     if (this->caps()->gpuTracingSupport()) {
         const GrTraceMarkerSet& markerArray = this->getActiveTraceMarkers();