Use texture barriers to read directly from the RT

src/gpu/GrTargetCommands.cpp

Index: src/gpu/GrTargetCommands.cpp
diff --git a/src/gpu/GrTargetCommands.cpp b/src/gpu/GrTargetCommands.cpp
index 9b968dc9e73650c0501fd9786a1e0901bcef2e18..fa807251240f5cffe077967cfe950a0efe79d0fa 100644
--- a/src/gpu/GrTargetCommands.cpp
+++ b/src/gpu/GrTargetCommands.cpp
@@ -402,6 +402,10 @@ void GrTargetCommands::CopySurface::execute(GrGpu* gpu, const SetState*) {
     gpu->copySurface(this->dst(), this->src(), fSrcRect, fDstPoint);
 }
 
+void GrTargetCommands::XferBarrier::execute(GrGpu* gpu, const SetState* state) {
+    gpu->setXferBarrier(fBarrierType);
+}
+
 GrTargetCommands::Cmd* GrTargetCommands::recordCopySurface(GrInOrderDrawBuffer* iodb,
                                                            GrSurface* dst,
                                                            GrSurface* src,
@@ -441,6 +445,8 @@ bool GrTargetCommands::setupPipelineAndShouldDraw(GrInOrderDrawBuffer* iodb,
         fPrevState = ss;
         iodb->recordTraceMarkersIfNecessary(ss);
     }
+
+    this->recordXferBarrierIfNecessary(iodb, pipelineInfo);
     return true;
 }
 
@@ -465,6 +471,27 @@ bool GrTargetCommands::setupPipelineAndShouldDraw(GrInOrderDrawBuffer* iodb,
         fPrevState = ss;
         iodb->recordTraceMarkersIfNecessary(ss);
     }
+
+    this->recordXferBarrierIfNecessary(iodb, pipelineInfo);
     return true;
 }
 
+void GrTargetCommands::recordXferBarrierIfNecessary(GrInOrderDrawBuffer* iodb,
+                                                    const GrDrawTarget::PipelineInfo& info) {
+    SkASSERT(fPrevState);
+    const GrXferProcessor& xp = *fPrevState->getXferProcessor();
+    GrRenderTarget* rt = fPrevState->getRenderTarget();
+
+    GrXferBarrierType barrierType;
+    if (!xp.willNeedXferBarrier(rt, *iodb->caps(), &barrierType)) {
+        return;
+    }
+
+    this->closeBatch();
+
+    XferBarrier* xb = GrNEW_APPEND_TO_RECORDER(fCmdBuffer, XferBarrier, ());
+    xb->fBarrierType = barrierType;
+
+    iodb->recordTraceMarkersIfNecessary(xb);
+}
+