Add discard API to SkCanvas, plumb it to glDiscardFramebuffer()

src/gpu/GrInOrderDrawBuffer.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrInOrderDrawBuffer.h"
 
 #include "GrBufferAllocPool.h"
@@ skipping 486 matching lines @@
         SkASSERT(NULL != renderTarget);
     }
     if (NULL == rect) {
         // We could do something smart and remove previous draws and clears to
         // the current render target. If we get that smart we have to make sure
         // those draws aren't read before this clear (render-to-texture).
         r.setLTRB(0, 0, renderTarget->width(), renderTarget->height());
         rect = &r;
     }
     Clear* clr = this->recordClear();
+    GrColorIsPMAssert(color);
     clr->fColor = color;
     clr->fRect = *rect;
     clr->fCanIgnoreRect = canIgnoreRect;
     clr->fRenderTarget = renderTarget;
     renderTarget->ref();
 }
 
+void GrInOrderDrawBuffer::discard(GrRenderTarget* renderTarget) {
+    if (!this->caps()->discardRenderTargetSupport()) {
+        return;
+    }
+    if (NULL == renderTarget) {
+        renderTarget = this->drawState()->getRenderTarget();
+        SkASSERT(NULL != renderTarget);
+    }
+    Clear* clr = this->recordClear();
+    clr->fColor = GrColor_ILLEGAL;
+    clr->fRenderTarget = renderTarget;
+    renderTarget->ref();
+}
+
 void GrInOrderDrawBuffer::reset() {
     SkASSERT(1 == fGeoPoolStateStack.count());
     this->resetVertexSource();
     this->resetIndexSource();
     int numDraws = fDraws.count();
     for (int d = 0; d < numDraws; ++d) {
         // we always have a VB, but not always an IB
         SkASSERT(NULL != fDraws[d].fVertexBuffer);
         fDraws[d].fVertexBuffer->unref();
         SkSafeUnref(fDraws[d].fIndexBuffer);
@@ skipping 99 matching lines @@
                 fStates[currState].restoreTo(&playbackState);
                 ++currState;
                 break;
             case kSetClip_Cmd:
                 clipData.fClipStack = &fClips[currClip];
                 clipData.fOrigin = fClipOrigins[currClip];
                 fDstGpu->setClip(&clipData);
                 ++currClip;
                 break;
             case kClear_Cmd:
-                fDstGpu->clear(&fClears[currClear].fRect,
-                               fClears[currClear].fColor,
-                               fClears[currClear].fCanIgnoreRect,
-                               fClears[currClear].fRenderTarget);
+                if (GrColor_ILLEGAL == fClears[currClear].fColor) {
+                    fDstGpu->discard(fClears[currClear].fRenderTarget);
+                } else {
+                    fDstGpu->clear(&fClears[currClear].fRect,
+                                   fClears[currClear].fColor,
+                                   fClears[currClear].fCanIgnoreRect,
+                                   fClears[currClear].fRenderTarget);
+                }
                 ++currClear;
                 break;
             case kCopySurface_Cmd:
                 fDstGpu->copySurface(fCopySurfaces[currCopySurface].fDst.get(),
                                      fCopySurfaces[currCopySurface].fSrc.get(),
                                      fCopySurfaces[currCopySurface].fSrcRect,
                                      fCopySurfaces[currCopySurface].fDstPoint);
                 ++currCopySurface;
                 break;
         }
@@ skipping 316 matching lines @@
     this->addToCmdBuffer(kCopySurface_Cmd);
     return &fCopySurfaces.push_back();
 }
 
 
 void GrInOrderDrawBuffer::clipWillBeSet(const GrClipData* newClipData) {
     INHERITED::clipWillBeSet(newClipData);
     fClipSet = true;
     fClipProxyState = kUnknown_ClipProxyState;
 }