Use SkBitmapCache to optimize readPixels on a texture-backed bitmap

src/core/SkBitmapDevice.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapDevice.h"
 #include "SkConfig8888.h"
 #include "SkDraw.h"
@@ skipping 127 matching lines @@
 void* SkBitmapDevice::onAccessPixels(SkImageInfo* info, size_t* rowBytes) {
     if (fBitmap.getPixels()) {
         *info = fBitmap.info();
         *rowBytes = fBitmap.rowBytes();
         return fBitmap.getPixels();
     }
     return NULL;
 }
 
 #include "SkConfig8888.h"
+#include "SkPixelRef.h"
 
 bool SkBitmapDevice::onWritePixels(const SkImageInfo& srcInfo, const void* srcPixels,
                                    size_t srcRowBytes, int x, int y) {
     // since we don't stop creating un-pixeled devices yet, check for no pixels here
     if (NULL == fBitmap.getPixels()) {
         return false;
     }
 
     const SkImageInfo dstInfo = fBitmap.info().makeWH(srcInfo.width(), srcInfo.height());
 
@@ skipping 96 matching lines @@
             }
             // recompute dst, based on the smaller tmpSrc
             matrix.mapRect(&tmpDst, tmpSrc);
             dstPtr = &tmpDst;
         }
 
         // since we may need to clamp to the borders of the src rect within
         // the bitmap, we extract a subset.
         SkIRect srcIR;
         tmpSrc.roundOut(&srcIR);
-        if (!bitmap.extractSubset(&tmpBitmap, srcIR)) {
-            return;
+        if(bitmap.pixelRef()->getTexture()) {
+            // Accelerated source canvas, don't use extractSubset but readPixels to get the subset.
+            // This way, the pixels are copied in CPU memory instead of GPU memory.
+            bitmap.pixelRef()->readPixels(&tmpBitmap, &srcIR);
+        } else {
+            if (!bitmap.extractSubset(&tmpBitmap, srcIR)) {
+                return;
+            }
         }
         bitmapPtr = &tmpBitmap;
 
         // Since we did an extract, we need to adjust the matrix accordingly
         SkScalar dx = 0, dy = 0;
         if (srcIR.fLeft > 0) {
             dx = SkIntToScalar(srcIR.fLeft);
         }
         if (srcIR.fTop > 0) {
             dy = SkIntToScalar(srcIR.fTop);
@@ skipping 113 matching lines @@
         paint.getStyle() != SkPaint::kFill_Style ||
         !SkXfermode::IsMode(paint.getXfermode(), SkXfermode::kSrcOver_Mode)) {
         // turn off lcd, but turn on kGenA8
         flags->fFlags = paint.getFlags() & ~SkPaint::kLCDRenderText_Flag;
         flags->fFlags |= SkPaint::kGenA8FromLCD_Flag;
         return true;
     }
     // we're cool with the paint as is
     return false;
 }