use SkMakeBitmapShader to not force copies when possible

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 304 matching lines @@
     } else {
         USE_DRAWBITMAP:
         // We can go faster by just calling drawBitmap, which will concat the
         // matrix with the CTM, and try to call drawSprite if it can. If not,
         // it will make a shader and call drawRect, as we do below.
         draw.drawBitmap(*bitmapPtr, matrix, dstPtr, paint);
         return;
     }
 
     USE_SHADER:
+
+    // Since the shader need only live for our stack-frame, pass in a custom allocator. This
+    // can save malloc calls, and signals to SkMakeBitmapShader to not try to copy the bitmap
+    // if its mutable, since that precaution is not needed (give the short lifetime of the shader).
+    SkTBlitterAllocator allocator;
     // construct a shader, so we can call drawRect with the dst
-    auto s = SkShader::MakeBitmapShader(*bitmapPtr, SkShader::kClamp_TileMode,
-                                        SkShader::kClamp_TileMode, &matrix);
+    auto s = SkMakeBitmapShader(*bitmapPtr, SkShader::kClamp_TileMode, SkShader::kClamp_TileMode,
+                                &matrix, &allocator);
     if (!s) {
         return;
     }
+    // we deliberately add a ref, since the allocator wants to be the last owner
+    s.get()->ref();
 
     SkPaint paintWithShader(paint);
     paintWithShader.setStyle(SkPaint::kFill_Style);
-    paintWithShader.setShader(std::move(s));
+    paintWithShader.setShader(s);
 
     // Call ourself, in case the subclass wanted to share this setup code
     // but handle the drawRect code themselves.
     this->drawRect(draw, *dstPtr, paintWithShader);
 }
 
 void SkBitmapDevice::drawSprite(const SkDraw& draw, const SkBitmap& bitmap,
                                 int x, int y, const SkPaint& paint) {
     draw.drawSprite(bitmap, x, y, paint);
 }
@@ skipping 89 matching lines @@
         paint.getRasterizer() ||
         paint.getPathEffect() ||
         paint.isFakeBoldText() ||
         paint.getStyle() != SkPaint::kFill_Style ||
         !SkXfermode::IsMode(paint.getXfermode(), SkXfermode::kSrcOver_Mode))
     {
         return true;
     }
     return false;
 }