Make BRD take advantage of zero initialized memory

tools/codec/SkBitmapRegionCanvas.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapRegionCanvas.h"
 #include "SkBitmapRegionDecoderPriv.h"
 #include "SkCanvas.h"
 #include "SkCodecPriv.h"
 
 SkBitmapRegionCanvas::SkBitmapRegionCanvas(SkCodec* decoder)
     : INHERITED(decoder->getInfo().width(), decoder->getInfo().height())
     , fDecoder(decoder)
 {}
 
-bool SkBitmapRegionCanvas::decodeRegion(SkBitmap* bitmap, SkBitmap::Allocator* allocator,
+bool SkBitmapRegionCanvas::decodeRegion(SkBitmap* bitmap, SkBRDAllocator* allocator,
         const SkIRect& desiredSubset, int sampleSize, SkColorType dstColorType,
         bool requireUnpremul) {
     // Reject color types not supported by this method
     if (kIndex_8_SkColorType == dstColorType || kGray_8_SkColorType == dstColorType) {
         SkCodecPrintf("Error: Color type not supported.\n");
         return false;
     }
 
     // Reject requests for unpremultiplied alpha
     if (requireUnpremul) {
@@ skipping 66 matching lines @@
     bitmap->setInfo(dstInfo, dstInfo.minRowBytes());
     if (!bitmap->tryAllocPixels(allocator, nullptr)) {
         SkCodecPrintf("Error: Could not allocate pixels.\n");
         return false;
     }
 
     // Zero the bitmap if the region is not completely within the image.
     // TODO (msarett): Can we make this faster by implementing it to only
     //                 zero parts of the image that we won't overwrite with
     //                 pixels?
-    // TODO (msarett): This could be skipped if memory is zero initialized.
-    //                 This would matter if this code is moved to Android and
-    //                 uses Android bitmaps.
-    if (SubsetType::kPartiallyInside_SubsetType == type) {
+    SkCodec::ZeroInitialized zeroInit = allocator ? allocator->zeroInit() :

[scroggo, 2015/11/10 22:31:14]

It looks like we only care about the variable zeroInit inside the if statement.
how about the following:

if (SubsetType::kPartiallyInside_SubsetType == type) {
  zeroInit = ...
  if (no_zeroInit == zeroInit) {
    bitmap->eraseColor(0);
  }
}

[msarett, 2015/11/10 22:49:59]

Done.

+                SkCodec::kNo_ZeroInitialized;
+    if (SubsetType::kPartiallyInside_SubsetType == type &&
+            SkCodec::kNo_ZeroInitialized == zeroInit) {
         bitmap->eraseColor(0);
     }
 
     // Use a canvas to crop and scale to the destination bitmap
     SkCanvas canvas(*bitmap);
     // TODO (msarett): Maybe we can take advantage of the fact that SkRect uses floats?
     SkRect src = SkRect::MakeXYWH((SkScalar) subset.x(), (SkScalar) 0,
             (SkScalar) subset.width(), (SkScalar) subset.height());
     SkRect dst = SkRect::MakeXYWH((SkScalar) (outX / sampleSize), (SkScalar) (outY / sampleSize),
             (SkScalar) get_scaled_dimension(subset.width(), sampleSize),
@@ skipping 11 matching lines @@
     // SkCanvas does not draw to these color types.
     if (kIndex_8_SkColorType == colorType || kGray_8_SkColorType == colorType) {
         return false;
     }
 
     // FIXME: Call virtual function when it lands.
     SkImageInfo info = SkImageInfo::Make(0, 0, colorType, fDecoder->getInfo().alphaType(),
             fDecoder->getInfo().profileType());
     return conversion_possible(info, fDecoder->getInfo());
 }