store SkAlphaType inside SkBitmap, on road to support unpremul

src/images/SkImageDecoder_libpng.cpp

Index: src/images/SkImageDecoder_libpng.cpp
diff --git a/src/images/SkImageDecoder_libpng.cpp b/src/images/SkImageDecoder_libpng.cpp
index b6aa329104288aead5ae32f788e0f80b9aba153d..91520f2b7b1375d1e7d2352ad0eaff4bd485d7e5 100644
--- a/src/images/SkImageDecoder_libpng.cpp
+++ b/src/images/SkImageDecoder_libpng.cpp
@@ -437,7 +437,7 @@ bool SkPNGImageDecoder::onDecode(SkStream* sk_stream, SkBitmap* decodedBitmap,
         // return false, since the result will have premultiplied colors.
         return false;
     }
-    decodedBitmap->setIsOpaque(!reallyHasAlpha);
+    decodedBitmap->setAlphaType(reallyHasAlpha ? kPremul_SkAlphaType : kOpaque_SkAlphaType);

[scroggo, 2013/09/30 22:20:04]

This should check this->getRequireUnpremultipliedColors() and set to
kUnpremul_SkAlphaType if reallyHasAlpha.

     return true;
 }
 
@@ -889,7 +889,7 @@ bool SkPNGImageDecoder::onDecodeSubset(SkBitmap* bm, const SkIRect& region) {
     if (0 != theTranspColor) {
         reallyHasAlpha |= substituteTranspColor(&decodedBitmap, theTranspColor);
     }
-    decodedBitmap.setIsOpaque(!reallyHasAlpha);
+    decodedBitmap.setAlphaType(reallyHasAlpha ? kPremul_SkAlphaType : kOpaque_SkAlphaType);

[scroggo, 2013/09/30 22:20:04]

This should also check requireUnpremul

 
     if (swapOnly) {
         bm->swap(decodedBitmap);