Add the method isOpaque() to SkImage

src/image/SkImage_Codec.cpp

Index: src/image/SkImage_Codec.cpp
diff --git a/src/image/SkImage_Codec.cpp b/src/image/SkImage_Codec.cpp
index 3d815ce7f437409156b94c009a26e733ca77a270..8377655e27f68a06e113b466db90f6f7d5e40267 100644
--- a/src/image/SkImage_Codec.cpp
+++ b/src/image/SkImage_Codec.cpp
@@ -21,6 +21,8 @@ public:
     virtual void onDraw(SkCanvas*, SkScalar, SkScalar, const SkPaint*) SK_OVERRIDE;
     virtual void onDrawRectToRect(SkCanvas*, const SkRect*, const SkRect&, const SkPaint*) SK_OVERRIDE;
 
+    virtual bool isOpaque() const SK_OVERRIDE;
+
 private:
     SkData*     fEncodedData;
     SkBitmap    fBitmap;
@@ -73,3 +75,12 @@ SkImage* SkImage::NewEncodedData(SkData* data) {
 
     return SkNEW_ARGS(SkImage_Codec, (data, bitmap.width(), bitmap.height()));
 }
+
+
+bool SkImage_Codec::isOpaque() const {
+    if (!fBitmap.pixelRef()) {
+        return SkImage::isOpaque();

[reed1, 2014/07/18 20:50:02]

This will return false, even if the bitmap is opaque.

The absence of a pixelref for this image can just mean that we haven't decoded
the image *yet*

[Rémi Piotaix, 2014/07/18 21:12:50]

Yep.
I made this method const so SkImageDecoder::DecodeMemory() can't be called like
in other methods of SkImage_Codec.

Should i remove the 'const' attribute (or make fBitmap mutable ?)

[scroggo, 2014/07/18 21:39:14]

It does seem to me that fBitmap is logically mutable.

Might there be a situation where a client wants to know the opacity, but does
not want to necessarily decode yet?

+    }
+
+    return fBitmap.isOpaque();
+}