CG imagedecoder never sets isOpaque, so add method to SkBitmap to compute that,

and call it from CG imagedecoder.
Review URL: https://codereview.appspot.com/6816101

git-svn-id: http://skia.googlecode.com/svn/trunk@6334 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 18 insertions, 0 deletions

diff --git a/include/core/SkBitmap.h b/include/core/SkBitmap.h
index 9c81e836f2..ef4cdd9c9a 100644
--- a/include/core/SkBitmap.h
+++ b/include/core/SkBitmap.h
@@ -223,6 +223,24 @@ public:
     static size_t ComputeSize(Config, int width, int height);
 
     /**
+     *  This will brute-force return true if all of the pixels in the bitmap
+     *  are opaque. If it fails to read the pixels, or encounters an error,
+     *  it will return false.
+     *
+     *  Since this can be an expensive operation, the bitmap stores a flag for
+     *  this (isOpaque, setIsOpaque). Only call this if you need to compute this
+     *  value from "unknown" pixels.
+     */
+    static bool ComputeIsOpaque(const SkBitmap&);
+
+    /**
+     *  Calls ComputeIsOpaque, and passes its result to setIsOpaque().
+     */
+    void computeAndSetOpaquePredicate() {
+        this->setIsOpaque(ComputeIsOpaque(*this));
+    }
+
+    /**
      *  Return the bitmap's bounds [0, 0, width, height] as an SkRect
      */
     void getBounds(SkRect* bounds) const;