Add an option to create unpremultiplied bitmaps.

include/core/SkBitmap.h

Index: include/core/SkBitmap.h
diff --git a/include/core/SkBitmap.h b/include/core/SkBitmap.h
index ad185479801c8b71d66c7e7381412a3be5ab13e8..9b5897d5eb60ba03e52646cea1388a3ba062c2dc 100644
--- a/include/core/SkBitmap.h
+++ b/include/core/SkBitmap.h
@@ -104,6 +104,12 @@ public:
     /** DEPRECATED, use config()
     */
     Config  getConfig() const { return this->config(); }
+
+    /** Whether the colors are stored premultiplied. If the bitmap is opaque,
+        the return value is undefined.
+    */
+    bool premultiplied() const { return 0 == (fFlags & kColorsAreNotPremultiplied_Flag); }

[reed1, 2013/06/12 20:20:00]

isPremultiplied() ?
isUnpremultiplied() ?

+
     /** Return the bitmap's width, in pixels.
     */
     int width() const { return fWidth; }
@@ -250,8 +256,14 @@ public:
     /** Set the bitmap's config and dimensions. If rowBytes is 0, then
         ComputeRowBytes() is called to compute the optimal value. This resets
         any pixel/colortable ownership, just like reset().
-    */
-    void setConfig(Config, int width, int height, size_t rowBytes = 0);
+        @param premul Whether the color values are premultiplied. A value of
+            false will only be respected if Config supports unpremultiplied
+            colors, which is currently only true for kARGB_8888.
+            A bitmap with unpremultiplied pixels cannot be drawn to or from
+            by Skia, but may be used by other libraries.
+    */
+    void setConfig(Config, int width, int height, size_t rowBytes = 0,
+                   bool premul = true);

[djsollen, 2013/06/12 17:59:21]

why not just add a new config for unpremultiplied 8888?

[scroggo, 2013/06/12 18:24:42]

That was my first approach, but it was brought up that ultimately we may want
independent choices, more like SkImage. Adding this new config would tie
unpremultiplied to the native color ordering and 8888.

Maybe that's okay though? 

     /** Use this to assign a new pixel address for an existing bitmap. This
         will automatically release any pixelref previously installed. Only call
         this if you are handling ownership/lifetime of the pixel memory.
@@ -364,7 +376,7 @@ public:
         return this->getPixels() != NULL &&
                ((this->config() != kIndex8_Config &&
                  this->config() != kRLE_Index8_Config) ||
-                       fColorTable != NULL);
+                       fColorTable != NULL) && this->premultiplied();
     }
 
     /** Returns the pixelRef's texture, or NULL
@@ -656,16 +668,17 @@ private:
     mutable SkColorTable* fColorTable;    // only meaningful for kIndex8
 
     enum Flags {
-        kImageIsOpaque_Flag     = 0x01,
-        kImageIsVolatile_Flag   = 0x02,
-        kImageIsImmutable_Flag  = 0x04,
+        kImageIsOpaque_Flag             = 0x01,
+        kImageIsVolatile_Flag           = 0x02,
+        kImageIsImmutable_Flag          = 0x04,
 #ifdef SK_BUILD_FOR_ANDROID
         /* A hint for the renderer responsible for drawing this bitmap
          * indicating that it should attempt to use mipmaps when this bitmap
          * is drawn scaled down.
          */
-        kHasHardwareMipMap_Flag = 0x08,
+        kHasHardwareMipMap_Flag         = 0x08,
 #endif
+        kColorsAreNotPremultiplied_Flag = 0x10,
     };
 
     uint32_t    fRowBytes;