add newImage API

include/core/SkImage.h

Index: include/core/SkImage.h
diff --git a/include/core/SkImage.h b/include/core/SkImage.h
index 6070b6bf6bfefdd50ba5bc07ca8e118f54ef9165..d4a468d592e13105c70f4364679be398b733cb04 100644
--- a/include/core/SkImage.h
+++ b/include/core/SkImage.h
@@ -124,6 +124,19 @@ public:
      */
     SkSurface* newSurface(const SkImageInfo&, const SkSurfaceProps* = NULL) const;
 
+    /**
+     *  Return an image that is a rescale of this image (using newWidth, newHeight).
+     *
+     *  If subset is NULL, then the entire original image is used as the src for the scaling.
+     *  If subset is not NULL, then it is intersected with the original src-bounds. If that
+     *  intersection is empty, NULL is returned, else the intersection is used as the src for
+     *  the scaling.
+     *
+     *  Note: it is legal for the returned image to be the same instance as the src image
+     *  (if the new dimensions == the src dimensions and any subset encloses the entire src).
+     */
+    SkImage* newImage(int newWidth, int newHeight, const SkIRect* subset = NULL) const;

[bsalomon, 2014/12/22 21:31:06]

Should there be control over filtering mode/quality? How does subset interact
with filtering?

Are the denominators in the scale factors computed before or after subset is
clipped to the src bounds? For example if the old image is 100 high, the
newHeight is 200, the subrect goes from -50, 50 in y - what is the height of the
returned image and does it have any padding/trans-black pixels?

[reed1, 2014/12/22 21:39:47]

Good question -- in my next rev. I'm proposing changing the API to require that
subset be exactly that : a subset of the original bounds. less is more.

+
 protected:
     SkImage(int width, int height) :
         fWidth(width),