add newImage API

include/core/SkImage.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImage_DEFINED
 #define SkImage_DEFINED
 
@@ skipping 106 matching lines @@
 
     /**
      *  Return a new surface that is compatible with this image's internal representation
      *  (e.g. raster or gpu).
      *
      *  If no surfaceprops are specified, the image will attempt to match the props of when it
      *  was created (if it came from a surface).
      */
     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),
         fHeight(height),
         fUniqueID(NextUniqueID()) {
 
         SkASSERT(width >= 0);
         SkASSERT(height >= 0);
     }
 
@@ skipping 14 matching lines @@
      *  Draw the image, cropped to the src rect, to the dst rect of a canvas.
      *  If src is larger than the bounds of the image, the rest of the image is
      *  filled with transparent black pixels.
      *
      *  See SkCanvas::drawBitmapRectToRect for similar behavior.
      */
     void drawRect(SkCanvas*, const SkRect* src, const SkRect& dst, const SkPaint*) const;
 };
 
 #endif