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
 
+#include "SkFilterQuality.h"
 #include "SkImageInfo.h"
 #include "SkImageEncoder.h"
 #include "SkRefCnt.h"
 #include "SkScalar.h"
 #include "SkShader.h"
 
 class SkData;
 class SkCanvas;
 class SkImageGenerator;
 class SkPaint;
@@ skipping 104 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;
 
     const char* toString(SkString*) 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 specifies subset of src-pixels used for scaling. If
+     *  subset extends beyond the bounds of the original image, then NULL is returned.
+     *
+     *  Notes:
+     *  - it is legal for the returned image to be the same instance as the src image
+     *    (if the new dimensions == the src dimensions and subset is NULL or == src dimensions).
+     *
+     *  - it is legal for the "scaled" image to have changed its SkAlphaType from unpremul
+     *    to premul (as required by the impl). The image should draw (nearly) identically,

[scroggo, 2015/01/21 22:24:57]

As discussed in person, it seems like this will *require* changing to premul
(unless we break down and let SkImage know its SkImageInfo, or at least its
SkAlphaType).

+     *    since during drawing we will "apply the alpha" to the pixels. Future optimizations
+     *    may take away this caveat, preserving unpremul.
+     */
+    SkImage* newImage(int newWidth, int newHeight, const SkIRect* subset = NULL,
+                      SkFilterQuality = kNone_SkFilterQuality) const;
+
 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