Image filters: implement SkImage::makeWithFilter().

include/core/SkImage.h

Index: include/core/SkImage.h
diff --git a/include/core/SkImage.h b/include/core/SkImage.h
index 31985a6c6936a1b2918f7809d57a1c331a20841b..506721e41722f9b6333847cf2f46d271e60ab694 100644
--- a/include/core/SkImage.h
+++ b/include/core/SkImage.h
@@ -320,6 +320,25 @@ public:
      */
     sk_sp<SkImage> makeTextureImage(GrContext*) const;
 
+    /**
+     *  Apply a given image filter to this image, and return the filtered result.
+     *
+     *  The subset represents the active portion of this image. The return value is similarly an
+     *  Skimage, with an active subset (outSubset). This is usually used with texture-backed
+     *  images, where the texture may be approx-match and thus larger than the required size.
+     *
+     *  clipBounds represents the maximum size of the image which may be produced.
+     *
+     *  offset is the amount to translate the resulting image relative to the src when it is drawn.
+     *  This is an out-param.
+     *
+     *  If the result image cannot be created, or the result would be transparent black, null
+     *  is returned, in which case the offset and subset parameters should be ignored by the caller.
+     */
+    sk_sp<SkImage> makeWithFilter(const SkImageFilter* filter, const SkIRect& subset,
+                                  const SkIRect& clipBounds, SkIRect* outSubset,
+                                  SkIPoint* offset);

[reed1, 2016/05/19 16:33:34]

method should be const

[Stephen White, 2016/05/19 17:20:06]

I tried that, but SkSpecialImage wants to take a ref on "this", so sk_ref_sp
complained about the constness. I see SkImage::makeSubset() does a
const_cast<SkImage*>. So I'll do that too.

(Kind of feels like sk_ref_sp could take a const T*, given that ref() is const
and the refcount is mutable.)

+
     /** Drawing params for which a deferred texture image data should be optimized. */
     struct DeferredTextureImageUsageParams {
         SkMatrix        fMatrix;