detect when we can filter bitmaps/images directly, w/o a tmp layer

include/core/SkDevice.h

Index: include/core/SkDevice.h
diff --git a/include/core/SkDevice.h b/include/core/SkDevice.h
index c52c579424a2ad7e450b501585052d0aa8eea050..fd8bb5752ff52b6a02232b3b623d0a577dfbbda9 100644
--- a/include/core/SkDevice.h
+++ b/include/core/SkDevice.h
@@ -374,9 +374,27 @@ private:
     friend class SkDeviceFilteredPaint;
     friend class SkImageFilter::DeviceProxy;
     friend class SkNoPixelsBitmapDevice;
-
     friend class SkSurface_Raster;
 
+    /**
+     *  Returns true if the caller can call the imagefilter "directly" on the src bitmap,
+     *  without needing to first draw it into a temp layer.
+     *
+     *  The conditions are:
+     *  - the paint has an imagefilter
+     *  - the matrix is only translate (or identity)
+     *  - the device itself does not want to handle the filter

[Stephen White, 2015/12/02 23:45:15]

So this will only work for the raster path, then? I think all the GPU filters
are handled by SkGpuDevice.

[reed1, 2015/12/03 21:26:51]

Fixed.

+     *
+     *  If all of the above are true, the caller may call filterSprite()
+     */
+    bool canCallFilterSprite(const SkMatrix*, const SkPaint&);
+
+    /**
+     *  Will invoke the paint's imagefilter directly on the bitmap, and draw the result.
+     *  Assumes that the caller has previously called canCallFilterSprite().
+     */
+    void filterSprite(const SkDraw&, const SkBitmap&, int x, int y, const SkPaint&);
+
     // used to change the backend's pixels (and possibly config/rowbytes)
     // but cannot change the width/height, so there should be no change to
     // any clip information.