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

include/core/SkDevice.h

 /*
  * Copyright 2010 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkDevice_DEFINED
 #define SkDevice_DEFINED
 
@@ skipping 356 matching lines @@
     }
 
 private:
     friend class SkCanvas;
     friend struct DeviceCM; //for setMatrixClip
     friend class SkDraw;
     friend class SkDrawIter;
     friend class SkDeviceFilteredPaint;
     friend class SkImageFilter::DeviceProxy;
     friend class SkNoPixelsBitmapDevice;
+    friend class SkSurface_Raster;
 
-    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.
     // TODO: move to SkBitmapDevice
     virtual void replaceBitmapBackendForRasterSurface(const SkBitmap&) {}
 
     virtual bool forceConservativeRasterClip() const { return false; }
 
     // just called by SkCanvas when built as a layer
@@ skipping 10 matching lines @@
     SkSurfaceProps fSurfaceProps;
 
 #ifdef SK_DEBUG
     bool        fAttachedToCanvas;
 #endif
 
     typedef SkRefCnt INHERITED;
 };
 
 #endif