Make SkImageFilter methods const.

src/effects/SkAlphaThresholdFilter.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkAlphaThresholdFilter.h"
 #include "SkBitmap.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 #include "SkRegion.h"
 
 class SK_API SkAlphaThresholdFilterImpl : public SkImageFilter {
 public:
     SkAlphaThresholdFilterImpl(const SkRegion& region, SkScalar innerThreshold, SkScalar outerThreshold);
 
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkAlphaThresholdFilterImpl)
 
 protected:
     explicit SkAlphaThresholdFilterImpl(SkReadBuffer& buffer);
     virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;
 
     virtual bool onFilterImage(Proxy*, const SkBitmap& src, const SkMatrix&,
-                               SkBitmap* result, SkIPoint* offset) SK_OVERRIDE;
+                               SkBitmap* result, SkIPoint* offset) const SK_OVERRIDE;
 #if SK_SUPPORT_GPU
     virtual bool asNewEffect(GrEffectRef** effect, GrTexture* texture,
                              const SkMatrix& matrix, const SkIRect& bounds) const SK_OVERRIDE;
 #endif
 
 private:
     SkRegion fRegion;
     SkScalar fInnerThreshold;
     SkScalar fOuterThreshold;
     typedef SkImageFilter INHERITED;
@@ skipping 262 matching lines @@
 
 void SkAlphaThresholdFilterImpl::flatten(SkWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);
     buffer.writeScalar(fInnerThreshold);
     buffer.writeScalar(fOuterThreshold);
     buffer.writeRegion(fRegion);
 }
 
 bool SkAlphaThresholdFilterImpl::onFilterImage(Proxy*, const SkBitmap& src,
                                                const SkMatrix& matrix, SkBitmap* dst,
-                                               SkIPoint* offset) {
+                                               SkIPoint* offset) const {
     SkASSERT(src.config() == SkBitmap::kARGB_8888_Config);
 
     if (src.config() != SkBitmap::kARGB_8888_Config) {
         return false;
     }
 
     SkMatrix localInverse;
     if (!matrix.invert(&localInverse)) {
         return false;
     }
@@ skipping 39 matching lines @@
                                                   (U8CPU)(SkColorGetG(source) * scale),
                                                   (U8CPU)(SkColorGetB(source) * scale));
                 }
             }
             dptr[y * dst->width() + x] = output_color;
         }
     }
 
     return true;
 }