Make readpixels work on GrTextures

src/gpu/GrSurfacePriv.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrSurfacePriv_DEFINED
 #define GrSurfacePriv_DEFINED
 
 #include "GrSurface.h"
 
 /** Class that adds methods to GrSurface that are only intended for use internal to Skia.
     This class is purely a privileged window into GrSurface. It should never have additional data
     members or virtual methods.
     Non-static methods that are not trivial inlines should be spring-boarded (e.g. declared and
     implemented privately in GrSurface with a inline public method here). */
 class GrSurfacePriv {
 public:
+    /** Helpers used in read/write pixels implementations. The paramters are adjusted so that the
+        read/write respects the bounds of a surface. If the input *rowBytes is 0 it will be
+        the tight row bytes (based on width and bpp) on output. */
+    static bool AdjustReadPixelParams(int surfaceWidth,
+                                      int surfaceHeight,
+                                      size_t bpp,
+                                      int* left, int* top, int* width, int* height,
+                                      void** data,
+                                      size_t* rowBytes);
+    static bool AdjustWritePixelParams(int surfaceWidth,
+                                      int surfaceHeight,
+                                      size_t bpp,
+                                      int* left, int* top, int* width, int* height,
+                                      const void** data,
+                                      size_t* rowBytes);
     /**
      * Derive a SkImageInfo from the surface's descriptor. The caller must provide the alpha type as
      * GrSurface has no equivalent.
      */
     SkImageInfo info(SkAlphaType alphaType) const { return fSurface->info(alphaType); }
 
     /**
      * Write the contents of the surface to a PNG. Returns true if successful.
      * @param filename      Full path to desired file
      */
@@ skipping 17 matching lines @@
     friend class GrSurface; // to construct/copy this type.
 };
 
 inline GrSurfacePriv GrSurface::surfacePriv() { return GrSurfacePriv(this); }
 
 inline const GrSurfacePriv GrSurface::surfacePriv() const {
     return GrSurfacePriv(const_cast<GrSurface*>(this));
 }
 
 #endif