Pass the quad's rect (contents_rect) origin to skia image filters as an offset in the CTM.

cc/output/gl_renderer.cc

 // Copyright 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/output/gl_renderer.h"
 
 #include <algorithm>
 #include <limits>
 #include <set>
 #include <string>
@@ skipping 497 matching lines @@
   // Flush the GL context so rendering results from this context are
   // visible in the compositor's context.
   offscreen_contexts->Context3d()->flush();
 
   // Use the compositor's GL context again.
   renderer->Context()->makeContextCurrent();
   return source;
 }
 
 static SkBitmap ApplyImageFilter(GLRenderer* renderer,
+                                 gfx::Rect rect,

[danakj, 2013/08/19 21:09:08]

better variable name than the type of the variable, what this input represents
to this function?

why pass in a rect but only use the origin? how about passing in just the rect's
OffsetFromOrigin()?

                                  SkImageFilter* filter,
                                  ScopedResource* source_texture_resource) {
   if (!filter)
     return SkBitmap();
 
   ContextProvider* offscreen_contexts =
       renderer->resource_provider()->offscreen_context_provider();
   if (!offscreen_contexts || !offscreen_contexts->GrContext())
     return SkBitmap();
 
@@ skipping 46 matching lines @@
       skia::AdoptRef(scratch_texture.detach());
 
   // Create a device and canvas using that backing store.
   SkGpuDevice device(offscreen_contexts->GrContext(), backing_store.get());
   SkCanvas canvas(&device);
 
   // Draw the source bitmap through the filter to the canvas.
   SkPaint paint;
   paint.setImageFilter(filter);
   canvas.clear(SK_ColorTRANSPARENT);
+  canvas.translate(SkFloatToScalar(rect.x()), SkFloatToScalar(rect.y()));
   canvas.drawSprite(source, 0, 0, &paint);
 
   // Flush skia context so that all the rendered stuff appears on the
   // texture.
   offscreen_contexts->GrContext()->flush();
 
   // Flush the GL context so rendering results from this context are
   // visible in the compositor's context.
   offscreen_contexts->Context3d()->flush();
 
@@ skipping 176 matching lines @@
       SkColorFilter* colorfilter_rawptr = NULL;
       quad->filter->asColorFilter(&colorfilter_rawptr);
       cf = skia::AdoptRef(colorfilter_rawptr);
     }
 
     if (cf && cf->asColorMatrix(color_matrix) && !quad->filter->getInput(0)) {
       // We have a single color matrix as a filter; apply it locally
       // in the compositor.
       use_color_matrix = true;
     } else {
-      filter_bitmap =
-          ApplyImageFilter(this, quad->filter.get(), contents_texture);
+      filter_bitmap = ApplyImageFilter(
+          this, quad->rect, quad->filter.get(), contents_texture);
     }
   } else if (!quad->filters.IsEmpty()) {
     FilterOperations optimized_filters =
         RenderSurfaceFilters::Optimize(quad->filters);
 
     if ((optimized_filters.size() == 1) &&
         (optimized_filters.at(0).type() == FilterOperation::COLOR_MATRIX)) {
       memcpy(
           color_matrix, optimized_filters.at(0).matrix(), sizeof(color_matrix));
       use_color_matrix = true;
@@ skipping 2364 matching lines @@
   std::string unique_context_name = base::StringPrintf(
       "%s-Offscreen-%p",
       Settings().compositor_name.c_str(),
       context_);
   resource_provider()->offscreen_context_provider()->Context3d()->
     pushGroupMarkerEXT(unique_context_name.c_str());
 }
 
 
 }  // namespace cc