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 495 matching lines @@
   // 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,
                                  ContextProvider* offscreen_contexts,
+                                 gfx::Point origin,
                                  SkImageFilter* filter,
                                  ScopedResource* source_texture_resource) {
   if (!filter)
     return SkBitmap();
 
   if (!offscreen_contexts || !offscreen_contexts->GrContext())
     return SkBitmap();
 
   ResourceProvider::ScopedWriteLockGL lock(renderer->resource_provider(),
                                            source_texture_resource->id());
@@ skipping 44 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(SkIntToScalar(-origin.x()), SkIntToScalar(-origin.y()));

[danakj, 2013/08/29 02:07:16]

Can you add a TODO here stating that the filter should be scaled by the scale
from the layer space of the root-most layer drawn into the render pass draw
quad's texture (ie. the surface owning texture), to the render pass draw quad's
texture? And point to a crbug where we will do this?

[Stephen White, 2013/08/29 17:07:00]

Done.

   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 181 matching lines @@
       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,
                                        frame->offscreen_context_provider,
+                                       quad->rect.origin(),
                                        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(
@@ skipping 2362 matching lines @@
   std::string unique_context_name = base::StringPrintf(
       "%s-Offscreen-%p",
       Settings().compositor_name.c_str(),
       context_);
   offscreen_context_provider->Context3d()->pushGroupMarkerEXT(
       unique_context_name.c_str());
 }
 
 
 }  // namespace cc