Fix SkXfermodeImageFilter GPU fast path for differing sizes.

gm/xfermodeimagefilter.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 "gm.h"
 #include "sk_tool_utils.h"
 #include "SkArithmeticMode.h"
 #include "SkImage.h"
 #include "SkImageSource.h"
 #include "SkOffsetImageFilter.h"
 #include "SkXfermodeImageFilter.h"
 
 #define WIDTH 600
-#define HEIGHT 600
+#define HEIGHT 700
 #define MARGIN 12
 
 namespace skiagm {
 
 class XfermodeImageFilterGM : public GM {
 public:
     XfermodeImageFilterGM(){
         this->setBGColor(0xFF000000);
     }
 
@@ skipping 134 matching lines @@
             filter.reset(SkXfermodeImageFilter::Create(
                                     mode, offsetBackground, offsetForeground, &rect));
             paint.setImageFilter(filter);
             DrawClippedPaint(canvas, clipRect, paint, x, y);
             x += fBitmap.width() + MARGIN;
             if (x + fBitmap.width() > WIDTH) {
                 x = 0;
                 y += fBitmap.height() + MARGIN;
             }
         }
+        // Test small bg, large fg with Screen (uses shader blend)
+        mode.reset(SkXfermode::Create(SkXfermode::kScreen_Mode));
+        SkImageFilter::CropRect cropRect(SkRect::MakeXYWH(10, 10, 60, 60));
+        SkAutoTUnref<SkImageFilter> cropped(
+            SkOffsetImageFilter::Create(0, 0, foreground, &cropRect));
+        filter.reset(SkXfermodeImageFilter::Create(mode, cropped, background));
+        paint.setImageFilter(filter);
+        DrawClippedPaint(canvas, clipRect, paint, x, y);
+        x += fBitmap.width() + MARGIN;
+        if (x + fBitmap.width() > WIDTH) {
+            x = 0;
+            y += fBitmap.height() + MARGIN;
+        }
+        // Test small fg, large bg with Screen (uses shader blend)
+        filter.reset(SkXfermodeImageFilter::Create(mode, background, cropped));
+        paint.setImageFilter(filter);
+        DrawClippedPaint(canvas, clipRect, paint, x, y);
+        x += fBitmap.width() + MARGIN;
+        if (x + fBitmap.width() > WIDTH) {
+            x = 0;
+            y += fBitmap.height() + MARGIN;
+        }
     }
 
 private:
     static void DrawClippedBitmap(SkCanvas* canvas, const SkBitmap& bitmap, const SkPaint& paint,
                            int x, int y) {
         canvas->save();
         canvas->translate(SkIntToScalar(x), SkIntToScalar(y));
         canvas->clipRect(SkRect::MakeWH(
             SkIntToScalar(bitmap.width()), SkIntToScalar(bitmap.height())));
         canvas->drawBitmap(bitmap, 0, 0, &paint);
@@ skipping 13 matching lines @@
     SkAutoTUnref<SkImage> fCheckerboard;
 
     typedef GM INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 DEF_GM( return new XfermodeImageFilterGM; );
 
 }