adjust GM to have a final opaque bg, to make it easier to triage

gm/imagefilters.cpp

 /*
  * Copyright 2015 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 "SkImageFilter.h"
 #include "SkColorMatrixFilter.h"
 
 /**
  *  Test drawing a primitive w/ an imagefilter (in this case, just matrix w/ identity) to see
  *  that we apply the xfermode *after* the image has been created and filtered, and not during
  *  the creation step (i.e. before it is filtered).
  *
  *  see skbug.com/3741
  */
 class ImageFilterXfermodeTestGM : public skiagm::GM {
 protected:
     SkString onShortName() override {
         return SkString("imagefilters_xfermodes");
     }
 
     SkISize onISize() override { return SkISize::Make(480, 480); }
 
     void doDraw(SkCanvas* canvas, SkXfermode::Mode mode, SkImageFilter* imf) {
+        SkAutoCanvasRestore acr(canvas, true);
+        canvas->clipRect(SkRect::MakeWH(220, 220));
+        
+        // want to force a layer, so modes like DstIn can combine meaningfully, but the final
+        // image can still be shown against our default (opaque) background. non-opaque GMs
+        // are a lot more trouble to compare/triage.
+        canvas->saveLayer(NULL, NULL);
+        canvas->drawColor(SK_ColorGREEN);
+
         SkPaint paint;
         paint.setAntiAlias(true);
         
         SkRect r0 = SkRect::MakeXYWH(10, 60, 200, 100);
         SkRect r1 = SkRect::MakeXYWH(60, 10, 100, 200);
         
         paint.setColor(SK_ColorRED);
         canvas->drawOval(r0, paint);
 
-        paint.setColor(0x800000FF);
+        paint.setColor(0x660000FF);
         paint.setImageFilter(imf);
         paint.setXfermodeMode(mode);
         canvas->drawOval(r1, paint);
     }
 
     void onDraw(SkCanvas* canvas) override {
+        canvas->translate(10, 10);
+
         // just need an imagefilter to trigger the code-path (which creates a tmp layer)
         SkAutoTUnref<SkImageFilter> imf(SkImageFilter::CreateMatrixFilter(SkMatrix::I(),
                                                                           kNone_SkFilterQuality));
 
         const SkXfermode::Mode modes[] = {
             SkXfermode::kSrcATop_Mode, SkXfermode::kDstIn_Mode
         };
         
         for (size_t i = 0; i < SK_ARRAY_COUNT(modes); ++i) {
             canvas->save();
             this->doDraw(canvas, modes[i], NULL);
-            canvas->translate(250, 0);
+            canvas->translate(240, 0);
             this->doDraw(canvas, modes[i], imf);
             canvas->restore();
             
-            canvas->translate(0, 250);
+            canvas->translate(0, 240);
         }
     }
 
 private:
     typedef GM INHERITED;
 };
 DEF_GM( return new ImageFilterXfermodeTestGM; )