add GM to test imagefilters + xfermodes

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) {
+        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.setImageFilter(imf);
+        paint.setXfermodeMode(mode);
+        canvas->drawOval(r1, paint);
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        // 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);
+            this->doDraw(canvas, modes[i], imf);
+            canvas->restore();
+            
+            canvas->translate(0, 250);
+        }
+    }
+
+private:
+    typedef GM INHERITED;
+};
+DEF_GM( return new ImageFilterXfermodeTestGM; )
+