Add GM for SkPixelXorXfermode

gm/pixelxorxfermode.cpp

+/*
+ * Copyright 2016 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 "Resources.h"
+
+#include "SkImageDecoder.h"
+#include "SkPixelXorXfermode.h"
+#include "SkStream.h"
+
+class PixelXorXfermodeGM : public skiagm::GM {
+public:
+    PixelXorXfermodeGM() { }
+
+protected:
+    SkString onShortName() override {
+        return SkString("pixelxorxfermode");
+    }
+
+    SkISize onISize() override { return SkISize::Make(512, 512); }
+
+    void onOnceBeforeDraw() override {
+        SkImageDecoder* codec = nullptr;
+        SkString resourcePath = GetResourcePath("mandrill_512.png");
+        SkFILEStream stream(resourcePath.c_str());
+        if (stream.isValid()) {
+            codec = SkImageDecoder::Factory(&stream);
+        }
+        if (codec) {
+            stream.rewind();
+            codec->decode(&stream, &fBM, kN32_SkColorType, SkImageDecoder::kDecodePixels_Mode);
+            delete codec;
+        } else {
+            fBM.allocN32Pixels(1, 1);
+            fBM.eraseARGB(255, 255, 0 , 0); // red == bad
+        }
+    }
+
+    void onDraw(SkCanvas* canvas) override {
+        canvas->drawBitmap(fBM, 0, 0);
+
+        SkRect r = SkRect::MakeIWH(256, 256);
+
+        // Negate the red channel of the dst (via the ancillary color) but leave
+        // the green & blue channels alone
+        SkPaint p1;
+        p1.setColor(SK_ColorBLACK); // noop
+        p1.setXfermode(SkPixelXorXfermode::Create(SK_ColorRED));
+
+        canvas->drawRect(r, p1);
+
+        r.offsetTo(256.0f, 0.0f);
+
+        // Negate the dst color via the src color
+        SkPaint p2;
+        p2.setColor(SK_ColorWHITE);
+        p2.setXfermode(SkPixelXorXfermode::Create(SK_ColorBLACK)); // noop
+
+        canvas->drawRect(r, p2);
+
+        r.offsetTo(0.0f, 256.0f);
+
+        // Just return the original color
+        SkPaint p3;
+        p3.setColor(SK_ColorBLACK); // noop
+        p3.setXfermode(SkPixelXorXfermode::Create(SK_ColorBLACK)); // noop
+
+        canvas->drawRect(r, p3);
+
+        r.offsetTo(256.0f, 256.0f);
+
+        // Negate the red & green channels (via the ancillary color) but leave
+        // the blue channel alone
+        SkPaint p4;
+        p4.setColor(SK_ColorBLACK); // noop
+        p4.setXfermode(SkPixelXorXfermode::Create(SK_ColorYELLOW));
+
+        canvas->drawRect(r, p4);
+    }
+
+private:
+    SkBitmap fBM;
+
+    typedef GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+DEF_GM(return new PixelXorXfermodeGM;)