add SkLerpXfermode

gm/lerpmode.cpp

Index: gm/lerpmode.cpp
diff --git a/gm/lerpmode.cpp b/gm/lerpmode.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..481af359b264b07f2034880df5f9613eab8ed577
--- /dev/null
+++ b/gm/lerpmode.cpp
@@ -0,0 +1,64 @@
+/*
+ * 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 "SkCanvas.h"
+#include "SkLerpXfermode.h"
+
+static void show_circlelayers(SkCanvas* canvas, SkXfermode* mode) {
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    SkRect r, bounds = { 10, 10, 110, 110 };
+
+    r = bounds;
+    r.fRight = bounds.centerX();
+    canvas->drawRect(r, paint);
+
+    canvas->saveLayer(&bounds, NULL);
+    
+    paint.setColor(0x80FF0000);
+    r = bounds;
+    r.inset(20, 0);
+    canvas->drawOval(r, paint);
+    
+    paint.setColor(0x800000FF);
+    r = bounds;
+    r.inset(0, 20);
+    paint.setXfermode(mode);
+    canvas->drawOval(r, paint);
+    
+    canvas->restore();
+}
+
+class LerpXfermodeGM : public skiagm::GM {
+public:
+    LerpXfermodeGM() {}
+
+protected:
+    virtual SkString onShortName() SK_OVERRIDE {
+        return SkString("lerpmode");
+    }
+
+    virtual SkISize onISize() SK_OVERRIDE {
+        return SkISize::Make(240, 120);
+    }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        show_circlelayers(canvas, NULL);
+        canvas->translate(150, 0);
+        SkAutoTUnref<SkXfermode> mode(SkLerpXfermode::Create(0.5f));
+        show_circlelayers(canvas, mode.get());
+    }
+
+private:
+    typedef skiagm::GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+DEF_GM( return SkNEW(LerpXfermodeGM); )
+