Add Xfermode bench. Also clear before rendering in bench (rather than after).

bench/XfermodeBench.cpp

Index: bench/XfermodeBench.cpp
===================================================================
--- bench/XfermodeBench.cpp	(revision 0)
+++ bench/XfermodeBench.cpp	(revision 0)
@@ -0,0 +1,70 @@
+
+/*
+ * 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 "SkBenchmark.h"
+#include "SkCanvas.h"
+#include "SkPaint.h"
+#include "SkRandom.h"
+#include "SkString.h"
+#include "SkXfermode.h"
+
+// Benchmark that draws non-AA rects with an SkXfermode::Mode
+class XfermodeBench : public SkBenchmark {
+public:
+    XfermodeBench(void* param, SkXfermode::Mode mode) : SkBenchmark(param) {
+        fXfermode.reset(SkXfermode::Create(mode));
+        SkASSERT(NULL != fXfermode.get() || SkXfermode::kSrcOver_Mode == mode);
+        fName.printf("Xfermode_%s", SkXfermode::ModeName(mode));
+    }
+
+protected:
+    virtual const char* onGetName() SK_OVERRIDE { return fName.c_str(); }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        SkISize size = canvas->getDeviceSize();
+        SkMWCRandom random;
+        for (int i = 0; i < kNumRects; ++i) {
+            SkPaint paint;
+            paint.setXfermode(fXfermode.get());
+            paint.setColor(random.nextU());
+            SkScalar w = random.nextRangeScalar(SkIntToScalar(kMinSize), SkIntToScalar(kMaxSize));
+            SkScalar h = random.nextRangeScalar(SkIntToScalar(kMinSize), SkIntToScalar(kMaxSize));
+            SkRect rect = SkRect::MakeXYWH(
+                random.nextUScalar1() * (size.fWidth - w),
+                random.nextUScalar1() * (size.fHeight - h),
+                w,
+                h
+            );
+            canvas->drawRect(rect, paint);
+        }
+    }
+
+private:
+    enum {
+        kNumRects = SkBENCHLOOP(1000),
+        kMinSize = 10,
+        kMaxSize = 400,
+    };
+    SkAutoTUnref<SkXfermode> fXfermode;
+    SkString fName;
+    
+    typedef SkBenchmark INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+

[robertphillips, 2013/03/31 16:44:13]

What about just adding a bench for each xfermode (i.e., why stop at 3)?

+// These modes were chosen because they are expected to be successively harder for the GPU.
+// kSrc can disable blending, kSrcOver cannot, kDarken requires reading the dst pixel in the shader.
+static SkBenchmark* Fact0(void* p) { return new XfermodeBench(p, SkXfermode::kSrc_Mode); }
+static SkBenchmark* Fact1(void* p) { return new XfermodeBench(p, SkXfermode::kSrcOver_Mode); }
+static SkBenchmark* Fact2(void* p) { return new XfermodeBench(p, SkXfermode::kDarken_Mode); }
+
+static BenchRegistry gReg0(Fact0);
+static BenchRegistry gReg1(Fact1);
+static BenchRegistry gReg2(Fact2);