Add benchmark for PremultiplyAlpha and UnpremultiplyAlpha in Skia

bench/PremulAndUnpremulAlphaOpsBench.cpp

Index: bench/PremulAndUnpremulAlphaOpsBench.cpp
diff --git a/bench/PremulAndUnpremulAlphaOpsBench.cpp b/bench/PremulAndUnpremulAlphaOpsBench.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..a29bf7b4b6134b5317b168d3bda2325c3448599b
--- /dev/null
+++ b/bench/PremulAndUnpremulAlphaOpsBench.cpp
@@ -0,0 +1,74 @@
+
+/*
+ * 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 "SkConfig8888.h"
+
+class PremulAndUnpremulAlphaOpsBench : public SkBenchmark {
+public:
+    PremulAndUnpremulAlphaOpsBench(void* param, SkCanvas::Config8888 config,
+                                   const char* name)
+        : INHERITED(param) {
+        unPremulConfig = config;
+        benchName = name;
+    }
+
+protected:
+    virtual const char* onGetName() SK_OVERRIDE {
+        return benchName;
+    }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        canvas->clear(SK_ColorBLACK);
+        SkISize size = canvas->getDeviceSize();
+
+        SkBitmap bmp1;
+        bmp1.setConfig(SkBitmap::kARGB_8888_Config, size.width(),
+                       size.height());
+        bmp1.allocPixels();
+        SkAutoLockPixels alp(bmp1);
+        uint32_t* pixels = reinterpret_cast<uint32_t*>(bmp1.getPixels());
+        for (int h = 0; h < size.height(); ++h) {
+            for (int w = 0; w < size.width(); ++w)
+                pixels[h * size.width() + w] = SkPackConfig8888(unPremulConfig,
+                    h & 0xFF, w & 0xFF, w & 0xFF, w & 0xFF);
+        }
+
+        SkBitmap bmp2;
+        bmp2.setConfig(SkBitmap::kARGB_8888_Config, size.width(),
+                       size.height());
+
+        static const int kLoopCount = SkBENCHLOOP(10);
+        for (int loop = 0; loop < kLoopCount; ++loop) {
+            // Unpremul -> Premul
+            canvas->writePixels(bmp1, 0, 0, unPremulConfig);
+            // Premul -> Unpremul
+            canvas->readPixels(&bmp2, 0, 0, unPremulConfig);
+        }
+    }
+
+private:
+    SkCanvas::Config8888 unPremulConfig;
+    const char* benchName;

[tomhudson, 2013/06/12 09:23:34]

I wasn't reading carefully enough earlier - another nit from the Skia style
guide is that member variables should all start with 'f', so these should be
fUnPremulConfig and fBenchName.

It's more in keeping with the SkBenchmark idiom to
 - have a SkString fName;
 - dynamically assemble the name in the constructor.

You shouldn't need to be passing the name in to the constructor; your
constructor knows everything it needs to create the name. SkAAClipBench is a
good a simple example. We prefer this style for change-proofing (along the lines
of Don't Repeat Yourself).

onGetName() would then return fName.c_str()

[Jun Jiang, 2013/06/12 16:59:26]

Done.

+    typedef SkBenchmark INHERITED;
+};
+
+static SkBenchmark* fact0(void* p) {
+    return new PremulAndUnpremulAlphaOpsBench(p,
+        SkCanvas::kRGBA_Unpremul_Config8888,
+        "premul_and_unpremul_alpha_RGBA8888");
+}
+static SkBenchmark* fact1(void* p) {
+    return new PremulAndUnpremulAlphaOpsBench(p,
+        SkCanvas::kNative_Unpremul_Config8888,
+        "premul_and_unpremul_alpha_Native8888");
+}
+
+static BenchRegistry gReg0(fact0);
+static BenchRegistry gReg1(fact1);