Improve the performance of SkConvertConfig8888Pixels using Array lookup

bench/PremulAndUnpremulAlphaOpsBench.cpp

Index: bench/PremulAndUnpremulAlphaOpsBench.cpp
diff --git a/bench/PremulAndUnpremulAlphaOpsBench.cpp b/bench/PremulAndUnpremulAlphaOpsBench.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..43a62649bbaa059418656d630bdd7e17620b1929
--- /dev/null
+++ b/bench/PremulAndUnpremulAlphaOpsBench.cpp
@@ -0,0 +1,61 @@
+
+/*
+ * 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();
+
+        static const int kLoopCount = SkBENCHLOOP(10);
+        for (int loop = 0; loop < kLoopCount; ++loop) {
+            SkBitmap bmp1;
+            bmp1.setConfig(SkBitmap::kARGB_8888_Config, size.width(), size.height());
+            bmp1.allocPixels();

[bsalomon, 2013/06/10 13:48:22]

Can't all this setup of bmp1 be done outside the loop? Maybe it could even
outside the timer entirely by having a member bitmap var and overriding
onPreDraw() (and then freeing up the pixels in onPostDraw()).

[Jun Jiang, 2013/06/11 14:46:20]

Yes, the setup of bmp1 can be done outside of the loop. As for moving it into
onPredraw(), there may be a issue that it can not get the size of the underlying
SkCanvas.

+            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);
+            }
+            // Unpremul -> Premul
+            canvas->writePixels(bmp1, 0, 0, unPremulConfig);
+
+            SkBitmap bmp2;
+            bmp2.setConfig(SkBitmap::kARGB_8888_Config, size.width(), size.height());
+            // Premul -> Unpremul
+            canvas->readPixels(&bmp2, 0, 0, unPremulConfig);
+        }
+    }
+
+private:
+    SkCanvas::Config8888 unPremulConfig;
+    const char* benchName;
+    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);