Adding new benchmark to test image decoding performance.

bench/DecodingSubsetBench.cpp

Index: bench/DecodingSubsetBench.cpp
diff --git a/bench/DecodingSubsetBench.cpp b/bench/DecodingSubsetBench.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..dc3c9f39cc5dbc7d2b14644a3b0a88dc5cbde00f
--- /dev/null
+++ b/bench/DecodingSubsetBench.cpp
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+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "DecodingSubsetBench.h"
+#include "SkData.h"
+#include "SkImageDecoder.h"
+#include "SkOSFile.h"
+#include "SkStream.h"
+
+/*
+ *
+ * This benchmark is designed to test the performance of image subset decoding.
+ * It is invoked from the nanobench.cpp file.
+ *
+ */
+DecodingSubsetBench::DecodingSubsetBench(SkString path, SkColorType colorType,
+        const int divisor)
+    : fColorType(colorType)
+    , fDivisor(divisor)
+{
+    // Parse filename and the color type to give the benchmark a useful name
+    SkString baseName = SkOSPath::Basename(path.c_str());
+    const char* colorName;
+    switch(colorType) {
+        case kN32_SkColorType:
+            colorName = "N32";
+            break;
+        case kRGB_565_SkColorType:
+            colorName = "565";
+            break;
+        case kAlpha_8_SkColorType:
+            colorName = "Alpha8";
+            break;
+        default:
+            colorName = "Unknown";
+    }
+    fName.printf("DecodeSubset_%dx%d_%s_%s", fDivisor, fDivisor,
+            baseName.c_str(), colorName);
+    
+    // Perform the decode setup
+    SkAutoTUnref<SkData> encoded(SkData::NewFromFileName(path.c_str()));
+    fStream.reset(new SkMemoryStream(encoded));
+    fDecoder.reset(SkImageDecoder::Factory(fStream));
+}
+
+const char* DecodingSubsetBench::onGetName() {
+    return fName.c_str();
+}
+
+bool DecodingSubsetBench::isSuitableFor(Backend backend) {
+    return kNonRendering_Backend == backend;
+}
+    
+void DecodingSubsetBench::onDraw(const int n, SkCanvas* canvas) {
+    for (int i = 0; i < n; i++) {
+        int w, h;
+        fDecoder->buildTileIndex(fStream->duplicate(), &w, &h);
+        // Divide the image into subsets and decode each subset
+        const int sW  = w / fDivisor;
+        const int sH = h / fDivisor;
+        for (int y = 0; y < h; y += sH) {
+            for (int x = 0; x < w; x += sW) {
+                SkBitmap bitmap;
+                SkIRect rect = SkIRect::MakeXYWH(x, y, sW, sH);
+                fDecoder->decodeSubset(&bitmap, rect, fColorType);
+            }
+        }
+    }
+}