Adding new benchmark to test image decoding performance.

bench/DecodingBench.cpp

+/*
+ * 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 "DecodingBench.h"
+#include "SkImageDecoder.h"
+#include "SkOSFile.h"
+#include "SkStream.h"
+
+/*
+ *
+ * This benchmark is designed to test the performance of image decoding.
+ * It is invoked from the nanobench.cpp file.
+ *
+ */
+DecodingBench::DecodingBench(SkString path, SkColorType colorType)
+    : fPath(path)
+    , fColorType(colorType)
+{
+    // 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("Decode_%s_%s", baseName.c_str(), colorName);
+}
+
+const char* DecodingBench::onGetName() {
+    return fName.c_str();
+}
+
+bool DecodingBench::isSuitableFor(Backend backend) {
+    return kNonRendering_Backend == backend;
+}
+    
+void DecodingBench::onDraw(const int n, SkCanvas* canvas) {
+    // Perform setup for the decode
+    SkAutoTDelete<SkStreamRewindable> stream(

[scroggo, 2015/02/12 19:53:28]

I was thinking more like what DM does: Read the file into an SkData (using
SkData::NewFromFileName(fPath.c_str())). Then read from  an SkMemoryStream. Then
we don't include reading from the file system in the loops. (We could even
create the SkData in the constructor in in predraw.)

[msarett, 2015/02/12 22:05:45]

Yes this makes significantly more sense.

+            SkStream::NewFromFile(fPath.c_str()));
+    SkImageDecoder* decoder = SkImageDecoder::Factory(stream);
+    SkBitmap bitmap;
+    
+    // Decode each image file n times
+    for (int i = 0; i < n; i++) {
+        decoder->decode(stream, &bitmap, fColorType,
+                SkImageDecoder::kDecodePixels_Mode);
+        stream->rewind();
+    }
+    
+    // Clean up after the decode
+    delete decoder;
+}