Subset decoding benchmarks

bench/CodecSubsetBench.h

Index: bench/CodecSubsetBench.h
diff --git a/bench/CodecSubsetBench.h b/bench/CodecSubsetBench.h
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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 "Benchmark.h"
+#include "SkImageDecoder.h"
+#include "SkImageInfo.h"
+#include "SkStream.h"
+#include "SkString.h"
+
+/*
+ *
+ * This benchmark is designed to test the performance of subset decoding.
+ *
+ */
+class CodecSubsetBench : public Benchmark {
+public:
+
+    // Defines the style of the subset decoding benchmark.
+    enum SubsetMode {
+        // Use an input width, height, left, and top to decode a single subset.
+        // Must specify: subsetWidth, subsetHeight, offsetLeft, offsetTop

[scroggo, 2015/05/29 15:36:03]

It might be clearer to have different constructors for different modes (or even
a factory), rather than having parameters which are only meaningful in the right
mode.

[msarett, 2015/06/01 14:03:25]

I am splitting the benchmark into separate subclasses.

+        kSingle_SubsetMode,
+
+        // Use a divisor to decode the entire image in a grid of divisor x divisor blocks.
+        // Must specify: divisor
+        kDivisor_SubsetMode,
+
+        // Use input dimensions to decode the entire image where each block is susbetW x subsetH.
+        // Must specify: subsetWidth, subsetHeight
+        kTranslate_SubsetMode,
+
+        // Choose subsets to mimic a user zooming out on a photo

[scroggo, 2015/05/29 15:36:03]

nit: zooming in* ?

[msarett, 2015/06/01 14:03:25]

It mimics zooming out.  The subsets get bigger each time, meaning that more of
the image is being displayed (and it has be scaled down in a subsequent step).

Of course zooming in may be a more likely use case, and the performance results
should be identical to those if we started with big subsets and got smaller.

I'm changing the comment to indicate that it measures both.

+        // Must specify: subsetWidth, subsetHeight
+        kScale_SubsetMode
+    };
+
+    CodecSubsetBench(SkString* path,
+                     SubsetMode subsetMode,
+                     SkColorType colorType,
+                     uint32_t subsetWidth,
+                     uint32_t subsetHeight,
+                     uint32_t offsetLeft,
+                     uint32_t offsetTop,
+                     uint32_t divisor,
+                     bool useCodec);
+
+protected:
+    const char* onGetName() override;
+    bool isSuitableFor(Backend backend) override;
+    void onDraw(const int n, SkCanvas* canvas) override;
+
+private:
+
+    SkString fName;
+    SubsetMode fSubsetMode;
+    SkColorType fColorType;
+    const uint32_t fSubsetWidth;
+    const uint32_t fSubsetHeight;
+    const uint32_t fOffsetLeft;
+    const uint32_t fOffsetTop;
+    const uint32_t fDivisor;
+    const bool fUseCodec;
+    SkAutoTDelete<SkMemoryStream> fStream;
+    typedef Benchmark INHERITED;
+};