Add image decoding mode to DM.

dm/DMImageTask.cpp

Index: dm/DMImageTask.cpp
diff --git a/dm/DMImageTask.cpp b/dm/DMImageTask.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..1657984f1ee71d6ed4956320142aa9f1bf053619
--- /dev/null
+++ b/dm/DMImageTask.cpp
@@ -0,0 +1,78 @@
+#include "DMImageTask.h"
+#include "DMUtil.h"
+#include "DMWriteTask.h"
+#include "SkImageDecoder.h"
+#include "SkRandom.h"
+
+#include <string.h>
+
+namespace DM {
+
+// This converts file names like "mandrill_128.r11.ktx" into
+// "mandrill-128-r11_ktx" or "mandrill-128-r11-5-subsets_ktx".
+static SkString task_name(SkString filename, int subsets) {
+    const char* ext = strrchr(filename.c_str(), '.');
+    SkString name(filename.c_str(), ext - filename.c_str());
+    if (subsets > 0) {
+        name.appendf("_%d_subsets", subsets);
+    }
+    name = FileToTaskName(name);  // Promote any stray '.' in the filename to '_'.
+    name.append(ext);             // Tack on the extension, including the '.'.
+    return FileToTaskName(name);  // Promote that last '.' to '_', other '_' to '-'.
+}
+
+ImageTask::ImageTask(Reporter* r, TaskRunner* t, const SkData* encoded, SkString name, int subsets)
+    : CpuTask(r, t)
+    , fEncoded(SkRef(encoded))
+    , fName(task_name(name, subsets))
+    , fSubsets(subsets) {}
+
+void ImageTask::draw() {
+    if (fSubsets == 0) {
+        // Decoding the whole image is considerably simpler than decoding subsets!
+        SkBitmap bitmap;
+        if (!SkImageDecoder::DecodeMemory(fEncoded->data(), fEncoded->size(), &bitmap)) {
+            return this->fail("Can't DecodeMemory");
+        }
+        this->spawnChild(SkNEW_ARGS(WriteTask, (*this, "image", bitmap)));
+        return;
+    }
+
+    SkMemoryStream stream(fEncoded->data(), fEncoded->size());
+    SkAutoTDelete<SkImageDecoder> decoder(SkImageDecoder::Factory(&stream));
+    if (!decoder) {
+        return this->fail("Can't find good decoder.");
+    }
+
+    int w,h;
+    if (!decoder->buildTileIndex(&stream, &w, &h) || w*h == 1) {
+        return;  // Subset decoding is not always supported.
+    }
+
+    SkBitmap composite;
+    composite.allocN32Pixels(w,h);  // We're lazy here and just always use native 8888.
+    composite.eraseColor(SK_ColorTRANSPARENT);
+    SkCanvas canvas(composite);
+
+    SkRandom rand;
+    for (int i = 0; i < fSubsets; i++) {
+        SkIRect rect;
+        do {
+            rect.fLeft   = rand.nextULessThan(w);
+            rect.fTop    = rand.nextULessThan(h);
+            rect.fRight  = rand.nextULessThan(w);
+            rect.fBottom = rand.nextULessThan(h);
+            rect.sort();
+        } while (rect.isEmpty());
+
+        SkBitmap subset;
+        if (!decoder->decodeSubset(&subset, rect, kN32_SkColorType)) {
+            return this->fail("Could not decode subset.");
+        }
+        canvas.drawBitmap(subset, SkIntToScalar(rect.fLeft), SkIntToScalar(rect.fTop));
+    }
+    canvas.flush();
+    this->spawnChild(SkNEW_ARGS(WriteTask, (*this, "image", composite)));
+}
+
+}  // namespace DM