Add subsetting to SkScanlineDecoder

dm/DMSrcSink.cpp

Index: dm/DMSrcSink.cpp
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 88371a8e28fdf68e1e0e5e041588a3a475e4adc1..6bed84d2166086a11aef99070b6edc4b152d3a5e 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -8,7 +8,7 @@
 #include "DMSrcSink.h"
 #include "SamplePipeControllers.h"
 #include "SkCodec.h"
-#include "SkCodecTools.h"
+#include "SkCodecPriv.h"
 #include "SkCommonFlags.h"
 #include "SkData.h"
 #include "SkDocument.h"
@@ -86,7 +86,7 @@ static SkBitmapRegionDecoderInterface* create_brd(Path path,
         SkBitmapRegionDecoderInterface::Strategy strategy) {
     SkAutoTUnref<SkData> encoded(SkData::NewFromFileName(path.c_str()));
     if (!encoded) {
-        return NULL;
+        return nullptr;
     }
     return SkBitmapRegionDecoderInterface::CreateBitmapRegionDecoder(new SkMemoryStream(encoded),
             strategy);
@@ -244,7 +244,7 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
     if (!encoded) {
         return SkStringPrintf("Couldn't read %s.", fPath.c_str());
     }
-    SkAutoTDelete<SkCodec> codec(NULL);
+    SkAutoTDelete<SkCodec> codec(nullptr);
     if (kScaledCodec_Mode == fMode) {
         codec.reset(SkScaledCodec::NewFromData(encoded));
         // TODO (msarett): This should fall through to a fatal error once we support scaled
@@ -400,9 +400,6 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
                 return SkStringPrintf("Image(%s) is too large (%d x %d)\n", fPath.c_str(),
                         largestSubsetDecodeInfo.width(), largestSubsetDecodeInfo.height());
             }
-            const size_t rowBytes = decodeInfo.minRowBytes();
-            char* buffer = new char[largestSubsetDecodeInfo.height() * rowBytes];
-            SkAutoTDeleteArray<char> lineDeleter(buffer);
             for (int col = 0; col < divisor; col++) {
                 //currentSubsetWidth may be larger than subsetWidth for rightmost subsets
                 const int currentSubsetWidth = (col + 1 == divisor) ?
@@ -414,10 +411,13 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
                             subsetHeight + extraY : subsetHeight;
                     const int y = row * subsetHeight;
                     //create scanline decoder for each subset
-                    if (SkCodec::kSuccess != codec->startScanlineDecode(decodeInfo, NULL, colorPtr,
-                                                                        colorCountPtr)
-                            // TODO (msarett): Support this mode for all scanline orderings.
-                            || SkCodec::kTopDown_SkScanlineOrder != codec->getScanlineOrder()) {
+                    SkCodec::Options options;
+                    SkIRect subset = SkIRect::MakeXYWH(x, 0, currentSubsetWidth, h);
+                    options.fSubset = &subset;
+                    // TODO (msarett): Support this mode for all scanline orderings.
+                    if (SkCodec::kSuccess != codec->startScanlineDecode(decodeInfo, &options,
+                            colorPtr, colorCountPtr) ||
+                            SkCodec::kTopDown_SkScanlineOrder != codec->getScanlineOrder()) {
                         if (x == 0 && y == 0) {
                             //first try, image may not be compatible
                             return Error::Nonfatal("Could not start top-down scanline decoder");
@@ -433,22 +433,14 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
                     codec->skipScanlines(y);
 
                     //create and set size of subsetBm
-                    SkBitmap subsetBm;
+                    SkBitmap bitmap;
                     SkIRect bounds = SkIRect::MakeWH(currentSubsetWidth, currentSubsetHeight);
-                    SkAssertResult(largestSubsetBm.extractSubset(&subsetBm, bounds));
-                    SkAutoLockPixels autlockSubsetBm(subsetBm, true);
-                    codec->getScanlines(buffer, currentSubsetHeight, rowBytes);
-
-                    const size_t bpp = decodeInfo.bytesPerPixel();
-                    char* bufferRow = buffer;
-                    for (int subsetY = 0; subsetY < currentSubsetHeight; ++subsetY) {
-                        memcpy(subsetBm.getAddr(0, subsetY), bufferRow + x*bpp,
-                                currentSubsetWidth*bpp);
-                        bufferRow += rowBytes;
-                    }
-
-                    subsetBm.notifyPixelsChanged();
-                    canvas->drawBitmap(subsetBm, SkIntToScalar(x), SkIntToScalar(y));
+                    SkAssertResult(largestSubsetBm.extractSubset(&bitmap, bounds));
+                    SkAutoLockPixels autolock(bitmap, true);
+                    codec->getScanlines(bitmap.getAddr(0, 0), currentSubsetHeight,
+                            bitmap.rowBytes());
+                    bitmap.notifyPixelsChanged();
+                    canvas->drawBitmap(bitmap, SkIntToScalar(x), SkIntToScalar(y));
                 }
             }
             break;