Use possible read_partial_scanlines() API in SkJpegCodec

dm/DMSrcSink.cpp

Index: dm/DMSrcSink.cpp
diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index e27628ad043aeedc9676dfd1a00187c843ad2fa8..efffc8f06bef6306e702857e39c4848f37fc3cae 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -372,54 +372,39 @@ Error CodecSrc::draw(SkCanvas* canvas) const {
             canvas->drawBitmap(bitmap, 0, 0);
             break;
         }
-        case kStripe_Mode: {
+        case kTile_Mode: {
+            const int width = decodeInfo.width();
             const int height = decodeInfo.height();
             // This value is chosen arbitrarily.  We exercise more cases by choosing a value that
             // does not align with image blocks.
-            const int stripeHeight = 37;
-            const int numStripes = (height + stripeHeight - 1) / stripeHeight;
+            const int tileSize = 37;
+            const int tileWidth = (width + tileSize - 1) / tileSize;
+            const int tileHeight = (height + tileSize - 1) / tileSize;
 
-            // Decode odd stripes
-            if (SkCodec::kSuccess != codec->startScanlineDecode(decodeInfo, NULL, colorPtr,
-                                                                colorCountPtr)
-                    || SkCodec::kTopDown_SkScanlineOrder != codec->getScanlineOrder()) {
-                // This mode was designed to test the new skip scanlines API in libjpeg-turbo.
-                // Jpegs have kTopDown_SkScanlineOrder, and at this time, it is not interesting
-                // to run this test for image types that do not have this scanline ordering.
-                return Error::Nonfatal("Could not start top-down scanline decoder");
-            }
-
-            for (int i = 0; i < numStripes; i += 2) {
-                // Skip a stripe
-                const int linesToSkip = SkTMin(stripeHeight, height - i * stripeHeight);
-                codec->skipScanlines(linesToSkip);
+            SkCodec::Options opts;
+            SkIRect subset;
+            for (int tileX = 0; tileX < tileWidth; tileX++) {
+                const int startX = tileX * tileSize;
+                subset = SkIRect::MakeXYWH(startX, 0, SkTMin(tileSize, width - startX), height);
+                opts.fSubset = &subset;
+                for (int tileY = 0; tileY < tileHeight; tileY++) {
+                    if (SkCodec::kSuccess != codec->startScanlineDecode(decodeInfo, &opts,
+                            colorPtr, colorCountPtr) ||
+                            SkCodec::kTopDown_SkScanlineOrder != codec->getScanlineOrder()) {
+                        if (0 == tileY && 0 == tileX) {
+                            return Error::Nonfatal("Could not start top-down scanline decoder");
+                        }
+                        return "Could not restart scanline decoder.";
+                    }
 
-                // Read a stripe
-                const int startY = (i + 1) * stripeHeight;
-                const int linesToRead = SkTMin(stripeHeight, height - startY);
-                if (linesToRead > 0) {
-                    codec->getScanlines(bitmap.getAddr(0, startY), linesToRead, bitmap.rowBytes());
+                    const int startY = tileY * tileSize;
+                    codec->skipScanlines(startY);
+                    const int linesToGet = SkTMin(tileSize, height - startY);
+                    codec->getScanlines(bitmap.getAddr(startX, startY), linesToGet,
+                            bitmap.rowBytes());
                 }
             }
 
-            // Decode even stripes
-            const SkCodec::Result startResult = codec->startScanlineDecode(decodeInfo, nullptr,
-                    colorPtr, colorCountPtr);
-            if (SkCodec::kSuccess != startResult) {
-                return "Failed to restart scanline decoder with same parameters.";
-            }
-            for (int i = 0; i < numStripes; i += 2) {
-                // Read a stripe
-                const int startY = i * stripeHeight;
-                const int linesToRead = SkTMin(stripeHeight, height - startY);
-                codec->getScanlines(bitmap.getAddr(0, startY), linesToRead, bitmap.rowBytes());
-
-                // Skip a stripe
-                const int linesToSkip = SkTMin(stripeHeight, height - (i + 1) * stripeHeight);
-                if (linesToSkip > 0) {
-                    codec->skipScanlines(linesToSkip);
-                }
-            }
             canvas->drawBitmap(bitmap, 0, 0);
             break;
         }