commit 91c22b2ea6bd13a31321ead01645467f21858cd0
author msarett <msarett@google.com> Mon Feb 22 12:27:46 2016 -0800
committer Commit bot <commit-bot@chromium.org> Mon Feb 22 12:27:46 2016 -0800
tree 99f66c26c87bbcade9c7eac84099e2fae7c01cd5
parent 7499e69d9991a113c452a2a44a10078df41f3758

Use new jpeg_crop_scanlines() API to optimize jpeg subset decodes

This was adapted from:
https://codereview.chromium.org/1530933003

Subset Decode Runtime (Original / Optimized) on Nexus 6P
TopLeft     0.51x
TopRight    0.56x
Middle      0.71x
BottomLeft  0.79x
BottomRight 0.79x

BUG=skia:4256
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1719073002

Review URL: https://codereview.chromium.org/1719073002

dm/DMSrcSink.cpp

diff --git a/dm/DMSrcSink.cpp b/dm/DMSrcSink.cpp
index 7ccaf22..bd881e8 100644
--- a/dm/DMSrcSink.cpp
+++ b/dm/DMSrcSink.cpp
@@ -522,6 +522,31 @@
             canvas->drawBitmap(bitmap, 0, 0);
             break;
         }
+        case kCroppedScanline_Mode: {
+            const int width = decodeInfo.width();
+            const int height = decodeInfo.height();
+            // This value is chosen because, as we move across the image, it will sometimes
+            // align with the jpeg block sizes and it will sometimes not.  This allows us
+            // to test interestingly different code paths in the implementation.
+            const int tileSize = 36;
+
+            SkCodec::Options opts;
+            SkIRect subset;
+            for (int x = 0; x < width; x += tileSize) {
+                subset = SkIRect::MakeXYWH(x, 0, SkTMin(tileSize, width - x), height);
+                opts.fSubset = &subset;
+                if (SkCodec::kSuccess != codec->startScanlineDecode(decodeInfo, &opts,
+                        colorPtr, colorCountPtr)) {
+                    return "Could not start scanline decoder.";
+                }
+
+                codec->getScanlines(bitmap.getAddr(x, 0), height, bitmap.rowBytes());
+            }
+
+            premultiply_if_necessary(bitmap);
+            canvas->drawBitmap(bitmap, 0, 0);
+            break;
+        }
         case kSubset_Mode: {
             // Arbitrarily choose a divisor.
             int divisor = 2;