tree 2dde99872db9958cce35d3bc920860161e95aea1
parent f64e4075f2f8164cc36a9d10b04bb69dbb8588e4
author Leon Scroggins <scroggo@google.com> 1607538797 -0500
committer Skia Commit-Bot <skia-commit-bot@chromium.org> 1607617448 +0000

Fix blending bug in animated webp decodes

Bug: webp:490

Depending on the encoded image, SkWebpCodec may need to blend the
the output from libwebp with the prior frame. It does so using the
method blend_line, which expects the libwebp output to be unpremul.

Prior to this commit, SkWebpCodec sometimes told libwebp to premultiply,
and then passed that premultiplied data to blend_line, which
premultiplied again.

Use webpInfo's alphaType to decide whether to premultiply. Consolidate
choosing its alphaType into one block. The functional difference is that
if (blendWithPrevFrame), we no longer premul if the dst is kPremul.

Move declaration of webDst to where it's used.

Add a test.

Change-Id: Ic0cfb4d918c2ab434c6787ed5a532c4d1e67fa17
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/342618
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Derek Sollenberger <djsollen@google.com>
Auto-Submit: Leon Scroggins <scroggo@google.com>