tree 17579347d627ede9bdc4e675b22202f4191190f9
parent 8c0144ccb17220db9d5140ef5ee85d5bc7837513
author scroggo <scroggo@chromium.org> 1437574580 -0700
committer Commit bot <commit-bot@chromium.org> 1437574580 -0700

Add the ability to decode a subset to SkCodec

This allows codecs that support subsets natively (i.e. WEBP) to do so.

Add a field on SkCodec::Options representing the subset.

Add a method on SkCodec to find a valid subset which approximately
matches a desired subset.

Implement subset decodes in SkWebpCodec.

Add a test in DM for decoding subsets.
Notice that we only start on even boundaries. This is due to the
way libwebp's API works. SkWEBPImageDecoder does not take this into
account, which results in visual artifacts.

FIXME: Subsets with scaling are not pixel identical, but close. (This
may be fine, though - they are not perceptually different. We'll just
need to mark another set of images in gold as valid, once
https://skbug.com/4038 is fixed, so we can tests scaled webp without
generating new images on each run.)

Review URL: https://codereview.chromium.org/1240143002