tree ad4affc574754deb8d83be988e32af26d37cceb5
parent db80cbe34ad7ea44aea86e47d76034cfa716afd7
author Leon Scroggins III <scroggo@google.com> 1544455758 -0500
committer Skia Commit-Bot <skia-commit-bot@chromium.org> 1544540868 +0000

Treat kWEBP encode with quality=100 as lossless

In SkEncodeImage and friends, treat quality of 100 as a lossless encode
when using kWEBP. This seems a good fit for the intent - which is
presumably to save the highest quality image. This also matches
Chromium's blink::ImageEncoder::ComputeWebpOptions, which treats a
quality of 1 (on a float scale from 0 to 1) as a lossless encode.

FWIW, Chromium has had this behavior since
https://codereview.chromium.org/1937433002, in response to
crbug.com/523098. The goal is to "maintain sharpness to
match the JPEG encoder behavior (use WEBP lossless encoding)".

Add a test to verify the new behavior. This requires making tests
depend on libwebp to use WebPGetFeatures, since the Skia API does not
provide a way to determine whether an encoded webp file was encoded
lossless-ly or lossily.

Bug: skia:8586
Change-Id: Ie9e09c2f7414ab701d696c4ad9edf405868a716f
Reviewed-on: https://skia-review.googlesource.com/c/175823
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Reviewed-by: Mike Reed <reed@google.com>