commit f7dc9fa74af1107a161755d004e4ae31a54e756b
author Xianzhu Wang <wangxianzhu@chromium.org> Tue Jul 26 05:06:42 2022
committer Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> Tue Jul 26 05:23:48 2022
tree bf27e36e16b1a7cd1b11e841adb5cdb339da2a69
parent 6808a6b42652b5f4786a6057a8e7f6778987fb67

Set contents_opaque(false) if the background color is transparent

Previously if a layer's background was transparent and the layer is
opaque, we used the layer_tree_host's background as
SafeOpaqueBackgroundColor(). One of the usages of
SafeOpaqueBackgroundColor() is to fill the otherwise translucent
antialiased pixels along the edge of rasterization, when the layer
has non-integral raster transform, to ensure the layer is still
fully opaque. However, the color might be dramatically
different from the normal color in the layer, causing edge artifacts.

Now set contents_opaque(false) in the case.

The case of opaque layer not having a background color only happens
in cases such as the layer has an opaque background image. In such
cases, using any heuristic color as the
SafeOpaqueBackgroundColor() may be inappropriate because the color
may be visibly different from the background image.

This also prevents seams between adjacent image layers when the layers
layer have non-integral to-screen transforms.

Bug: 1330509
Change-Id: I91edeb1c02da5eaa38ea0431f0559775b273f418
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3779000
Reviewed-by: Stefan Zager <szager@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1028113}