commit f461b6809f1fdb400f8a203a25001d2af121c088
author Xianzhu Wang <wangxianzhu@chromium.org> Wed Jul 20 20:04:28 2022
committer Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> Wed Jul 20 20:15:50 2022
tree 62a6853ba70fc4af6a4aa66057014405a074434f
parent 5fb15e04adca47cc972a2e4c665853aca6a1a5b9

Fix hairlines along edges of mask bounding box in masked layers

The following caused the hairlines:
1. Both the mask layer and the masked layer were under the same clip
   node which clips the layers to the mask bounding box;
2. The mask layer and the masked layer used different raster scales,
   and mapping clip rects between the layer space and the screen
   space caused errors. In the screen space, if the rect on the
   masked layer was bigger than the mask layer, pixels along the
   edges of the mask bounding box in the masked layer would
   be visible.

We can't force the same raster scale of the masked layer and the mask
layer because sometimes they are determined independently for the best
result of each layer. For example, we want to use the native scale for
surface layers (used for composited videos).

To solve the problem:
1. Change the output clip of the mask effect node and its isolation
   group node from the mask clip to the parent of the mask clip.
2. Change the painted result of the mask layer to the above output
   clip, so that the mask is no longer clipped by the mask bounding
   box.
3. Expand the bounds of the mask layer to make sure it always covers
   the masked layer.

This won't change the rendered result (except for slight change in
anti-aliased pixels when the surface/texture pixels are not 1:1
matching physical pixels) because the mask layer should be transparent
outside of the mask bounding box, and these transparent pixels should
mask off the pixels in the masked layers just like an exact mask clip.

Bug: 1171601
Change-Id: I85ff66e54eb67d8be01a5791d38622397da3cdf7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3742680
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1026396}