LibWeb: Ensure scroll offset is applied to mask-images #4916
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
When recording the display list for a stacking context, the following operations (relevant to this bug) happened: * push a stacking context * as part of that push a None-value to the scroll frame id stack * apply filters * apply masking * paint recursively This meant that mask-images were always recorded without scroll frame id, causing them to be painted without any scroll offset. As a result mask-images would break as soon as the website using them was scrolled. Instead, push to the scroll frame id stack later to solve the problem: * push a stacking context * apply filters * apply masking * push a None-value to the scroll frame id stack * paint recursively
kalenikaliaksandr
approved these changes
May 29, 2025
Member
kalenikaliaksandr
left a comment
kalenikaliaksandr
left a comment
There was a problem hiding this comment.
the fix looks very reasonable. thanks for figuring that out!
gmta
approved these changes
May 29, 2025
Contributor
|
The test added here is flaking in CI: The result of the test seems to be a white blank page: |
Merged
Contributor
Author
Unfortunate, I even commented on that in #3646, but then couldn't reproduce it locally, so I thought it was fine. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
4 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
This fixes rendering bugs on https://www.fangamer.com/, https://null.com/games/bleakwood and https://t-shaped.nl/, among others. For a demonstration of the change, see the videos in #3646.
This is the third attempt at fixing this problem, the prior ones are in the stale PRs #3646 and #4312. However, this PR does not built on top of those changes. The approach used there was not correct. The original approach was to apply the scroll-offset of the mask-images while recording the display list. This does not work because a single display list may be rendered multiple times with different scroll offsets if the page does not cause any invalidation during scrolling.
As it turns out, applying of scroll-offsets to mask-images during display list replay is already present. It simply did not work because the scroll-frame ids were not set up correctly. For more details on the new approach see the commit message.