Repository navigation
[CP-beta]Implement UberSDF lines to replace LineContents-based AA lines - #189537
Conversation
…er#188514) Implements UberSDF lines, which are drawn by making an UberSDF rect or roundrect and applying a translation/rotation transform. Fixes flutter#188329 Fixes flutter#188911 Fixes flutter#188593 (by replacing and obsoleting LineContents) After this, LineContents can be removed entirely. I will do this in a follow-up to keep this PR focused on the UberSDF line implementation. Adds a new golden test that draws lines with varying caps/angles/opacities. Before: <img width="1024" height="800" alt="Screenshot 2026-06-24 at 10 46 48 AM" src="/sitelet?url=https%3A%2F%2Fgithub.com%2Fflutter%2Fflutter%2Fpull%2F%253Ca%2520href%3D"/sitelet?url=https%3A%2F%2Fgithub.com%2Fuser-attachments%2Fassets%2F2d981538-5120-4cf0-9bc0-d8d43e41b03c">https://github.com/user-attachments/assets/2d981538-5120-4cf0-9bc0-d8d43e41b03c" /> After: <img width="1024" height="800" alt="Screenshot 2026-06-24 at 10 47 56 AM" src="/sitelet?url=https%3A%2F%2Fgithub.com%2Fflutter%2Fflutter%2Fpull%2F%253Ca%2520href%3D"/sitelet?url=https%3A%2F%2Fgithub.com%2Fuser-attachments%2Fassets%2Fa6f70277-a26a-46d4-b456-e482f7a964d3">https://github.com/user-attachments/assets/a6f70277-a26a-46d4-b456-e482f7a964d3" /> ## Pre-launch Checklist - [x] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [x] I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools. - [x] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [x] I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement]. - [x] I signed the [CLA]. - [x] I listed at least one issue that this PR fixes in the description above. - [x] I updated/added relevant documentation (doc comments with `///`). - [x] I added new tests to check the change I am making, or this PR is [test-exempt]. - [x] I followed the [breaking change policy] and added [Data Driven Fixes] where supported. - [x] All existing and new tests are passing. If you need help, consider asking for advice on the #hackers-new channel on [Discord]. If this change needs to override an active code freeze, provide a comment explaining why. The code freeze workflow can be overridden by code reviewers. See pinned issues for any active code freezes with guidance. **Note**: The Flutter team is currently trialing the use of [Gemini Code Assist for GitHub](https://developers.google.com/gemini-code-assist/docs/review-github-code). Comments from the `gemini-code-assist` bot should not be taken as authoritative feedback from the Flutter team. If you find its comments useful you can update your code accordingly, but if you are unsure or disagree with the feedback, please feel free to wait for a Flutter team member's review for guidance on which automated comments should be addressed. <!-- Links --> [Contributor Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#overview [AI contribution guidelines]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#ai-contribution-guidelines [Tree Hygiene]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md [test-exempt]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests [Flutter Style Guide]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md [Features we expect every widget to implement]: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#features-we-expect-every-widget-to-implement [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [breaking change policy]: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md [Data Driven Fixes]: https://github.com/flutter/flutter/blob/main/docs/contributing/Data-driven-Fixes.md
|
@b-luk please fill out the PR description above, afterwards the release team will review this request. |
|
This pull request was opened from and to a release candidate branch. This should only be done as part of the official Flutter release process. If you are attempting to make a regular contribution to the Flutter project, please close this PR and follow the instructions at Tree Hygiene for detailed instructions on contributing to Flutter. Reviewers: Use caution before merging pull requests to release branches. Ensure the proper procedure has been followed. |
There was a problem hiding this comment.
Code Review
This pull request refactors line, rectangle, and round rectangle rendering in Impeller to support SDF rendering and introduces a more robust mechanism for expanding shapes to a 1-pixel minimum size using ExpandToMinTransformedSize. Feedback focuses on handling edge cases, specifically: snapping extremely small line lengths to zero to prevent division-by-zero or overflow when calculating unit vectors, and using normalized/positive dimensions when calculating sizes and areas of potentially unnormalized rectangles to ensure correct physical dimensions and alpha scaling.
| Scalar line_length = p0.GetDistance(p1); | ||
| if (line_length == 0.0f && paint.stroke.cap == Cap::kButt) { | ||
| // 0 length line with butt caps is invisible. | ||
| return true; | ||
| } |
There was a problem hiding this comment.
If line_length is extremely small but non-zero (e.g., subnormal floats), dividing by it when calculating the unit vector u can cause floating-point overflow and result in NaN or infinity values. This can lead to rendering glitches or shader issues. Snapping line_length to 0.0f when it is less than or equal to kEhCloseEnough avoids this division-by-zero/overflow risk while maintaining correct rendering behavior.
| Scalar line_length = p0.GetDistance(p1); | |
| if (line_length == 0.0f && paint.stroke.cap == Cap::kButt) { | |
| // 0 length line with butt caps is invisible. | |
| return true; | |
| } | |
| Scalar line_length = p0.GetDistance(p1); | |
| if (line_length <= kEhCloseEnough) { | |
| line_length = 0.0f; | |
| } | |
| if (line_length == 0.0f && paint.stroke.cap == Cap::kButt) { | |
| // 0 length line with butt caps is invisible. | |
| return true; | |
| } |
| if (!min_local_size.IsFinite()) { | ||
| return std::nullopt; | ||
| } | ||
| Size current_size = GetSize(); |
There was a problem hiding this comment.
If this rectangle is unnormalized (having negative width or height), GetSize() will return negative components. Taking the maximum with min_local_size (which is positive) would incorrectly shrink the rectangle's physical size to min_local_size instead of preserving its original absolute size. Using GetPositive().GetSize() ensures we always work with the correct non-negative physical dimensions.
Size current_size = GetPositive().GetSize();| } | ||
|
|
||
| // Scale alpha based on expanded ratio. | ||
| Scalar alpha_scaling = rect.Area() / expanded->Area(); |
There was a problem hiding this comment.
If rect is unnormalized (i.e., has negative width or height), rect.Area() can return a negative value. This would cause alpha_scaling to be negative, incorrectly marking the rectangle as invisible. Using std::abs(rect.Area()) ensures the correct physical area is used for alpha scaling.
| Scalar alpha_scaling = rect.Area() / expanded->Area(); | |
| Scalar alpha_scaling = std::abs(rect.Area()) / expanded->Area(); |
afb9cec
into
flutter:flutter-3.47-candidate.0
This pull request is created by automatic cherry pick workflow
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.
This is the third in a set of 3 PRs (#188821, #189224, and #188514) that will be cherry picked in order to fix a set of line-related issues when Impeller with SDF rendering is enabled.
The first PR was cherry picked and merged with #189517
The second PR was cherry picked and merged with #189529
Issue Link:
What is the link to the issue this cherry-pick is addressing?
#188329
#188911
#188593
Impact Description:
What is the impact (ex. visual jank on Samsung phones, app crash, cannot ship an iOS app)?
Does it impact development (ex. flutter doctor crashes when Android Studio is installed),
or the shipping of production apps (the app crashes on launch).
This information is for domain experts and release engineers to understand the consequences of saying yes or no to the cherry pick.
Thin ines (including lines rendered with
canvas.drawLine, thin line-like rectangles rendered withcanvas.drawRect, and paths drawn withcanvas.drawPaththat consist of a single line or thin rectangle) have various highly visible rendering issues:This issue is present when impeller is enabled Impeller with SDF rendering. In the beta channel, Impeller with SDF rendering is the default when building apps for desktop platforms: macOS, Linux, and Windows.
Changelog Description:
Explain this cherry pick:
See best practices for examples.
flutter/188329, flutter/188911, flutter/188593: Multiple line rendering issues when Impeller with SDF rendering is enabled (default enabled on desktop platforms)
Workaround:
Is there a workaround for this issue?
Disable Impeller, falling back to Skia rendering.
Risk:
What is the risk level of this cherry-pick?
Test Coverage:
Are you confident that your fix is well-tested by automated tests?
Validation Steps:
What are the steps to validate that this fix works?
After all 3 PRs are cherry picked, verify the sample apps in the relevant issues (#188329 and #188911) render with expected opacity and with expected line widths.