gl_engine/tessellator: Improve stroke tessellation quality #3903
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Pull Request Overview
This PR improves stroke tessellation quality in the GL engine by enhancing segment count calculations during the join process. The changes ensure that the transformation matrix is properly considered when computing tessellation segments, resulting in smoother and more accurate stroke rendering that more closely matches the WebGPU engine's output.
Key Changes:
- Updated tessellation methods (
lineTo,close,cap,join,round) to accept and use the transformation matrix parameter - Modified segment count calculation to apply the transformation matrix before computing segments
- Ensured consistent parameter passing throughout the stroke tessellation pipeline
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| tvgGlTessellator.h | Updated method signatures to include Matrix parameter for improved tessellation calculations |
| tvgGlTessellator.cpp | Implemented Matrix parameter threading through tessellation methods and updated segment calculation logic |
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@wenjieshen |
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@SergeyLebedkin |
hermet
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@wenjieshen How about retain scale value from Stroker() constructor and access that member value from the round()? Logic will be much simple Thanks.
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@SergeyLebedkin @hermet Thank you for your patience. I checked there is no regression occurring. I think this PR is ready. |
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@wenjieshen last feedback thanks!
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| // Fixme: just use bezier curve to calculate step count | ||
| auto count = Bezier(prev, curr, radius()).segments(); | ||
| auto count = (Bezier(prev, curr, radius()) * mScale).segments(); |
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"multiply" a point on a Bézier curve isn't in the standard sense; Please use this way:
Bezier(prev * mScale, curr * mScale, radius() * mScale).segment()
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This patch partially addresses issue thorvg#3665 by improving stroke tessellation quality in the GL engine. The revised algorithm produces smoother and more accurate stroke rendering, aligning more closely with the WebGPU engine’s output. Implementation Details: Enhanced tessellation logic for more precise segment count calculation. Updated cubicTo() to pass the Transform matrix to round() for correct segment computation. Current Status: Resolves the main stroke quality issue from thorvg#3665. The odd-even fill issue described in thorvg#3668 will be addressed in a future update. Related Issues: Partially resolves: thorvg#3665 (GL/WG: poor stroke quality) Related: thorvg#3668 (Engines: excessive stroke width causes inconsistency)
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I ran the Lottie examples five times on each branch (tested on macOS):
Interestingly, this branch shows slightly higher FPS, which isn’t expected. |
This is explained by the fact that it is most likely that the reduction in the size of the Bézier curves is more common than the scale-up, which leads to a reduction in the number of points for tessellation |
Summary
This patch partially resolves issue #3665
by improving stroke tessellation quality in the GL engine.
The updated algorithm produces smoother and more accurate stroke rendering, achieving visual results closer to the WebGPU engine.
Changes
Improved segment count calculation in the tessellation join process.
Updated the member function
lineToandcloseto imitatecubicTologic, passing the Transform matrix as a parameter toroundto ensure proper segment computation.Current Status
Fixes the basic stroke quality problem described in #3665.
The odd–even rendering issue mentioned in #3668
remains and will be addressed in a future patch.
Related Issues
Partially resolves: #3665 (GL/WG: poor stroke quality)
Related: #3668 (Engines: excessive stroke width causes visual inconsistency)