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Scale skin_width by PhysicsLengthUnit#898

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Jondolf merged 3 commits into
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scale-skin-width
Nov 26, 2025
Merged

Scale skin_width by PhysicsLengthUnit#898
Jondolf merged 3 commits into
mainfrom
scale-skin-width

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@Jondolf

@Jondolf Jondolf commented Nov 26, 2025

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Objective

The move_and_slide_2d example sometimes gets stuck on ramps due to a skin width that is too small. This is because it's not accounting for the scale of the world.

Solution

Scale the skin_width by PhysicsLengthUnit. This appears to fix the problem.

Testing

Ran the move_and_slide_2d example.

@Jondolf Jondolf added D-Trivial Nice and straightforward! A great choice to get started with Avian A-Character-Controller Relates to character controllers C-Refinement Improves quality or results in some way, without fixing a clear bug or adding new functionality labels Nov 26, 2025
janhohenheim
janhohenheim reviewed Nov 26, 2025
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Is it intentionally not scaled here?

avian/src/character_controller/move_and_slide.rs

Line 535 in 980e4c5

config.skin_width * 2.0,

@janhohenheim

janhohenheim commented Nov 26, 2025

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Maybe add a note for future us to always scale the input by the length unit :)

avian/src/character_controller/move_and_slide.rs

Line 772 in 980e4c5

fn pull_back(hit: ShapeHitData, dir: Dir, skin_width: Scalar) -> Scalar {

@Jondolf

Jondolf commented Nov 26, 2025

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Is it intentionally not scaled here?

It's passed to intersections, which scales the given prediction distance. Though it is maybe a bit confusing, perhaps we shouldn't scale any method args and only scale the skin_width stored in the config

@janhohenheim

janhohenheim commented Nov 26, 2025

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Can we add a note here that the inner called functions perform the scaling? Otherwise it looks like we missed it and we might PR it in accidentally in the future

avian/src/character_controller/move_and_slide.rs

Line 869 in 980e4c5

config.skin_width,

@Jondolf Jondolf merged commit d72c48b into main Nov 26, 2025
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@Jondolf Jondolf deleted the scale-skin-width branch November 26, 2025 15:11
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A-Character-Controller Relates to character controllers C-Refinement Improves quality or results in some way, without fixing a clear bug or adding new functionality D-Trivial Nice and straightforward! A great choice to get started with Avian

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@Jondolf @janhohenheim