Uploaded April 2025 | Updated September 2026, 5 days ago

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Unity's built-in physics system works well for most games, but sometimes you need more control over how collisions behave. In this video, we explore Unity’s `ContactModifyEvent` which lets you intercept and modify physics contacts at runtime — even while the solver is running across multiple threads. You'll learn how to ignore contacts based on position or direction, implement one-way walls using dot products, simulate conveyor belts by injecting tangential velocity, and track which triangles in a mesh collider were touched during collision. We also cover best practices for thread safety, using data structures like `ConcurrentHashSet` to collect contact info without breaking Unity’s multithreaded physics constraints. If you're building gameplay systems that need custom collision behavior — or you're just curious how deep Unity's physics hooks go — this video is for you.

More Reading: medium.com/waveaccess/contacts-modification-api-in-unity-d65deba6f7c

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▬ Contents of this video ▬▬▬▬▬▬▬▬▬▬

0:00 Changing Contact Velocity
4:18 Pass Through Colliders
6:28 Filtering Mesh Triangles

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*Assets Shown In This Video* _(Affiliate Links)_
All in 1 3D Shader = assetstore.unity.com/packages/vfx/shaders/all-in-1-3d-shader-316173?aid=1101lw3sv
Beautify - assetstore.unity.com/packages/vfx/shaders/fullscreen-camera-effects/beautify-3-advanced-post-processing-233073?aid=1101lw3sv
Umbra Soft Shadows - assetstore.unity.com/packages/vfx/shaders/fullscreen-camera-effects/umbra-soft-shadows-better-directional-contact-shadows-for-urp-282485?aid=1101lw3sv
Wingman - assetstore.unity.com/packages/tools/utilities/wingman-your-inspector-s-best-friend-303181?aid=1101lw3sv
Favorites Window - assetstore.unity.com/packages/tools/utilities/favorites-window-123487?aid=1101lw3sv
Logwin - assetstore.unity.com/packages/tools/utilities/logwin-log-debug-values-tracker-149558?aid=1101lw3sv
TimeScale Toolbar - assetstore.unity.com/packages/tools/utilities/timescale-toolbar-291564?aid=1101lw3sv
Odin - assetstore.unity.com/packages/tools/utilities/odin-inspector-and-serializer-89041?aid=1101lw3sv?aid=1101lw3sv
Odin Validator - assetstore.unity.com/packages/tools/utilities/odin-validator-227861?aid=1101lw3sv
Hot Reload: assetstore.unity.com/packages/tools/utilities/hot-reload-edit-code-without-compiling-254358?aid=1101lw3sv
Better Hierarchy: assetstore.unity.com/packages/tools/utilities/better-hierarchy-272963?aid=1101lw3sv
Better Transform: assetstore.unity.com/packages/tools/utilities/better-transform-size-notes-global-local-workspace-child-parent--276554?aid=1101lw3sv
Better Mesh Filter: assetstore.unity.com/packages/tools/utilities/better-mesh-filter-266489?aid=1101lw3sv
Editor Console Pro: assetstore.unity.com/packages/tools/utilities/editor-console-pro-11889?aid=1101lw3sv
Any Object Finder: assetstore.unity.com/packages/tools/utilities/any-object-finder-286455?aid=1101lw3sv
Clipper PRO: assetstore.unity.com/packages/tools/utilities/clipper-pro-the-ultimate-clipboard-277112?aid=1101lw3sv
Kybernetic Tools: assetstore.unity.com/publishers/16747?aid=1101lw3sv
Sisus Tools: assetstore.unity.com/publishers/41398?aid=1101lw3sv
Prime Tween - assetstore.unity.com/packages/tools/animation/primetween-high-performance-animations-and-sequences-2529607?aid=1101lw3s
Rabbit Logger - assetstore.unity.com/packages/tools/utilities/rabbit-logger-305396?aid=1101lw3s

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