# Help on concave collision

**URL:** <https://forum.kirupa.com/t/help-on-concave-collision/272724>\
**Category:** Uncategorized\
**Created:** [October 8, 2008, 12:42am UTC](https://forum.kirupa.com/t/help-on-concave-collision/272724 "2008-10-08T00:42:09Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![cnboy0212](https://avatars.discourse-cdn.com/v4/letter/c/bc79bd/32.png) [@cnboy0212](https://forum.kirupa.com/u/cnboy0212)\
**Post date:** [October 8, 2008, 12:42am UTC](https://forum.kirupa.com/t/help-on-concave-collision/272724/1 "2008-10-08T00:42:09Z")

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well i learned how to triangulate simple polygon into smaller triangles,but i still got a problem with the reaction. To bounce an object back after it hits another object with convex shape,i used the separating axis theorem.but if i triangulate a concave shape and its divided in to many triangles,and when an moving object hittings its,if i use the SAT to do the reaction sometimes i might just be bouncing between the 2 triangle inside the shape(depends on where the object hits).any one know how to handle the reaction?