Fix contact generation with backface collision disabled #55073
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Replaced the previous implementation for backface collision handling (in test_axis function from SAT algorithm) with much simpler logic in the collision generation phase with face shapes, in order to get rid of wrong contacts when backface collision is disabled. Now it just ignores the generated collision if the contact normal is against the face normal, with a threshold to keep edge contacts. Added a special case for soft bodies to invert the collision instead of ignoring it, because for now it's the best solution to avoid soft bodies to go through concave shapes (they use small spheres). This might be replaced with a better algorithm for soft bodies later.
akien-mga
approved these changes
Nov 18, 2021
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Replaced the previous implementation for backface collision handling (in test_axis function from SAT algorithm) with much simpler logic in the collision generation phase with face shapes, in order to get rid of wrong contacts when backface collision is disabled.
Now it just ignores the generated collision if the contact normal is against the face normal, with a threshold to keep edge contacts.
Added a special case for soft bodies to invert the collision instead of ignoring it, because for now it's the best solution to avoid soft bodies to go through concave shapes (they use small spheres for collision detection). This might be replaced with a better algorithm for soft bodies later (maybe CCD).
Fixes #54208
Additional tests on the following projects:
-MRP from #50218
Previous issue with wrong contacts with backface collision disabled still fixed.
-Test shapes from godotengine/godot-demo-projects#638
No regression spotted.
-Test with soft bodies to make sure they don't go through the ground more easily than before
soft-body-4.0.zip
No regression spotted.
-Backface collision test with multiple shape types
backface-collision-4.0.zip
Bodies go through the top plane (backface disabled) and collide with the bottom plane (backface enabled).