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Physics collision on mobile accuracy

Hello All,

I am having a problem where collisions sometimes do not occur on iOS (iPhone 5s).

Basically, sometimes collisions will just miss. I am using a main player pawn with spherical collision mesh, and a level boundary which is set to 'Use complex collision as simple'. My Meshes are very low poly (~700 tris for the level mesh).

Most of the time collisions occur as expected, but then on occasion (usually when travelling fast or when there is a performance stutter) my player pawn sphere (sphere collision) will glitch through a wall of my 'complex as simple' mesh.

Should I not be using 'Use Complex Collision As Simple'? It would be very easy to duplicate my meshes from Blender and use them as collision meshes, I just assumed that as everything is so low poly it wouldn't invoke a performance hit, but does it cause accuracy to suffer?

Thanks for any help.

Product Version: UE 4.9
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asked Sep 13 '15 at 07:12 PM in Using UE4

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avatar image fortesdev Dec 07 '15 at 08:41 AM

I have the same annoying problem on 4.10. Playing on the computer works fine. Simulating mobile in computer works fine 90% of time. On real iOS device it works fine 20% of time. And I've noticed that some mesh shapes work better than others, and the impulse/speed during collision is relevant, but not always.

I will play with different levels of complexity in Collision Components among other things, and if I cannot solve it I'll do a bug report.

avatar image fortesdev Dec 07 '15 at 07:36 PM

OK, so this is how I managed to "solve" it, in case it is useful for someone in the future. Go to project settings, Physics, and set in Collision the value of "Triangle min area threshold" to zero. Also enable the PCM. Now physics will consume more processing but won't fail so much on mobile.

avatar image CupMcCakers Feb 14 '18 at 11:32 AM

thanks, this is helpful for my project too!

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Have you tried enabling CCD (constant collision detection) I find it helps when moving fast.

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answered Sep 13 '15 at 10:04 PM

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Alan Webster
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avatar image Doug Sep 13 '15 at 10:23 PM

I did initially try this and still saw some misses, but actually after playing around with a few settings (including turning this back on) I haven't seen any more misses. Thanks.

avatar image Imagine-Games Oct 30 '18 at 06:06 PM

turning on just CCD doesnt seem to solve it in my case.. i still occassionally get collision glitches where the player can walk right through enemies, and other times it works fine... but just turning on CCD definitely did not fix it..

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