# Why does GPU skinning cause mesh spikes?

**URL:** <https://forums.unrealengine.com/t/why-does-gpu-skinning-cause-mesh-spikes/442904>\
**Category:** Character & Animation\
**Tags:** persona, unreal-engine, editor, question\
**Created:** [February 7, 2019, 2:46pm UTC](https://forums.unrealengine.com/t/why-does-gpu-skinning-cause-mesh-spikes/442904 "2019-02-07T14:46:38Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![TritonSailor](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@TritonSailor](https://forums.unrealengine.com/u/TritonSailor)\
**Post date:** [February 7, 2019, 2:46pm UTC](https://forums.unrealengine.com/t/why-does-gpu-skinning-cause-mesh-spikes/442904/1 "2019-02-07T14:46:38Z")

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I’m getting some severe mesh spikes that go away when I check the CPU skinning box in the Character-\>Advanced tab. That is the only difference between the two attached images.

What is happening? I checked the weight painting and it looks ok to me. I tried moving the mesh via the root bone in blender to check for unweighted vertices, but I didn’t see any tearing occur.

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**Author:** ![smaraux](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@smaraux](https://forums.unrealengine.com/u/smaraux)\
**Post date:** [October 29, 2019, 4:11pm UTC](https://forums.unrealengine.com/t/why-does-gpu-skinning-cause-mesh-spikes/442904/2 "2019-10-29T16:11:50Z")

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Heading there, a bit late, just a guess :  
GPU probably clamp max skinning weight count of each vertex to 4, 8 or such a static value. If your skinning setup has more than that, it will probably be clamped (and maybe not renormalized), leading to unnormalized vertices which would lead to spikes / holes