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GPU Skinning

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Multi-joint model limitations

When you import a model with many bones/joints, you might be running across a warning message that looks something like this:

[+ Warning] {Rendering} Detected 75 skeleton joints for subset 0 of mesh 'character', skinning will be performed on the CPU

Do not ignore this information, as it gives you an important hint on how your model will perform in your game. CPU-only skinning is always slower than GPU-accelerated skinning. In order to take full advantage of GPU skinning, your model must not exceed a certain number of joints per subset.

Hardware Limits

Mobiles and Flash

If your joint count (per subset) is > 18:

If your joint count (per subset) is <= 18 and you are using OpenGLES 2.0 on Android, iOS, BlackBerry, Marmalade, or webOS:

18 is also the limit for Adobe Flash.

Consoles

On consoles (XBox 360/PS3), the joint limit for GPU-accelerated skinning is 60 instead of 18.

Desktops

On desktop PCs (OpenGL and DX11), the joint limit for GPU-accelerated skinning is 64.

64 is also the limit on Windows Phone 7 and 8.

Recommendation

If your models exceed the joint limit, It is better to split the skinned geometry into segments to stay under the limit. It is not required to keep the total number of joints of the entire model below the limit. A Character model for instance can be split into legs - torso - arms - head. Keep the joint count under the limit per segment to get the x2/x4 speed gain.

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