UV performance cost when packing vs tiling UV islands?

Proponent_ · Jun 10 2025

Hi guys, trying to wrap my head around UVs and how they affect performance in-engine. Is the performance cost of the UV map the same whether islands are packed into one tile, or split across adjacent tiles? I am assuming that since there are the same amount of islands in either case, the rendering hit is the same.

For example, do these layouts have the same performance impact?

Image: https://us.v-cdn.net/5021068/uploads/editor/uu/bbnpn7ulots4.png

Thanks!

dimwalker · Jun 11 2025

You can save some memory by using smaller type to store your UV coords when it's packed or at least within 8x8 tiles for example.

Klunk · Jun 11 2025

Back in the day IIRC with what brain cells I have left perhaps ps1 had a uv/tiling limit. in the engine btw every uv seam adds a new vertex (position, normal, tangent, uv1, uv2, binormal, vertex color, vertex weight .... etc etc per vert) for every vert along the seam.

Proponent_ · Jun 11 2025

Thank you guys, was pretty sure I was on the right track but after staring at this stuff for so long I begin to question my own identity

poopipe · Jun 11 2025

Klunk said:

Back in the day IIRC with what brain cells I have left perhaps ps1 had a uv/tiling limit.

it's pretty standard still to have a limit on how far outside 0:1 you can get away with. usually 16 units in either direction

sometimes its a hard engine restriction - others you just get crap results due to floating point error,

UV performance cost when packing vs tiling UV islands?

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