UV performance cost when packing vs tiling UV islands?

Proponent_

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?



Thanks!

dimwalker

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

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_

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

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,