Flatten every UV? Is it right?

voronov.art

Hello polycounters! My wife is now on her first year studying 3D Environment Art at local university. The teacher says they have to straighten every piece of UV to prevent edge bleeding. Is it the right way? I doubt you can flatten a sphere or something curvy in a flat square without a visible distortion but I may be mistaken.

radiancef0rge

that sounds odd, im not sure why or what the context for a statement like that is.  generally speaking straightening uvs that are clearly straight polygons in the model is a good idea, it sometimes can help with bleeding in mips, it can help with detail normal maps looking correct, but mostly its easier to texture straight things.  i wouldnt say that its necessary to straighten curves that do not have uniform face size.  perhaps others have ideas. 

rollin

This is bit outdated and depends on the case. I am currently doing a MechCommander 2 model an doing a lot of edge straightening. But for current gen stuff I try to find a balance between stretching and straightness. 

Whatsoever: saying you have to always do something is most likely always bullshit

sacboi

Hmm...not sure what her teacher was thinking but really having consistent texel/pixal density is key so planning ahead on choice of texture size would be essential and as for straightening edges, what I've managed to pick up along the way (...not a Texture Painter, here) so, if for example whatever in 3D space happens to have a straight edge then accordingly in UV, straighten as well. To be clear there are no absolutes because exceptions will of course invariably crop up everynow and again. Anyway for further indepth info on the topic I'll invite you to browse this discussion, taking particular note of points raised by @perna...he's a bit of a font of all knowledge, hereabouts

https://polycount.com/discussion/180434/why-do-you-need-to-use-straight-uvs-with-hardsurface-models

poopipe

It's solid advice.

Straight edges will prevent aliasing at seams which is a good way to avoid nasty artefacts - particularly in normal maps, and particularly when texel density is limited (ie, when you're making a game) 

You have to use your iniative  but if you take it as a rule of thumb and only break it when it will cause things to look worse you'll end up with better results.

A good example would be a classic urn or vase. It won't naturally unwrap to a nice straight shape but if you straighten everything so it fits in a neat rectangle you'll get no seam artefacts and you'll be able to lod it better

oglu

If possible we straighten everything. For reasons poopipe mentioned above.