UDIM tiles?

Olli.

with the addition of this feature in Substance i became curious as to what UDIM actually is.

After reading a few articles on it ive so far figured it seems like its just a way of having multiple UV sets on a single UV channel.

Im still quite confused as to what purpose this is?

First of all, if the idea is you can map an object on to multiple UV tiles in the same channel, why not just scale them to uv 0-1 and use a single texture for it all?

another thing thats confusing to me is the fact that UDIM is restricted to 10 lateral tiles, after which it jumps to the next row. So if you for example had 2000 UDIM tiles, the overall texture space would be very tall and very thin, 200x10. Wouldnt it be difficult to map certain objects to such an oddly shaped texture space?

Burpee

You can have for exemple 10x4k map on one single mesh, let's take a body, you can't put his head on a single 4k tile ( 0-1 ), his left arm on another one ( 0-2 ) his body on the third one ( 0-3 ) etc.. so you'll have far more resolution than one single map. ( and you can't use 16k + map in a render engine )

And some render engine rather have a lots of little node file to read than one really big, for exemple if you have 16 x 1k map with Arnold, he'll only use those he need on the shot, but if you have 1 16k map ( for the exemple ), he'll have to fully load it,

It's restricted to 10 U but nearly infinite V, once you reached 1009, you can go for 1010, 1020, 1030 etc...

Olli.

is it possible to have a mesh mapped to more than one tile?

like if my bodys head was really big, could I have it span across tiles 1001 to 1002 or would I get a seam?

Also how would you go about texturing something like this? Or is stuff like this usually just sculpted and polypainted and then baked automatically in to UDIM tiles?

thomasp

the limit of 10 tiles horizontally is apparently artificial and related to file sorting and the way things are expected to work at the place where it was developed (weta).

you'd use a 3d texture painter to handle these tiles. mari or mudbox would seem the obvious candidates.

throttlekitty

It's more of a notation system for behind the scenes stuff, and makes working with multitextured objects easier; it's the whole point! Otherwise, it's the same as offsetting your UV tiles and assigning textures manually. Your character could have a map for arms, torso, head and legs if you wanted. Or 6 maps for each face on a cube; without UDIM, you'd have to create and assign a material/texture to each face.

I think you'd be safe to span tiles, there's a chance you could get a filtering seam at the border of the textures.

Technique depends on what you're making, but UDIM doesn't change the workflow here. If I had some hard surface model with a ton of parts across 5 maps, I'd probably be using Quixel or Substance, and any 3d painting for character or organic stuff.

MagicSugar

Olli. said:First of all, if the idea is you can map an object on to multiple UV tiles in the same channel, why not just scale them to uv 0-1 and use a single texture for it all?

With udim you can, generally speaking, mix and match uv sets to different texture resolutions.  Instead of one 4k texture crowded and packed by all object uvs you can specify which uvs are maximized on a 4k texture (for example) and which ones are on 512 x 512 (or similar low res).  Keep in mind this was originally designed for film vfx use where, I think, the minimum low-res texture resolution is or was 2K.

Modo's primer is general enough to understand the underlying theory: http://modo.docs.thefoundry.co.uk/modo/801/help/pages/modotoolbox/UDIM_Workflow.html  

If you want to see what multi udims (aka "patches") look like on a model, The Foundry has sample assets available for free download under it's "learn mari" page (but I'm not sure if Substance can open them with no errors).

MagicSugar

Olli. said:

Also how would you go about texturing something like this? 

In Mari you can paint or project paint textures in udim view as well as in full object perspective, ortho, or split (half uv/udim view half perspective).

Udims/patches are also used as quick auto selection sets to hide/unhide or mask.

Froyok

Reading recommendation.
https://www.fxguide.com/featured/udim-uv-mapping/

musashidan

Udims were developed out of necessity for texturing vfx assets. These days it isn't unusual for a hero asset to have 50-100 x8 or 16k maps. The memory overheads are obviously massive for this but it doesn't really matter for offline rendering.

RobertT

UDIM seems like a concept that would pre-date the advent of support for multiple materials per object in 3D modelling. However, it does not pre-date that support.  It seems to have no benefit. It just creates more obscure texture names.   Almost every graphics shader repeats the texture both horizontally and vertically, so you could put the UVs in different sections per material anyways.  You do not need UDIMs to go above 1 in UV space.  Neither Unreal Engine 4 nor Unity 2018 by default support UDIMs, so you would either need to use multiple materials (more draw calls), or atlas the materials (in watch you'd consume more memory).

CreativeSheep

@RobertT You're not confusing with U-repeat and V-repeat options in most shaders ?

Burpee

RobertT said:

UDIM seems like a concept that would pre-date the advent of support for multiple materials per object in 3D modelling. However, it does not pre-date that support.  It seems to have no benefit. It just creates more obscure texture names.   Almost every graphics shader repeats the texture both horizontally and vertically, so you could put the UVs in different sections per material anyways.  You do not need UDIMs to go above 1 in UV space.  Neither Unreal Engine 4 nor Unity 2018 by default support UDIMs, so you would either need to use multiple materials (more draw calls), or atlas the materials (in watch you'd consume more memory).

Udim are quite essential, if you want to have loads of resolution on a single mesh you can't just have 1 tile with a 100k map, ( actually you can't go over 16k anyway ) 
You're mixing its use in game asset and film/vfx asset

edit : woh june 2016... al'right then