Working with Ptex

#1

Hey all,

I’ve been wondering lately. Now that software like Mari and Mudbox give you the option to texture using Ptex, and renderers like Vray allows u to use Ptex, what stops me from giving up UV mapping entirely?

Assuming it’s comfortable for me to not be able to use photoshop and I don’t mind doing all my texturing in mudbox/mari, what else is negative about using Ptex right now?

It seems like it’s not very popular and I’m wondering why.

Thanks.

#2

neil did a good job comparing uvs against ptex…
http://www.neilblevins.com/cg_education/ptex/ptex.htm

#3

Thanks, that clears things up.

So basically the tech is progressed enough that all I have to consider when deciding to whether or not use it, is whether or not it’s a preferable system for the specific model?

There are no glitches and stuff to be careful of?

#4

Its not possible to use to Vector displacement with PTex … I gather its not possible to use Tangent Space Normal Maps for the same reason but would be good for someone more experience to confirm.

#5

vector dispmaps are working fine if supported by the renderer…
http://www.youtube.com/watch?v=YNgy2CYEvfI

the main reason for not using ptex is for me that if you change the topology you have to rebake your textures… and thats not always possible… its to risky to loose all your textures…

#6

The original Ptex specification does not explain in any way how vector displacements are treated, and what would the RGB components correspond to - f.e. is the blue component the displacement along the surface normal, or the green one? If one follows the convention from normal maps, it would be the blue one; however from the video it seems that it is the green one. An additional issue is that vector displacements require that the subdivision algorithm in the renderer exactly matches the one used for baking the vector displacements, which is currently not the case (of course, OpenSubdiv will probably help to align this for the future). So we preferred to wait until the dust settles down a bit and this is cleared up before implementing Ptex vector displacements in V-Ray.

Best regards,
Vlado

#7

Same here. For this reason alone I dropped Ptex and went back to UVs once I had to retexture an object 3 times. I also failed to bake Ptex to texture.
If this ever changes I’d love to try it again, but before this happens, it’s pretty much unusable IMO.

#8

Oh! thanks for correcting me :slight_smile: For some reason I thought it was not possible without UV Space in principal. Sorry for giving bad info!

#9

i dont understand the problem here… there shouldnt be a difference between storing the color data into a ptex fila and a texture… the color should be the same… vector dispmaps from mudbox are working with exr files in vray… why shouldnt it work with ptex… (the subd algorithm is a different problem)…

and normalmpas are different in max and maya… there is no standard…

#10

There is no problem to store the data; the problem is to figure out what the data means.

vector dispmaps from mudbox are working with exr files in vray… why shouldnt it work with ptex…
With .exr files, the vector is defined relative to the surface UV coordinates. Since Ptex textures do not use UVs, it is not clear (at least to me) how to convert the color of the vector displacement into actual offsets for the displaced point.

Best regards,
Vlado

#11

thats a good question… but i think the devs should answer if you ask them…https://groups.google.com/forum/?fromgroups#!forum/ptex

#12

vector displacement is simply a direction and a magnitude. As long as your renderer supports object space vector displacement (as opposed to tangent space), you should have no problem with using ptex to create vector displacements. Basically you’re saying, I want the surface to move in some arbitrary vector direction, for some distance. Storing the textures as 32 bit is important for vector displacement.

Ptex is powerful, but it requires a slightly different workflow than what most people are be used to. Topology changes are probably the biggest issue, as you need a method of transferring the texture data. Once 3d painting and texture transfer become more of a household standard, ptex will likely catch on. Neil Blevins sums it up well. Being able to flatten geometry is really useful as well, as you get the best of both worlds

#13

In theory you can use point cloud data to put textures back onto geo that has had its topology changed.

Ptex in Mari has given birth to an awesome spherical projection work flow pioneered by scott metzger. Look up some of his stuff, its incredible. I use Vray to render ptex work. Its good for environment work where you dont want to have to do lots of tedius UV mapping

#14

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