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Re: Texture - Object association under subdivision

Posted by ati3414 on January 26, 2005 at 11:19:07:

In Reply to: Re: Texture - Object association under subdivision posted by Scott Schaefer on January 26, 2005 at 10:36:25:

: : I have read a lot of papers before asking this question : I cannot find any reference as to how one generates the texture coordinates for a subdivision surface. Case and point: I am trying to to subdivide a surface in real time
: : (adaptively with respect to the distance between the object and the viewer). I think I got a fairly good idea how to produce a good termination criterion. The thing is: how can I generate the association between the texture space and the object space? How do I get the (u,v) texture pair for each vertex generated by subdivision? Most of the objects shown in the current papers are untextured.....

: Subdivision is a parametric process. This means that you can associate any values that you want with the vertices and they may be subdivided as well. So one technique is to not only subdivide the geometric positions of the vertices but their texture coordinates as well. Editing such texture coordinates may be somewhat difficult though because the values you assign to the base mesh do not necessarily coincide with the values after subdivision. (There are ways around this problem using the limit masks associated with the subdivision scheme though.)

: Another possibility is simply to associate some texture function like cylinderical projection with the object and automatically generate texture coordinates for the mesh. This process is not very desirable though because the artist has little to no control over how the object is textured.

Me in particular? No. My programs allow me to control the level of subdivision because I mainly use them for generating figures for papers. However, that's a decent criteria. Notice that, for real-time applications, this level of detail may not be possible. Subdivision is inherently an exponential process and can be quite expensive as the level of subdivision increases.

Scott,

I am trying to see if I can implement Real Time (sorry for shouting) surface subdivision. I managed to do this very well for parametric surfaces (Bezier, Splines, Nurbs). From the answers above I am starting to get the sense that this may be much more difficult in the case of subdivision surfaces since :
1. I need a "human eye " - independent termination criterion (the algorithm needs to decide when to terminate the subdivision). Preferably the criterion should be distance dependent such that I can generate a continuum of leves of detail

2. I need an automatic way of transferring the geometric subdivision to the attribute coordinate (texture coordinate, for example) subdivision such that the resulting objects look good under animation. Does the "limit masks" method quoted above gurantee correct attribute generation? My gut feel says "no" for the mere reason that the texture coordinates associated with the base mesh cannot be stretched correctly over the subsequent (refined) meshes.

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Re: Texture - Object association under subdivision ati3414 15:18:55 01/26/05 (1)

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: : : I have read a lot of papers before asking this question : I cannot find any reference as to how one generates the texture coordinates for a subdivision surface. Case and point: I am trying to to subdivide a surface in real time : : : (adaptively with respect to the distance between the object and the viewer). I think I got a fairly good idea how to produce a good termination criterion. The thing is: how can I generate the association between the texture space and the object space? How do I get the (u,v) texture pair for each vertex generated by subdivision? Most of the objects shown in the current papers are untextured..... : : Subdivision is a parametric process. This means that you can associate any values that you want with the vertices and they may be subdivided as well. So one technique is to not only subdivide the geometric positions of the vertices but their texture coordinates as well. Editing such texture coordinates may be somewhat difficult though because the values you assign to the base mesh do not necessarily coincide with the values after subdivision. (There are ways around this problem using the limit masks associated with the subdivision scheme though.) : : Another possibility is simply to associate some texture function like cylinderical projection with the object and automatically generate texture coordinates for the mesh. This process is not very desirable though because the artist has little to no control over how the object is textured. : Me in particular? No. My programs allow me to control the level of subdivision because I mainly use them for generating figures for papers. However, that's a decent criteria. Notice that, for real-time applications, this level of detail may not be possible. Subdivision is inherently an exponential process and can be quite expensive as the level of subdivision increases. : : Scott, : I am trying to see if I can implement Real Time (sorry for shouting) surface subdivision. I managed to do this very well for parametric surfaces (Bezier, Splines, Nurbs). From the answers above I am starting to get the sense that this may be much more difficult in the case of subdivision surfaces since : : 1. I need a "human eye " - independent termination criterion (the algorithm needs to decide when to terminate the subdivision). Preferably the criterion should be distance dependent such that I can generate a continuum of leves of detail : 2. I need an automatic way of transferring the geometric subdivision to the attribute coordinate (texture coordinate, for example) subdivision such that the resulting objects look good under animation. Does the "limit masks" method quoted above gurantee correct attribute generation? My gut feel says "no" for the mere reason that the texture coordinates associated with the base mesh cannot be stretched correctly over the subsequent (refined) meshes.

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