Bezier Curves Instead Of Polygons

bezier patches will never(*) be used, the chief reason being
A/ they dont give as much control to the artists as fixed geometry does
B/ they are a PITA to work with
C/ patches joining with other patches/geometry leads to sparkle t-splits
D/ theyre not a unified solution, some shapes cant be represented by them

(*)outside of certain game type exceptions, but for FPSs etc no (though q3a used them for arches, though were tesselated to triangles before rendering, FWIW u could see gaps where the arches meet the other geometry, search for T splits or something for the reasons behind this )

heres the first time they were exposed with consumer hardware
http://www.opengl.org/registry/specs/NV/evaluators.txt

they were soon dropped by nvidia, of the 100-200 extensions, this is one of the handfall that got dropped + IIRC it was dropped like within a couple of years, thats how bad it was

 

Artists don't have to work directly with bezier surfaces though (as in you can convert polygonal models to bezier surfaces with arbitrary precision).

First order bezier triangle is just a flat triangle, they cannot be less expressive than traditional polygons.

 

Their rational versions can represent spheres if that's what you are getting at.

 

You would have to model with bezier in mind then ,since your mesh will suffer and change a lot in the process.

Another pain is continuty between patches. To keepsurface continuity ,a Highly detailed patch must propagate it's complexity across low detail parts (same number of control points between a complex surface an a flat one for example)

Plus ,you can't UV bezier surfaces , it's all implicit.

 

The problem is that this assumption is false - complex shapes don't come down to a few control points with any of the polynomial patch variations.

 

Incorrect. Just increase the dimensions of the control points to include U&V as you do with a triangle mesh.

 

I dont'see what you mean by increasing dimension of the control point.
Bezier patch is 0-1 uv from start to end ,and linear across between control points.

If you mean add control point and move it across the surface , then i don't se that being a really serious workaround...
no control point = no Uv

 

Texture UV can be interpolated from control point values, just like XYZW coordinates ... just because you call the bezier parameters U and V doesn't prevent you from using something different for textures

 

isn't it what i said (meant at least) ? Texturing control only at the control point level ?
If not , it's not something that exist in curent 3d packages....

 

ok , but I (+ the majority of ppl) wouldnt say straight off a single triangle is a bezier triangle

 

I know MFA has already answered, but you are confusing the parametrisation of the Bezier curve which we can define to be (S,T), with the texture coordinates, (U,V). I tried to find some pictures or code I did about 10 years ago to demonstrate it but have no idea where they might be.


FWIW exactly the same thing happens with the rendering of triangles where one can iterate across the surface using barycentric coordinates which, in turn, control texture coordinates.

 

Really ,i don't.
I did a lot of nurbs modeling and shading , but texturing nurbs like you would do with polygons (at least in current 3d apps) is really not possible.You have so few option(plus a projection node that need to be moved along with the geometry).it's just 50 times less flexible .

 

didnt messiah by shiny use something similar ?

ps:
http://209.85.229.132/search?q=cach...multiresolution+mesh&cd=4&hl=en&ct=clnk&gl=uk

 

Here are the particulars of Shiny's system:
http://www.gamasutra.com/view/feature/3379/behind_the_scenes_of_messiahs_.php

Duke Nukem Forever was using MRM at one time. That was during the second edition (=2001 trailer) of the game. I have no idea if they abandoned it in the more modern version that we'll never see.

 

thanks for that

ps: if you find messiah buggy (and you will ) run the glide exe (with a voodoo card or a wrapper) its much more stable

 

How is this really any different from texturing control only at vertex level on triangles?

 

Maya doesn't allow that for a start .. ? ,
wouldn't the interpolation be related to surface tesselation ? (linear at zero ,curved at more)

 

A simple example would be, say, a hedgehog (not the blue one, though )

 

Does Maya have subdivision surfaces? It, frankly, all becomes trivial then, IMHO, assuming your control mesh also has texture vals at the control vertices.

Of course, so you simply include the UV coordinates along with XYZ,in the decision as to how much to subdivide.