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1 Nov 2024 06:19:50 EDT (-0400)
  Bicubic patches and UV-mapping (Message 1 to 4 of 4)  
From: Gail Shaw
Subject: Bicubic patches and UV-mapping
Date: 23 Aug 2000 10:04:14
Message: <39a3d9de@news.povray.org>
I wonder if anyone can give some advice here...

I've got an union of bicubic patchs exported from moray.
I want to uv-map a texture onto the surface. I added uv-vectors
to the patches, but I'm not sure of the values. values I tried gave
me a very wierd texture, and I'm also not sure what order the patches
are in.

Has anyone else done this? Anyone got some hints? Please??

Thanks

Gail
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From: Libellule
Subject: Re: Bicubic patches and UV-mapping
Date: 23 Aug 2000 14:31:15
Message: <39A418B4.E0125178@insectes.net>
I think the uv points <0,0>, <1,0>, <0,1>, <1,1> will correspond to the
texture's "corners" (easier to think of in terms of an image_map) and
each patch should have a subset of that. eg:

say you have 4 patches

A--B--C
|  |  |
D--E--F
|  |  |
G--H--I

where A,B,C, etc represent the corners of the patches
And say you want the image map uniformly mapped onto the four patches,
then for patch GHDE you would need <0,0>,<0.5,0>,<0,0.5>,<0.5,0.5>
similarly HIEF <0.5,0>,<1.0,0>,<0.5,0.5>,<1.0,0.5>
EFBC <0.5,0.5>,<1.0,0.5>,<0.5,1.0>,<1.0,1.0>
DEAB is left as an exercise for the reader :-)
as long as the uv vectors are the same at the boundaries of the patch, it
should be okay (this is all theory, not tested ;)

Do get Mike's patch from the binaries.programming group, it has support
for uv_mapping type 2 bicubic patch, which is easier to use:
type 2 accuracy 0.01
instead of
type 1 flatness 0.01 u_steps 4 v_steps 4
the type 2 patches use less memory and don't suffer from little black
dots on the surface. The patch has a text file explaining the uv_vectors
usage as well.


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From: Mike
Subject: Re: Bicubic patches and UV-mapping
Date: 23 Aug 2000 17:42:11
Message: <39A44526.2C61FAE4@aol.com>
That description is somewhat correct, but don't forget that the
orientation of the patch is important.  What I mean is that the mapping
is tied to the four corners of the patch, so if you flip the patch, the
mapping will be flipped along with it.  I'll be posting a diagram to
binaries.images to show what is going on a little better.

-Mike


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From: Gail Shaw
Subject: Re: Bicubic patches and UV-mapping
Date: 24 Aug 2000 07:06:23
Message: <39a501af@news.povray.org>
Mike <Ama### [at] aolcom> wrote in message news:39A44526.2C61FAE4@aol.com...
> That description is somewhat correct, but don't forget that the
> orientation of the patch is important.  What I mean is that the mapping
> is tied to the four corners of the patch, so if you flip the patch, the
> mapping will be flipped along with it.  I'll be posting a diagram to
> binaries.images to show what is going on a little better.
>


Thanks. Much appreciated

Gail


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