RenderMan & RISpec, help-more shaders on the same object

comp.graphics.rendering.renderman - RenderMan interface & shading language.


RenderMan & RISpec >> help-more shaders on the same object

by Manuel » Tue, 01 Nov 2005 20:00:35 GMT

Hi,
english is not my navite language, so please, excuse me for
grammatical errors and poor phrases.

I'm working on a opensource sw that make 3d humans, and export them in
various formats. The rendering is done by AQSIS or PIXIE (or other
renderman compliant).

These are some (old)
screenshot of next version we are developing (not out yet):

http://www.dedalo-3d.com/index.php?filename=SXCOL/makehuman/screenshots.php

I've tried some experiments with renderman engines modifying the famous
Pharr skin shader:

http://www.dedalo-3d.com/index.php?filename=SXCOL/docs/archive/05-05-15_ss_scattering_renderman.html

As you seen in the last image in the page above, when I use the shader,
it, of course, is applyed on all mesh, so the model has skin eyelashes,
skin eyes, skin teeth, skin nails, skin tongue etc...

A way to fix this is export the mesh as differents pieces, and assign a
different shader to each piece. But I think this is a brutal way, and
probably renderman language has a better method to assign different
shaders to same object.

The same problem is, in example, to use UVmaps. I like to use two
different resolutions, in istance 2000 x 2000 px for face texture and
2000 x 2000 px texture for the rest of body.
In this case I must split the original mesh in two parts too? Surely
there is a better way that I don't know...

Besides, splitting the mesh in two parts, and applying the subsurface, I
think will be some problems in joint zones...

Again, sorry for my poor english.

thanks,

Manuel


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RenderMan & RISpec >> help-more shaders on the same object

by Paul Gregory » Thu, 10 Nov 2005 00:12:45 GMT


Manuel,

There is no way to assign multiple surface shaders to a single
primitive in RenderMan.

You have two ways of doing this, firstly, you can do as you suggest and
split the mesh into multiple meshes.

The alternative involves using custom "primitive variables". You can
assign custom values to a primitive and the shader can query them. So
you could attach a new "primitive variable" to the mesh, make it
"uniform" which means each face will have a value, then for each face,
assign an id. In the shader, you would check the id value and shade
accordingly, i.e. one id for eyebrows, one for skin, one for nails etc.


A simple example...

--------------------------------
RIB:

version 3.03

Display "test.tif" "file" "rgba"
Format 200 150 1
Projection "perspective" "fov" 50
Translate 0 0 5

WorldBegin
AttributeBegin
Surface "skin"
PointsPolygons [3 3] [0 1 2 0 2 3]
"P" [
0 0 0
0 2 0
1 2 0
1 0 0
]
"uniform float skinID" [
1
2
]
AttributeEnd
WorldEnd

--------------------------------
SL:

surface skin (uniform float skinID=0)
{
printf("%f\n", skinID);
if(skinID == 1)
{
// Do skin
}
else if(skinID == 2)
{
// Do eyebrows
}
}

--------------------------------


Hope this helps. (Note: I've only tried this with Aqsis)

Paul Gregory
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