[Sidefx-houdini-list] modify cd attribute using image sequence.

Stephen Gustafson sgustafso at gmail.com
Fri Feb 2 19:45:42 EST 2007

VEX shaders don't have an understanding of Houdini expressions (and so, no  
$F variables). You can still do this, but you should pipe in the  
expression for your image sequence from a parameter on the VEX shader  
itself, not by embedding it directly into the VEX code.
If you really want to have it so that your expression is embedded (i.e.,  
so that whoever is using the shader doesn't have to set it), you can set  
the default string on this filename parameter to your image sequence  
expression, and then even make the parameter invisible if you want. VEX  
will still complain if you use a default like that, but it'll still work,  
because it's an exported parameter.
The difference is that, when you place your expression on an external  
parameter, Houdini will parse that expression first, and pass along the  
resolved image name into the VEX shader for Mantra to call. Mantra doesn't  
understand expressions (though I'm sure there are ways of getting it to).  
And even if it could, you probably wouldn't want it to: If your expression  
was being evaluated within the shader itself, it would probably end up  
being parsed several hundred thousand times per frame.

So yeah, send the expression in through a parameter node. :)

On Sun, 04 Feb 2007 10:37:28 -0800, andi <claystudio at cbn.net.id> wrote:

> hi all,
> i created a 100x100 grid, then tried to modify the Cd attributes.
> so the plan is i will use an animation (image sequence) as a map to  
> modify the Cd attribute.
> i created a VEX geometry operator and inside this VEX i used a colormap  
> node.
> with this colormap nodes i try to fetch the image seq files, but the  
> problem is this
> colormap node cannot handle image seq (the error message : cannot have  
> channel that depends on time),
> so i cannot use format like : imagename.$F4.jpg.
> so if i want the image sequence is applied to the cd attribute, how to  
> do it?
> thanx. _______________________________________________
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> Sidefx-houdini-list at sidefx.com
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