[Sidefx-houdini-list] About sprite shader for particle

François Duchesneau sidefx at trinix.ca
Sun May 23 11:12:05 EDT 2010


If you want to create a custom vm_geo_sprite procedural you will have to 
do it with the HDK but it already flexible in the sense that you can any 
custom attribute and tell the vm_geo_sprite you want to recognize. This 
way you can do whatever you want with it if your surface shader (even 
displacement shader I think) is reading that attribute with a Parameter Vop.

The vm_geo_sprite is just telling Mantra to create a small grid always 
facing the camera for every points it finds and reacting to the 
attributes sprite_shop, sprite_rot, sprite_scale etc. The real shading 
is always inside the surface shader.

François

chuong nguyen vien wrote:
> Hi,
>
> Houdini already has a sprite shader and a sprite sop. In order to get a better understand how it works, I am trying to make a sprite shader from scratch. However, i don't know for sure about the way it really works. The sprite shader in houdini contains two node, one is the surface shader and the other is vm_geo_sprite which i guess is a geometry shader. Here is what i get confused:
>
> -When we assign the sprite shader to a particle, how does it take into account the color of each particle i set with a color node ? What is the relation between them (the color node and the shader) ?
>
> My guess it that, in the vm_geo_sprite node, when we put Cd in the attribute, so the vm_geo_sprite will know about the color of the particle (but internally, how  does it know ? Or exactly can we make a custom vm_geo_sprite node ?).
> Then, the vm_geo_sprite node will override the color of the surface shader. But if works like that, then the surface shader is only used for determine other characteristic of the particle.
>
> I will very appreciate for every hint about it :)
>
> Chuong
>
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