Hi all,

Having trouble accessing in SOP Geometry, attributes, eg(Cd) created in VOP Shader. Is it possible to do this? Had thought it possible based on info from help docs.

Excerpt from help docs - http://www.sidefx.com/docs/houdini11.0/vex/sopnodes [sidefx.com]

“To add an attribute to the geometry…

In VOPs use a Parameter node and set Export to Always or When input is connected.”

Tried this approach, would expect to see point colour attributes in geometry, via material SOP node which applies the VOP Shader.

To give some context to what I'd like to achieve, trying to create particles which are emitted based on a VOP Shader, eg. Black & white noise mapped onto Sphere - Particles emit more from white & less from black areas. Tried using VOP SOP approach, but can't utilise UV mapping(Maybe there is a way?).

Any help would be great.

Cheers
Nick

Your current setup won't really work, as Cd isn't computed until render time. (Mantra doesn't process shaders until you render.) You would have to save out Cd, and bring it back into Houdini with this approach. (look into pointcloud techniques)

You can do what you're trying to do in a VOP SOP though. To access UV attributes, you can take the X and Z axes from P. The downside is that you'll need to increase the resolution of your geometry a lot to get a smooth result.

Here's some good info on pointclouds [sidefx.com].

HTH,
Alan

Here's the vopsop workflow

For uv mapping I temporarily put $MAPU and $MAPV into the point color to use in vopsop. You could just make a parameter in vops (of type vector) called “uv” and access the uv coordinates like that.