Access scene from vexdso

[mrice]

I'm trying a scheme where a vex plugin could access nodes in the scene while the shader is evaluating, but I'm getting undefined symbol errors when the shader runs.

My guess is that when the vex is executed we're in a similar context to VRAYProcedural, and disconnected from houdini at that point. Is that right?

Any way this could work?

[edward]

The vex code is compiled using vcc, a process external to Houdini. Then the compiled vex code is evaluated in Mantra at render time. If you want to access nodes, then you probably want to do it as some sort of hscript/python expression code that is on the SHOP parameter so that when Houdini evaluates the shader parameter for output into the IFD file for Mantra, it will be run. You will probably want this to be a hidden parameter.

[mrice]

Thanks Edward,

Well I was thinking of ways it might be possible to render a prepass in mantra, process data from prepass, and then use that in the final render, without having to serialize/unserialize a large data structure in-between. So from a vex-op maybe you could execute the prepass render from the dso's constructor, and use a shared object between the two renders.

But I don't think its doable, and in the grand scheme, maybe writing millions of points to a file isn't a big deal.

[edward]

Well, if you just want to write out points, then there's the point cloud functions you can use. Offhand, I don't think millions of points should be an issue. I've written out 3 GB points using MDD from Houdini ... but then I was on an i7.