cull back face equivalents in shader

[LaidlawFX]

Hey I'm drawing a blank on how to make the side not facing the camera transparent, a simple on and off matte, no ramping. A near equivalent to back face culling, or more like an alternative that keeps the geo there.

[DanBode]

You could take the sign of the dot product between the normal and the I vector. -1 is facing the camera, 1 is facing away.

[anim]

there is isFrontFace VOP which returns 0 for backfacing shading point so just multiply opacity with this value

[LaidlawFX]

cool. I was being a meat Popsicle and it didn't work, works fine now, the dot product, too.

Is there an equivalent in vop sop too so i can use it as an orient vector. I couldn't get the dot product to work, because of the aforementioned meat Popsicle problem. There is no I vector since the vop isn't aware of the camera as I understand, and I don't want the user to have to specify it. Also transforming the p space to the camera space isn't working for I either.

[anim]

you need to specify camera for VOP SOPs if you need to do such things

there is toNDC VOP to transform point to normalized camera space, but you need to specify it, if not user then maybe you can find some clever way with Python, for example with a Button Press it will find camera of the current viewport or something

you can also get transform matrix of the viewport in Python

http://www.sidefx.com/docs/houdini11.0/hom/hou/GeometryViewport#viewTransform

so maybe Python SOP can help you if speed is not the priority

or just use Python to pass that transform to VOPs