POM material

[RyanB]

@;320685

Been thinking about technique a bit.

I have been using the code that reads a 2d texture of volume slices and converts it to ‘3d coordinates’ (for the volume raytraced clouds i was doing’). It’s perfectly possible to use that to store a distance field which in a texture that could then be used to raytrace into from a plane that faced the camera (gpu sprite or some kind of ‘imposter like’ card). The distance field can easily be created in houdini. you can pack a 256x256x256 3d voxel grid into a single channel of a 4096 map. or an 128 cubed grid in the same size map but have 32 frames of animation.

To output a float4 you could pack in the pixel depth offset, and for normals, you could use two channels for just normal offsets (since you already have the render plane normal). that leaves you with an extra single channel for outputting whatever you want (singe channel colour mask, or ramp that was stored in the texture).

Brian riffing here. The first thing I would like to experiment with is baking out a distance field of a grass patch from houdini and raytrace that on a little plane on the floor. that way you can have blades of grass that intersect each other.

Yes you could do for sure. At some point you are re-creating lots of code that exists already using the global distance fields, but there is currently no way to raytrace only a single distance field in a material unless you define the distance field yourself (or using the Volumetric Decals which I have now messed with and added some basic shapes and combiner functions for).

FWIW its fairly cheap to compute the normal using gradient lookup at runtime so you don’t necessarily need to prebake the normal for it. You just need to do a lookup with offset X Y and Z, get the difference from the current sample and then normalize the result.

All the ray tracing examples people are posting are really neat. has been a great learning experience for me as well. Seeing the cat scan data is a really cool use of it. I was testing some cloud rendering stuff that is kind of similar (as well as a ray tracer with subsurface and transmission) but its all kind of in limbo right now as my various experiments are left in half completed states.

I am thinking at some point of making kind of an an animated example material that shows how the ray tracing stuff works for people who are still figuring it out.