Cut geometry based on light

[MortenBøhne]

I'm trying to create a tool that cuts out shadows on a mesh, and transforms the uv's of the shadow-part. The setup only needs to work with one directional light, and only needs to divide into light/dark (no soft shadow or bands)
Our artists usually work in maya, but I figured houdini would be perfect for this task, and a good excuse to introduce houdini engine to the studio.

My approach so far has been to create a grid and orient it with the light, and use a ray-node to project it to the target-geometry, transfer a color attribute, and then cut based on color value. I've added an attributeblur to give the artist a bit of control over the cut.

From here I need to find a way of controlling the grid (orientation based on light, position based on target-geometry, size based on target geometry), to ensure the rays are casts onto the entire target geometry

How can i control the grids position and orientation based on nodes outside the subnet (tagert-geometry, light-direction)?

 

I'm also looking to find a way to control the detail of the cuts. Currently I'm limited by the resolution of the target geometry, but i would like a way to allow the artist to control the amount of detail on the cut

I'm thinking this could be achieved by subdividing the target geometry, but from there i need to find a way of transferring the subdivided cuts to the original mesh

 

I'm still new to houdini, so any help on how to solve those two steps -or if there is a smarter approach for creating the tool altogether, would be greatly appreciated

 

shadow_cut.hipnc

[konstantin magnus]

Hi Morten,

here is a simplification. The ray node alone can do the shadow calculation in this case.

ray_shadow.hipnc

[MortenBøhne]

Thanks, that sure simplifies it a lot!

Any idea how I can transfer the cuts made on the subdivided geometry onto the original geo?

Right now i'm generating curves from the cut-edges and using that to polySplit the original geo, but I have a feeling that could be done a lot simpler too

[MortenBøhne]

I'm trying to keep the original topology for the non-cut primitives by deleting non-original points that are not part of the cuts. Sadly this approach only work at subdivision depth=1, but as soon as I increase the depth, this approach is giving me problems:

Not sure if this is a dead-end if i want to control the subdivision depth further but still keep the topology of my original object

 

 

 

shadow_cut.hipnc