Shadow casting for raymarched volumes?

I have a shader which raymarches at a constant step into a 3D-texture based volume inside the mesh that the shader is applied to. I implemented the shadowing technique here (at the end of the page), but obviously it just creates shadows for the mesh and not the rendered volume.

So ultimately I'd like to make the volume cast shadows on other objects.
How should I approach this?

 

The same way you're doing your raymarching for the main pass. Presumably your raymarching is outputting a depth from the fragment shader. For directional lights and spot lights the depth is the only thing the shadow map depth pass cares about.

 

Thanks for the quick answer. But how do I output the depth from main pass to shadow pass and how do I use it as an input in the shadow pass. Should I go with render textures?

Also is there something I should know about these:

V2F_SHADOW_CASTER
TRANSFER_SHADOW_CASTER_NORMALOFFSET(o)
SHADOW_CASTER_FRAGMENT(i)

 

I got it working with this answer from you. So thank you.

 

I'm currently trying to do exactly what you wanted to (shadow cast from a raymarched volume), but after reading up on shadowcasting, etc, everything is still going over my head relating to how to get the depth values into the shadow caster. I wonder if you could provide a code sample or demonstration of what you managed to get working? It would greatly help with my understanding

 

This might help:
https://link.medium.com/WkNTnCJnufb