Invisible Shadow Caster with shader only

Help
,
1

Godot Version

4.3

Question

Is there a way to make a mesh able to switch between invisible and visible but always casts shadow as if it is always opaque just from the shader script?

I’m aware of GeometryInstance3D:cast_shadow, but I’m trying to make Grid Map usable for my use case. Grid map doesn’t store its mesh as GeometryInstance3D, meaning I don’t have access to that, and I haven’t found a way to manipulate each cell without affecting other cell using the same MeshLibrary item. Hence I’m trying to do it via shader only.

I have found a way to identify which mesh located in which cell using VERTEX variable in vertex function and use that in fragment as an indication which grid the current mesh at, but I have not found a way to make it invisible but still cast shadow to other surface.

Thanks in advance!

2 
void fragment() {
	if(! IN_SHADOW_PASS){
		discard;
	}
}
3

IN_SHADOW_PASS isn’t an existing variable, I’m afraid (list of variables). I don’t see any bool that might indicate that the current pass is a shadow pass.

But thank you for responding. Hopefully someone else know.

4

It’s documented in the latest version of the docs:

I think it was added in 4.5, although possibly not documented there. So you might consider upgrading.

I tested it in 4.6 and it’s working even though 4.6 docs still appear to not mention it.

5

You’re right. It is present in 4.5 despite it isn’t listed in the docs. Thank you thank you!!

Upgrading is a big ask in my current state. But it there’s no other way, I would have to. At least now I know it’s possible. I’ll play around with the latest version some more.

I won’t mark it as Solution for now in case someone else know the solution in 4.3. If nothing comes up after a few days, I’ll go with your suggestion. Thanks, once again.

6

On what criteria do you need to switch visibility? Can you describe your specific use case in more detail? There could be a non shader solution.

Also, if you only have a directional light source, it can be determined if you’re in the shadow pass by looking at the projection matrix, assuming your main camera is not orthographic.