Creating a condition inside stencil block

Graphics Shaders & Materials
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1

I use the following code right now to pass a value into a stencil shader and it works nicely:

Properties{
    [IntRange] _StencilMask("Stencil Mask", Range(0, 255)) = 0
}
SubShader{
    Stencil {
        Ref[_StencilMask]
        Comp always
        Pass replace
    }
}

Now I need to expand my use case. I want to react to the eye (as found in unity_StereoEyeIndex) that is currently being rendered (URP with Single Pass Rendering). I want to set a different stencil value per eye. How would I do that? Is there some sort of “if” condition I can use in the stencil block so that I could declare two properties? I also tried passing a float array but I get an error when writing

Ref[_StencilMasks[unity_StereoEyeIndex]]

Any help would be highly appreciated!

2

You’d probably have to use two passes, and collapse the vertices of one eye so it doesn’t get rendered.

// pseudo code
Pass {
    Stencil {
        Ref[_StencilRefLeft]
        // etc
    }
    
    // vertex shader
        if (unity_StereoEyeIndex != 0) // not left eye
            o.pos = float4(0,0,0,1);
        return o;
    }
    // etc
}
Pass {
    Stencil {
        Ref[_StencilRefRight]
        // etc
    }
   
    // vertex shader
        if (unity_StereoEyeIndex != 1) // not right eye
            o.pos = float4(0,0,0,1);
        return o;
    }
    // etc
1 Like
3

That is a good hint already! In LWRP there is no multi-pass support though. That will probably make this not work. I could assign two materials to the object which would cause unity to iterate twice over the shader. That might do the trick at a bit higher cost. What does o.pos = float4(0,0,0,1); do exactly? Will it tell the shader not to set the stencil there?

4

That tells the

That collapses the vertices of the object to infinity small so it’ll never be rendered for that eye.

1 Like