Using stencil buffer to cut out two different planes | Official Unity Discord | Page 1

coarse sphinx Jul 25, 2024, 2:18 PM

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Greetings. I'm a total beginner and need a specific way to cut out some planes of mine. I wanna simulate a very basic and shadow system with two static light sources and parallel shadows. And because you can't have two direct lights that cast shadows, I wanted to do it this way. Its for a quick project, so this should be fine.

In the view we got:

basic plane, which is grey and beneath the other two planes
Some blocks, where either of them has two shadow-planes, where one goes to the top right and one to the top left
red transparent plane, which cuts out the shadow-planes that go to the top right
blue transparent plane, which cuts out the shadow-planes that go to the top left

And with a very basic video about stencil, I was able to create the image attached. But there is a problem with the intersection of the shadow-planes. The intersection of the red and blue shadow should create a grey spot, because the red and blue light source are both blocked.

I tried to solve it myself, but to be honest, I still have problems understanding the stencil and shaders options.

Before I invest so much time, I wanted to ask if this is possible with the stencil shader at all, how would I do it if its possible or if there is an easier way to do this?

I use the 3D URP Render pipeline

blissful falcon Jul 25, 2024, 2:41 PM

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coarse sphinx Greetings. I'm a total beginner and need a specific way to cut out some planes o...

make the blue things check for the value of red (2) or more, on pass write grey (3) on fail write blue (1)

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assuming neutral/default stencil is (0)

coarse sphinx Jul 25, 2024, 2:55 PM

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@blissful falcon
I'm actually having a problem to understand where I would put this in or how it would look syntactically. Currently I only wrote one basic shaders. Would I write that inside of that shader or do I need multiple ones for each color? Does the neutral one need a stencil at all, because it should remain intact?

I'm so confused on how this works, even though I watched multiple videos qwq

Blend Zero One
ZWrite Off

Stencil 
{
  Ref [_ID]
  Comp Always
  Pass Replace
}

blissful falcon Jul 25, 2024, 3:10 PM

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how do u currently draw the shadows

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the geometry itself

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@coarse sphinx

coarse sphinx Jul 25, 2024, 3:49 PM

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@blissful falcon sorry for the delayed response. So my shadows are just Quads that are placed on the same Y-axis as the three planes

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Those shadows have the material of the shader. Blue ones got a stencil ID of 1 and red ones 2.

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The two planes are on their own layers, red and blue, and I render them in the renderer myself

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And the problem seem to be in the "Blue Shadows" settings, because when I only have the red shadows on, it looks correct. But when I only activate the blue one, it still has the problem.

blissful falcon Jul 25, 2024, 8:00 PM

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https://docs.unity3d.com/Manual/SL-Stencil.html

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I can't help atm

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sorry

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The key will probably lie with ReadMask and WriteMask

#Using stencil buffer to cut out two different planes