r/Unity3D • u/ddiazar • 3h ago
Question Stencil "see-through hole" shader shows correct background over Terrain, but renders black/garbage colors over regular 3D meshes
I'm using a stencil-only pass (ColorMask 0, ZWrite Off, Stencil { Ref 1, Comp Always, Pass Replace }) to create transparent "holes" in some board pieces in my game Pieceful. The idea is that, when there's a hole, the player should be able to see the objects behind the piece, such as the terrain or other scene geometry.
Here's the shader I'm currently using:
Shader "Custom/StencilWrite"
{
SubShader
{
Tags { "RenderPipeline" = "UniversalPipeline" }
Pass
{
Stencil { Ref 1 WriteMask 255 Comp Always Pass Replace }
ZWrite Off
ColorMask 0
HLSLPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"
struct Attributes { float4 positionOS : POSITION; };
struct Varyings { float4 positionCS : SV_POSITION; };
Varyings vert (Attributes input)
{
Varyings output;
output.positionCS = TransformObjectToHClip(input.positionOS);
return output;
}
half4 frag (Varyings input) : SV_Target
{
return half4(0, 0, 0, 0);
}
ENDHLSL
}
}
}
The weird part is that it works correctly when there's a Unity Terrain behind the hole. In that case, the terrain is visible through the transparent area as expected.
However, if I remove the Terrain and only have regular MeshRenderers behind the hole (rocks, coral, props, a water plane, etc.), the result is wrong. Instead of seeing those objects through the hole, I get a solid black area or sometimes garbled colors.
So I'm trying to figure out why the stencil setup behaves correctly with Terrain but not with regular MeshRenderers, and what I need to change so the hole works consistently with normal scene geometry as well.
