StereoScreenCutoutShader.shader

//based on https://github.com/Brackeys/Portal-In-Unity/blob/master/Portal/Assets/ScreenCutoutShader.shader
// Upgrade NOTE: replaced 'mul(UNITY_MATRIX_MVP,*)' with 'UnityObjectToClipPos(*)'

Shader "Unlit/BasicScreenCutoutShader"
{
	Properties
	{
		_MainTex("Texture", 2D) = "white" {}
	    _EyeDistance("Eye Distance", Float) = 0
	}
	SubShader
	{
		Tags{ "Queue" = "Transparent" "IgnoreProjector" = "True" "RenderType" = "Transparent" }
		Lighting Off

        Cull Back

        ZWrite On

        ZTest Less


        Fog{ Mode Off }

		Pass
		{
			CGPROGRAM
#pragma vertex vert
#pragma fragment frag

# include "UnityCG.cginc"

			uniform fixed _EyeDistance;

            struct appdata {
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;
				UNITY_VERTEX_INPUT_INSTANCE_ID //Insert
			};

			struct v2f {
				float2 uv : TEXCOORD0;
				float4 vertex : SV_POSITION;
				float4 screenPos : TEXCOORD1;
				UNITY_VERTEX_OUTPUT_STEREO //Insert
			};

			v2f vert(appdata v) {
				v2f o;
				UNITY_SETUP_INSTANCE_ID(v); //Insert
				UNITY_INITIALIZE_OUTPUT(v2f, o); //Insert
				UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o); //Insert

				o.vertex = UnityObjectToClipPos(v.vertex);
				
				//o.screenPos = ComputeScreenPos(o.vertex);
				o.screenPos = ComputeNonStereoScreenPos(o.vertex);// ComputeScreenPos(o.vertex);
				o.uv = v.uv;
				return o;
			}
			UNITY_DECLARE_SCREENSPACE_TEXTURE(_MainTex);
			//sampler2D _MainTex; 
			half4 _MainTex_ST;

			fixed4 frag(v2f i) : SV_Target
			{
				UNITY_SETUP_STEREO_EYE_INDEX_POST_VERTEX(i); //Insert

				fixed4 col;
#if UNITY_SINGLE_PASS_STEREO
				float2 screenUV = i.screenPos.xy / i.screenPos.w;
				if (unity_StereoEyeIndex == 0) {
					//Use left side of texture, then move to left eye position
					screenUV.x = (screenUV.x)*0.5f
							   - _EyeDistance*0.5f;
					//col = tex2D(_MainTex, UnityStereoScreenSpaceUVAdjust(screenUV, _MainTex_ST));
					col = tex2D(_MainTex, screenUV);
				} else {
					//Use right side of texture, then move to the right eye position
					screenUV.x = ((screenUV.x)*0.5f) + 0.5f 
							   + _EyeDistance*0.5f;
					col = tex2D(_MainTex, screenUV);
					//col = tex2D(_MainTex, UnityStereoScreenSpaceUVAdjust(screenUV, _MainTex_ST));
				}
				
#else
				i.screenPos /= i.screenPos.w;
				col = tex2D(_MainTex, UnityStereoScreenSpaceUVAdjust(i.screenPos, _MainTex_ST));

#endif
				return col;
			}
			ENDCG
		}
	}
}