Opaque ("overwrite") Projector Shader for Decal Projection

Questions & Answers
1

I have been attempting to make a simple “overwrite” version of Unity’s projector shader. I can either respect the color, or respect the transparency, but not both.

I have simplified the frag method to simply take cookie (the texture of the projection) and color tint, skipping all the fall off and fog stuff for now. I hope to eventually add those back in once I figure out what’s going wrong.

Shader "Projector/Overwrite" {
	Properties {
		_Color ("Main Color", Color) = (1,1,1,1)
		_ShadowTex ("Cookie", 2D) = "" {}
		_FalloffTex ("FallOff", 2D) = "" {}
	}
	
	Subshader {
		Tags {"Queue"="Transparent"}
		Pass {
			ZWrite Off
			ColorMask RGB
			Blend DstColor DstAlpha
			//Blend DstColor Zero
			Offset -1, -1
	
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma multi_compile_fog
			#include "UnityCG.cginc"
			
			struct v2f {
				float4 uvShadow : TEXCOORD0;
				float4 uvFalloff : TEXCOORD1;
				UNITY_FOG_COORDS(2)
				float4 pos : SV_POSITION;
			};
			
			float4x4 unity_Projector;
			float4x4 unity_ProjectorClip;
			
			v2f vert (float4 vertex : POSITION)
			{
				v2f o;
				o.pos = UnityObjectToClipPos(vertex);
				o.uvShadow = mul (unity_Projector, vertex);
				o.uvFalloff = mul (unity_ProjectorClip, vertex);
				UNITY_TRANSFER_FOG(o,o.pos);
				return o;
			}
			
			fixed4 _Color;
			sampler2D _ShadowTex;
			sampler2D _FalloffTex;
			
			fixed4 frag (v2f i) : SV_Target
			{
				fixed4 texS = tex2Dproj (_ShadowTex, UNITY_PROJ_COORD(i.uvShadow));
				texS.rgb *= _Color.rgb;
				//texS.a = 1.0 - texS.a;
				return texS;

				/*texS.rgb *= _Color.rgb;
				texS.a = 1.0-texS.a;
	
				fixed4 texF = tex2Dproj (_FalloffTex, UNITY_PROJ_COORD(i.uvFalloff));
				fixed4 res = texS * texF.a;

				UNITY_APPLY_FOG_COLOR(i.fogCoord, res, fixed4(0,0,0,0));
				return res;*/
			}
			ENDCG
		}
	}
}

I am fairly certain the issue lies in the BLEND options. I can either respect the texture * color, or respect the alpha of the texture, but not both together.

Alpha is respected, but the color is no longer accurate

Alpha is ignored, but the color is accurate.

Thanks for your guidance.

2

@DrZoop

    Shader "Projector/Opaque" {
	Properties {
		_Color("Main Color", Color) = (1,1,1,1)
		_ShadowTex ("Cookie", 2D) = "gray" {}
		_FalloffTex ("FallOff", 2D) = "white" {}
	}
	Subshader {
		Tags {"Queue"="Transparent"}
		Pass {
			ZWrite Off
			ColorMask RGB
			Blend One OneMinusSrcAlpha
			Offset -1, -1

			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma multi_compile_fog
			#include "UnityCG.cginc"
			
			struct v2f {
				float4 uvShadow : TEXCOORD0;
				float4 uvFalloff : TEXCOORD1;
				UNITY_FOG_COORDS(2)
				float4 pos : SV_POSITION;
			};
			
			float4x4 unity_Projector;
			float4x4 unity_ProjectorClip;
			
			v2f vert (float4 vertex : POSITION)
			{
				v2f o;
				o.pos = UnityObjectToClipPos(vertex);
				o.uvShadow = mul (unity_Projector, vertex);
				o.uvFalloff = mul (unity_ProjectorClip, vertex);
				UNITY_TRANSFER_FOG(o,o.pos);
				return o;
			}
			
			fixed4 _Color;
			sampler2D _ShadowTex;
			sampler2D _FalloffTex;
			
			fixed4 frag (v2f i) : SV_Target
			{
				fixed4 texS = tex2Dproj (_ShadowTex, UNITY_PROJ_COORD(i.uvShadow));
				texS.rgb *= _Color.rgb;
				texS.a = 1.0-texS.a;

				fixed4 texF = tex2Dproj (_FalloffTex, UNITY_PROJ_COORD(i.uvFalloff));
				fixed4 res = lerp(fixed4(1,1,1,0), texS, texF.a);

				UNITY_APPLY_FOG_COLOR(i.fogCoord, res, fixed4(1,1,1,1));
				return res;
			}
			ENDCG
		}
	}
}

This is the closest I am to an opaque version of the shader. Still has the same problems that you’re having but it’s good enough for something simple like RTS unit selecting.

Transparency is Opaque Black.
The rest of the image to be drawn should have it’s color and alpha channel set to zero (Transparent)