Rewrite simple alphamask fixed function shader to surface or cg shader

Questions & Answers
1

Until now I’ve used this shader to dynamically make transparent holes in a texture.

Shader "AlphaMask" {
  Properties {
      _MainTex ("Base (RGB)", 2D) = "white" {}
      _AlphaTex ("Alpha (A)", 2D) = "white" {}
  }
  SubShader {
    Tags { "RenderType" = "Transparent" "Queue" = "Transparent"}
    ZWrite Off
    Blend SrcAlpha OneMinusSrcAlpha
    ColorMask RGB
 
    Pass {
       SetTexture[_MainTex]  { Combine texture }
       SetTexture[_AlphaTex] { Combine previous, texture }
    }
  }
}

_MainTex is a high-resolution texture that’s read-only, while _alphaTex is a low-res
texture that’s frequently updated with SetPixels()/Apply().

After updating from my custom 2D-system where I used texture2D to the new Sprite-class,
the SpriteRenderer won’t accept this shader since it’s fixed function.

I’ve spent time searching for a solution to this, but no luck so far.
Surely there’s some simple way to update this code for surface or cg?

2

So I don’t normally code things for people, on principle, but this seemed like the easiest way to explain it. And it’s mostly copy pasted from unity docs. I just tweaked it to serve your purpose.

(I also didn’t test it so I’ll leave the bugs to you :slight_smile: )

  • I made it a transparent shader by
    placing it in the right queue and
    setting the correct blend mode.

  • I added 2 textures as input.

  • I use the same uvs for both.

  • I read in main tex.

  • Then I read in alphatex and set the
    alpha based on my alphatex’s alpha.

    Shader “Tutorial/Textured Colored” {
    Properties {
    _Color (“Main Color”, Color) = (1,1,1,0.5)
    _MainTex (“Texture”, 2D) = “white” { }
    _AlphaTex (“Texture”, 2D) = “white” { }
    }
    SubShader {

     Tags { "RenderType"="Transparent" "Queue"="Transparent" }
 LOD 200
 Blend SrcAlpha OneMinusSrcAlpha
 ZTest Less

 Pass {

    CGPROGRAM
    #pragma vertex vert
    #pragma fragment frag

    #include “UnityCG.cginc”

    float4 _Color;
    sampler2D _MainTex;
    sampler2D _AlphaTex;

    struct v2f {
    float4 pos : SV_POSITION;
    float2 uv : TEXCOORD0;
    };

    float4 _MainTex_ST;

    v2f vert (appdata_base v)
    {
    v2f o;
    o.pos = mul (UNITY_MATRIX_MVP, v.vertex);
    o.uv = TRANSFORM_TEX (v.texcoord, _MainTex);
    return o;
    }

    half4 frag (v2f i) : COLOR
    {
    half4 texcol = tex2D (_MainTex, i.uv);
    texcol.a = tex2D (_AlphaTex, i.uv).a;
    return texcol * _Color;
    }
    ENDCG

     }

    }
    Fallback “VertexLit”
    }

3

This works for me except for one strange issue. The edges of the sprite are being “repeat stretched”. Have no idea what could be doing this. I do have many sprites near each other.