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Question by KHex · Feb 05, 2012 at 07:00 PM · shader

Question about ColorMask

I just wanted to understand how colormask works and in this example, with grabpass.

 Shader "Custom/FadeOut" {
 Properties {
     _MainTex ("Base (RGB)", 2D) = "white" {}
     _Opacity("Opacity", Color) = (0,0,0,0)
     _Alpha2("Alpha Value", Float) = 1
 }
 SubShader {
     Tags { "RenderType"="Transparent" }

     
     Pass {
         ColorMask A
         
         SetTexture [_MainTex]{
             constantColor(1,1,1,[_Alpha2]) 
             combine texture lerp(constant) constant
         }
     }

     GrabPass {}

     Pass{

         Blend SrcAlpha Zero
         SetTexture[_GrabTexture]{ combine texture }     
     }
 } 
 FallBack "Diffuse"

}

In the above, I just am using the default-particle texture on a plane, that's it. What I want to understand here are the results.

In my first pass, I write out to the color buffer only the alpha values and then I use GrabPass to store the rest as a texture. In my viewport, the result is nothing of course, just the default blue render background. However, the texture which is stored, what are the other color values? I understand that my alpha values are different.

I ask because I am confused as to why SrcAlpha Zero works. The GrabTexture technically shouldn't have anything in it. In my mind, I should get all black since the color channels are all 0 so it shouldn't matter what the alpha value is stored.

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