Question by konstantin_lozev · Aug 28, 2018 at 11:23 AM · shader shaders transparency cutout

Simplest Unlit Instanced shader - how to enable switching it on/off (with AlphaTest)?

I have a prototype that uses a simple unlit shader that supports instancing where the color is adjustible per instance:

     Shader "SimplestInstancedShader"
     {
     Properties
     {
         _Color ("Color", Color) = (1, 1, 1, 1)
     }
 
     SubShader
     {
         Tags { "RenderType"="Opaque" }
         LOD 100
 
         Pass
         {
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #pragma multi_compile_instancing
             #include "UnityCG.cginc"
 
             struct appdata
             {
                 float4 vertex : POSITION;
                 UNITY_VERTEX_INPUT_INSTANCE_ID
             };
 
             struct v2f
             {
                 float4 vertex : SV_POSITION;
                 UNITY_VERTEX_INPUT_INSTANCE_ID // necessary only if you want to access instanced properties in fragment Shader.
             };
 
             UNITY_INSTANCING_BUFFER_START(Props)
                 UNITY_DEFINE_INSTANCED_PROP(float4, _Color)
             UNITY_INSTANCING_BUFFER_END(Props)
          
             v2f vert(appdata v)
             {
                 v2f o;
 
                 UNITY_SETUP_INSTANCE_ID(v);
                 UNITY_TRANSFER_INSTANCE_ID(v, o); // necessary only if you want to access instanced properties in the fragment Shader.
 
                 o.vertex = UnityObjectToClipPos(v.vertex);
                 return o;
             }
          
             fixed4 frag(v2f i) : SV_Target
             {
                 UNITY_SETUP_INSTANCE_ID(i); // necessary only if any instanced properties are going to be accessed in the fragment Shader.
                 return UNITY_ACCESS_INSTANCED_PROP(Props, _Color);
             }
             ENDCG
         }
     }
     }

I am able to change the per instance color in code without a problem. However, I want to also be able to make some of the instances disappear in code. The most straightforward and least resource expensive way I found would be to use the AlphaTest Queue and not the Transparent Queue. However, while there are quite a few resources on how to make that with the Transparent Queue (e.g. https://unity3d.com/learn/tutorials/topics/graphics/making-transparent-shader?playlist=17102), I did not find a good explanation of how to do it with the AlphaTest Queue. Based on what I have read I have to change

     Tags { "RenderType"="Opaque" }

     Tags {"Queue"="AlphaTest" "RenderType"="TransparentCutout"}

and I would have to use the clip() function in a way that would return hide the whole object if the alpha is set to 0. I think this could be done by

     clip(_Color.a-0.1))

but this is only a wild guess on my part at that point. I have little idea on whether that would work and how to go on from there, or whether I am missing something. Thanks in advance for the help.

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