Dissolve Shader

Shader "Cg shader using discard" {
Properties {
         _MainTex ("Texture", 2D) = "white" {}
         _TargetTex("Texture", 2D) = "white" {}


   }
   SubShader {
      Pass {
        // Cull Off // turn off triangle culling, alternatives are:
         // Cull Back (or nothing): cull only back faces
         // Cull Front : cull only front faces

         CGPROGRAM

         #pragma vertex vert
         #pragma fragment frag

        // uniform float _DistanceNear;
         uniform texture2D _MainTex;
         uniform texture2D _TargetTex;


         struct vertexInput {
            float4 vertex : POSITION;
            float2 uv_Maintex:TEXCOORD0 ;
            float2 uv_TargetTex: TEXCOORD1;;
         };
         struct vertexOutput {
            float4 pos : SV_POSITION;
            half4 maintex_alpha : TEXCOORD0;
            half4 targettex_alpha : TEXCOORD1;
         };

         vertexOutput vert(vertexInput input)
         {
            vertexOutput output;

            output.pos =  mul(UNITY_MATRIX_MVP, input.vertex);
            //output.posInObjectCoords = input.vertex;
            //output.

            return output;
         }

         float4 frag(vertexOutput input) : COLOR
         {

            float2 uv_Maintex;
            float2 uv_TargetTex;

            input.maintex_alpha = tex2D (sampler2D, IN.uv_MainTex );
            //maintex_alpha = tex2D (_MainTex, IN.uv_MainTex);
            input.targettex_alpha = tex2D (sampler2D, IN.uv_TargetTex );

            if (maintex_alpha.a < 0.2)
            {
               targettex_alpha.a = 0;
            }
            return targettex_alpha;
         }

         ENDCG
      }
   }
}