TEXCOORD0.zで2値化するParticleSystem用シェーダー。 Unity2017.4.24f1で動作確認済み

Particle-AlphaBlended-Clamp.shader

Shader "Custom/Particles/Alpha Blended - Clamp(TEXCOORD0.z)" {
	Properties{
		_MainTex("Grayscale Texture", 2D) = "white" {}
	}

	Category{
		Tags { "Queue" = "Transparent" "IgnoreProjector" = "True" "RenderType" = "Transparent" "PreviewType" = "Plane" }
		Blend SrcAlpha OneMinusSrcAlpha // Alpha Blended
		ColorMask RGB
		Cull Off Lighting Off ZWrite Off

		SubShader {
			Pass {

				CGPROGRAM
				#pragma vertex vert
				#pragma fragment frag
				#pragma target 2.0
				#pragma multi_compile_particles
				#pragma multi_compile_fog

				#include "UnityCG.cginc"

				sampler2D _MainTex;
				fixed4 _TintColor;

				struct appdata_t {
					float4 vertex : POSITION;
					fixed4 color : COLOR;
					float4 texcoord : TEXCOORD0;
					UNITY_VERTEX_INPUT_INSTANCE_ID
				};

				struct v2f {
					float4 vertex : SV_POSITION;
					fixed4 color : COLOR;
					float2 texcoord : TEXCOORD0;
					float2 texcoord2 : TEXCOORD1;
					UNITY_FOG_COORDS(1)
					UNITY_VERTEX_OUTPUT_STEREO
				};

				float4 _MainTex_ST;

				v2f vert(appdata_t v)
				{
					v2f o;
					UNITY_SETUP_INSTANCE_ID(v);
					UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(o);
					o.vertex = UnityObjectToClipPos(v.vertex);
					o.color = v.color;
					o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
					o.texcoord2.xy = v.texcoord.zw; // Copy TEXCOORD0.zw
					UNITY_TRANSFER_FOG(o,o.vertex);
					return o;
				}

				fixed4 frag(v2f i) : SV_Target
				{
					fixed4 texColor = i.color * tex2D(_MainTex, i.texcoord);
					fixed4 col = i.color * step(i.texcoord2.x, texColor.r);
					col.rgb *= col.a;
					UNITY_APPLY_FOG_COLOR(i.fogCoord, col, fixed4(0,0,0,0)); // fog towards black due to our blend mode
					return col;
				}
				ENDCG
			}
		}
	}
}