【Unity】テクスチャトランジション（グレイスケールからカラー。もしくはその逆）【Shader】

TransitionGrayScaleToColor.shader

Shader "Unlit/TransitionGrayScaleToColor"
{
	Properties
	{
		_MainTex ("MainTexture", 2D) = "white" {}
		_Pattern("Pattern",2D)="white"{}
		_Threshold("Threshold",Range(0.0,1.0))=0.5			      
	}
	SubShader
	{
		Tags { "RenderType"="Opaque" }
		LOD 100

		Pass
		{
			CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			
			#include "UnityCG.cginc"

			struct appdata
			{
				float4 vertex : POSITION;
				float2 uv : TEXCOORD0;                
			};

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

			sampler2D _MainTex;
			sampler2D _Pattern;         
			float _Threshold;			
         
			v2f vert (appdata v)
			{
				v2f o;
				o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv=v.uv;	  	
				return o;
			}
			
			float getgray(fixed4 c)
            		{
                		return c.r*0.2126+c.g*0.7152+c.b*0.0722;
            		} 
			            
			fixed4 frag (v2f i) : SV_Target
			{
				fixed4 col = tex2D(_MainTex, i.uv); 
				float g = getgray(col);
				
				fixed4 gray = fixed4(g, g, g, col.a);
				
				fixed4 pattern = tex2D(_Pattern, i.uv); 
				float pg = getgray(pattern);
				pg = clamp(pg, 0.01, 0.99);
				
				float a = step(pg, _Threshold); 				
				return lerp(gray, col, a);           
			}
			ENDCG
		}
	}
}