Fog shader example in the Built-In Render Pipeline

Shader "Custom/TextureCoordinates/Fog" {    SubShader {        Pass {            HLSLPROGRAM            #pragma vertex vert            #pragma fragment frag						//Needed for fog variation to be compiled.			#pragma multi_compile_fog            #include "UnityCG.cginc"            struct vertexInput {                float4 vertex : POSITION;                float4 texcoord0 : TEXCOORD0;            };            struct fragmentInput{                float4 position : SV_POSITION;                float4 texcoord0 : TEXCOORD0;								//Creates a variable that contains fog coordinates. The parameter must be a free TEXCOORD, for example 1 if TEXCOORD1 is free.				UNITY_FOG_COORDS(1)            };            fragmentInput vert(vertexInput i){                fragmentInput o;                o.position = UnityObjectToClipPos(i.vertex);                o.texcoord0 = i.texcoord0;								//Compute fog amount from clip space position.				UNITY_TRANSFER_FOG(o,o.position);                return o;            }            fixed4 frag(fragmentInput i) : SV_Target {                fixed4 color = fixed4(i.texcoord0.xy,0,0);								//Apply fog (additive pass are automatically handled)                UNITY_APPLY_FOG(i.fogCoord, color); 								//to handle custom fog color another option would have been 				//#ifdef UNITY_PASS_FORWARDADD				//	UNITY_APPLY_FOG_COLOR(i.fogCoord, color, float4(0,0,0,0));				//#else				//	fixed4 myCustomColor = fixed4(0,0,1,0);				//	UNITY_APPLY_FOG_COLOR(i.fogCoord, color, myCustomColor);				//#endif				                return color;            }            ENDHLSL        }    }}