有没有会shader的大佬，求帮忙

求帮忙看看是什么问题，研究了半天也搞不懂怎么处理这个错误

Shader "Unlit/ImageEffect"
{
Properties
{
_Heat("Heat",Range(0,1)) = 0
}
SubShader
{
Tags { "RenderType"="Opaque" }
LOD 100
Pass
{
CGPROGRAM
#pragma vertex vert
#pragma fragment frag
#include "UnityCG.cginc"
struct appdata
{
float4 vertex : POSITION;
};
struct v2f
{
float2 uv : TEXCOORD0;
float4 vertex : SV_POSITION;
};
float _Heat;
v2f vert (appdata v)
{
v2f o;
o.vertex = UnityObjectToClipPos(v.vertex);
return o;
}
fixed4 frag (v2f i) : SV_Target
{
fixed v = lerp(1,0,_Heat);
return fixed4(v,0,0,1);
}
ENDCG
}
}
}