uv值显示为颜色

UVColor.shader

Shader "My/UVColor"
{
    Properties
    {
    }

    SubShader
    {
        Tags
        {
            "RenderType" = "Opaque"
        }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma target 2.0

            #include "UnityCG.cginc"

            struct appdata_t
            {
                float4 vertex : POSITION;
                float2 texcoord : TEXCOORD0;
            };

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

            v2f vert(appdata_t v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.vertex.xyzw = o.vertex.xyzw / o.vertex.w;

                o.texcoord = v.texcoord;
                return o;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                fixed4 c = fixed4(0, 0, 0, 1);
                c.xy = i.texcoord;
                return c;
            }

            ENDCG
        }
    }
}