unity fragment shader input

// Upgrade NOTE: replaced '_Object2World' with 'unity_ObjectToWorld'

Shader "Unlit/VerifyGL"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

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

            struct v2f
            {
                float4 vertex : SV_POSITION;
				float4 uv:TEXCOORD0;
				float4 world:TEXCOORD1;
				float4 screen:TEXCOORD2;
            };

            sampler2D _MainTex;
			sampler2D _src;
            float4 _MainTex_ST;
			float4x4 _VP;
			float4 xa;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
				o.uv = v.uv;
				o.world = mul(unity_ObjectToWorld, v.vertex);
				o.screen = ComputeScreenPos(o.vertex);
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
				// 1.使用世界坐标插值
			/*	float4 clipPos = mul(UNITY_MATRIX_VP, i.world);
				float2 uv = clipPos / clipPos.w;
				uv = uv * 0.5 + 0.5;
				float4 col = tex2D(_MainTex, uv);
				return col;*/

				// 2.使用ComputeScreenPos
			/*	float4 col = tex2D(_MainTex, i.screen.xy / i.screen.w);
				return col;*/

				// 3. 使用unity的屏幕空间坐标
				float2 uv;
				uv.x = i.vertex.x / 800;	//800是屏幕宽度
				uv.y = 1-i.vertex.y / 600;	//600是屏幕高度
				float4 col = tex2D(_MainTex, uv);
				return col; 
			}
            ENDCG
        }
    }
}

FIG paste Smectite: