Shader "Custom/AlwaysVisibleUI"
{
    Properties
    {
        _MainTex("Texture", 2D) = "white" {} // UI的纹理贴图
    }

        SubShader
    {
        Tags { "Queue" = "Overlay" } // 设置UI的渲染队列为 Overlay，使UI始终在其他物体之上
        LOD 1000

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

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

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

            sampler2D _MainTex;

            v2f vert(appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            fixed4 frag(v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);
                return col;
            }
            ENDCG
        }
    }
}