UNITY中以Shader的方式实现虚拟围栏

在unity中实现以Shader虚拟围栏，效果是靠近就显示，离开就消失。或者是在VR里实现一个虚拟的安全区。
基于URP渲染管线，这里以十字图案纹理为例。可以自定义显示半径，淡出距离，远近渐变色自定义。

Shader "Custom/VRProximityFadeTexture"
{
    Properties
    {
        [Header(Texture)]
        _MainTex ("十字图案 (透明背景)", 2D) = "white" {}
        _Density ("十字密集度", Float) = 2.0          // 数值越大，十字越多
        _Offset ("纹理偏移 (X,Y)", Vector) = (0,0,0,0)

        [Header(Display Settings)]
        _Radius ("完全显示半径 (m)", Float) = 1.0
        _FadeDistance ("淡出距离 (m)", Float) = 0.5

        [Header(Color Settings)]
        [Toggle] _UseNearFar ("启用双色渐变", Float) = 1
        _MainColor ("单色 (仅单色模式)", Color) = (1, 1, 1, 1)
        _NearColor ("靠近颜色", Color) = (1, 0.8, 0, 1)
        _FarColor ("远处颜色 (渐变终点)", Color) = (0.2, 0.2, 0.2, 0)
    }

    SubShader
    {
        Tags { "RenderType" = "Transparent" "Queue" = "Transparent" "RenderPipeline" = "UniversalPipeline" }
        Pass
        {
            Name "ForwardUnlit"
            Tags { "LightMode" = "UniversalForward" }

            Blend SrcAlpha OneMinusSrcAlpha
            ZWrite Off
            Cull Off

            HLSLPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma multi_compile_instancing

            #include "Packages/com.unity.render-pipelines.universal/ShaderLibrary/Core.hlsl"

            struct Attributes
            {
                float4 positionOS : POSITION;
                float2 uv : TEXCOORD0;
                UNITY_VERTEX_INPUT_INSTANCE_ID
            };

            struct Varyings
            {
                float4 positionCS : SV_POSITION;
                float2 uv : TEXCOORD0;
                float3 worldPos : TEXCOORD1;
                UNITY_VERTEX_OUTPUT_STEREO
            };

            CBUFFER_START(UnityPerMaterial)
                float4 _MainTex_ST;  
                float _Density;
                float2 _Offset;
                float _Radius;
                float _FadeDistance;
                float _UseNearFar;
                float4 _MainColor;
                float4 _NearColor;
                float4 _FarColor;
            CBUFFER_END

            TEXTURE2D(_MainTex);
            SAMPLER(sampler_MainTex);

            Varyings vert(Attributes input)
            {
                Varyings output;
                UNITY_SETUP_INSTANCE_ID(input);
                UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(output);
                output.positionCS = TransformObjectToHClip(input.positionOS.xyz);
                output.worldPos = TransformObjectToWorld(input.positionOS.xyz);

                // 应用密度（重复次数）和偏移
                output.uv = input.uv * _Density + _Offset;

                return output;
            }

            half4 frag(Varyings input) : SV_Target
            {
                // 采样纹理（RGBA）
                half4 texColor = SAMPLE_TEXTURE2D(_MainTex, sampler_MainTex, input.uv);

                // 用纹理的Alpha作为形状（十字部分不透明）
                float shapeAlpha = texColor.a;

                // 计算距离淡出透明度
                float dist = distance(input.worldPos, _WorldSpaceCameraPos);
                float distanceAlpha = 1.0;
                if (dist > _Radius)
                {
                    float fade = (dist - _Radius) / max(_FadeDistance, 0.001);
                    distanceAlpha = 1.0 - saturate(fade);
                }

                // 颜色选择（是否双色渐变）
                half3 colorTint;
                if (_UseNearFar > 0.5)
                {
                    float t = saturate((dist - _Radius) / max(_FadeDistance, 0.001));
                    colorTint = lerp(_NearColor.rgb, _FarColor.rgb, t);
                }
                else
                {
                    colorTint = _MainColor.rgb;
                }

                // 最终颜色：纹理颜色 * 染色
                half4 finalColor;
                finalColor.rgb = texColor.rgb * colorTint;

                // 最终透明度 = 形状alpha * 距离alpha
                finalColor.a = shapeAlpha * distanceAlpha;

                return finalColor;
            }
            ENDHLSL
        }
    }
}

靠近后效果如下