TH1/Unity/Assets/Shaders/GrayScaleShader.shader

Shader "Custom/GrayScale"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}  // 纹理贴图
        _GrayAmount ("Gray Amount", Range(0, 1)) = 1 // 置灰强度
    }
    
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100
        Cull Off  // 允许渲染翻转的面，防止 scale.x = -1 被剔除

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

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

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

            sampler2D _MainTex;
            float _GrayAmount;

            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);
                
                // 仅对 alpha > 0.95 的像素进行置灰
                if (col.a > 0.95)
                {
                    float gray = dot(col.rgb, float3(0.299, 0.587, 0.114));
                    col.rgb = lerp(col.rgb, gray, _GrayAmount);
                }

                return col;
            }
            ENDCG
        }
    }
}