Shader "Unlit/ScreenEffect"
{
    Properties {
        _MainTex ("Base (RGB)", 2D) = "white" {}  //需要处理的渲染纹理
        _Brightness ("Brightness", Float) = 1     //亮度
        _Saturation("Saturation", Float) = 1      //饱和度
        _Contrast("Contrast", Float) = 1          //对比度
    }
    SubShader {
        Pass {  
            ZTest Always Cull Off ZWrite Off
            
            CGPROGRAM  
            #pragma vertex vert  
            #pragma fragment frag  
              
            #include "UnityCG.cginc"  
              
            sampler2D _MainTex;  
            half _Brightness;
            half _Saturation;
            half _Contrast;
              
            struct v2f {
                float4 pos : SV_POSITION;
                half2 uv: TEXCOORD0;
            };
              
            v2f vert(appdata_img v) {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.uv = v.texcoord;
                return o;
            }
        
            fixed4 frag(v2f i) : SV_Target {
                fixed4 renderTex = tex2D(_MainTex, i.uv);  
                  
                // 计算亮度改变后的颜色
                fixed3 finalColor = renderTex.rgb * _Brightness;
                
                // 计算饱和度改变后的颜色
                fixed luminance = 0.2125 * renderTex.r + 0.7154 * renderTex.g + 0.0721 * renderTex.b;
                fixed3 luminanceColor = fixed3(luminance, luminance, luminance);
                finalColor = lerp(luminanceColor, finalColor, _Saturation);
                
                // 计算对比度改变后的颜色
                fixed3 avgColor = fixed3(0.5, 0.5, 0.5);
                finalColor = lerp(avgColor, finalColor, _Contrast);
                
                return fixed4(finalColor, renderTex.a);  
            }  
              
            ENDCG
        }  
    }
    
    Fallback Off
}