// Shaders/AdvancedBlend.shader
Shader "Custom/AdvancedBlend" {
    Properties {
        _MainTex ("Base (RGB)", 2D) = "white" {}
        _BlendTex ("Blend Texture", 2D) = "white" {}
        _Position ("Blend Position", Vector) = (0,0,0,0)
        _BlendMode ("Blend Mode", Float) = 0
    }

    SubShader {
        Tags { "RenderType"="Opaque" }
        LOD 100

        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;
            sampler2D _BlendTex;
            float2 _Position;
            float _BlendMode;

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

            fixed4 frag (v2f i) : SV_Target {
                fixed4 base = tex2D(_MainTex, i.uv);
                
                // 计算混合纹理坐标
                float2 blendUV = i.uv - _Position / _ScreenParams.xy;
                if (any(blendUV < 0) || any(blendUV > 1))
                    return base;
                
                fixed4 blend = tex2D(_BlendTex, blendUV);
                
                // 混合模式选择
                switch ((int)_BlendMode) {
                    case 0: // Alpha Blend
                        return lerp(base, blend, blend.a);
                    case 1: // Multiply
                        return base * blend;
                    case 2: // Screen
                        return 1 - (1 - base) * (1 - blend);
                    default:
                        return base;
                }
            }
            ENDCG
        }
    }
}