Shader "Custom/ModelLocalBlend"
{
    Properties
    {
        _MainTexA("Texture A", 2D) = "white" {}
        _MainTexB("Texture B", 2D) = "white" {}
        _BlendAxis("Blend Axis (X=1,Y=1,Z=1)", Vector) = (1, 0, 0, 0)
        _BlendCenter("Blend Center", Float) = 0.0
        _BlendWidth("Blend Width", Float) = 1.0
    }

        SubShader
        {
            Tags { "RenderType" = "Opaque" }
            Pass
            {
                CGPROGRAM
                #pragma vertex vert
                #pragma fragment frag
                #include "UnityCG.cginc"

                sampler2D _MainTexA;
                sampler2D _MainTexB;
                float4 _MainTexA_ST;
                float4 _MainTexB_ST;
                float4 _BlendAxis;     // 模型空间融合方向
                float _BlendCenter;    // 融合中心（模型局部坐标）
                float _BlendWidth;

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

                struct v2f
                {
                    float4 vertex : SV_POSITION;
                    float2 uvA : TEXCOORD0;
                    float2 uvB : TEXCOORD1;
                    float3 localPos : TEXCOORD2;
                };

                v2f vert(appdata v)
                {
                    v2f o;
                    o.vertex = UnityObjectToClipPos(v.vertex);
                    o.uvA = TRANSFORM_TEX(v.uv, _MainTexA);
                    o.uvB = TRANSFORM_TEX(v.uv, _MainTexB);
                    o.localPos = v.vertex.xyz; // 模型局部坐标
                    return o;
                }

                fixed4 frag(v2f i) : SV_Target
                {
                    float proj = dot(i.localPos, normalize(_BlendAxis.xyz));
                    float start = _BlendCenter - _BlendWidth * 0.5;
                    float blendFactor = saturate((proj - start) / _BlendWidth);

                    fixed4 colA = tex2D(_MainTexA, i.uvA);
                    fixed4 colB = tex2D(_MainTexB, i.uvB);
                    return lerp(colA, colB, blendFactor);
                }
                ENDCG
            }
        }
}