Shader "Custom/ParticleUnlitLocalYGradient"
{
    Properties
    {
        _Color1 ("Color 1", Color) = (1, 1, 1, 1)
        _Color2 ("Color 2", Color) = (0, 0, 0, 1)
        _GradientRange ("Gradient Range", Vector) = (0, 1, 0, 0)
    }
    SubShader
    {
        Tags { "Queue" = "Overlay" }
        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #pragma exclude_renderers gles xbox360 ps3

            struct appdata_t
            {
                float4 vertex : POSITION;
                float4 color : COLOR;
            };

            struct v2f
            {
                float4 pos : POSITION;
                float4 color : COLOR;
                float localY : TEXCOORD0;
            };

            float4 _Color1;
            float4 _Color2;
            float4 _GradientRange; // xy 是范围的最小值和最大值

            v2f vert (appdata_t v)
            {
                v2f o;
                o.pos = UnityObjectToClipPos(v.vertex);
                o.color = v.color;
                
                // 将模型空间的 Y 坐标传递到片段着色器
                o.localY = v.vertex.y;
                return o;
            }

            fixed4 frag (v2f i) : SV_Target
            {
                // 计算渐变的值
                float gradient = (i.localY - _GradientRange.x) / (_GradientRange.y - _GradientRange.x);
                gradient = clamp(gradient, 0.0, 1.0); // 确保渐变值在 0 到 1 之间

                // 线性插值两种颜色
                fixed4 interpolatedColor = lerp(_Color1, _Color2, gradient);
                return interpolatedColor * i.color;
            }
            ENDCG
        }
    }
    FallBack "Diffuse"
}