Shader "Bamboo/CircularProgress"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        _Progress ("Progress", Range(0, 1)) = 0
        _Color ("Color", Color) = (1,1,1,1)
        _BackgroundColor ("Background Color", Color) = (0,0,0,0)
    }
    
    SubShader
    {
        Tags 
        { 
            "Queue"="Transparent" 
            "RenderType"="Transparent" 
        }
        
        Blend SrcAlpha OneMinusSrcAlpha
        Cull Off
        ZWrite Off
        
        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;
            float4 _MainTex_ST;
            float _Progress;
            fixed4 _Color;
            fixed4 _BackgroundColor;
            
            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = TRANSFORM_TEX(v.uv, _MainTex);
                return o;
            }
            
            fixed4 frag (v2f i) : SV_Target
            {
                // 获取UV坐标相对于中心的位置
                float2 center = float2(0.5, 0.5);
                float2 dir = i.uv - center;
                
                // 计算当前点到圆心的距离
                float dist = length(dir);
                
                // 计算当前点的角度（从上方开始顺时针方向）
                // atan2返回[-π, π]，我们转换为[0, 1]范围
                float angle = atan2(dir.x, dir.y) / (2.0 * 3.14159265359);
                angle = angle < 0 ? angle + 1.0 : angle;
                
                // 采样纹理
                fixed4 col = tex2D(_MainTex, i.uv);
                
                // 根据进度决定是否显示
                float visible = (dist <= 0.5) && (angle <= _Progress);
                
                // 混合颜色
                col.rgb = col.rgb * _Color.rgb;
                col.a = col.a * _Color.a * visible;
                
                // 如果不可见，使用背景色
                return lerp(_BackgroundColor, col, visible);
            }
            ENDCG
        }
    }
}