#version 300 es

precision mediump float;

layout(std140) uniform Uniforms {
    float startDate;
    float endDate;
    float currentDate;
    float radius;
    float d;
    float padding1;  // 填充以对齐到8字节边界
    vec2 viewportSize;
};

struct Instant {
    vec2 position;
    vec4 color;
};

in Instant i_instant;

out vec4 FragColor;

float sdVesica(vec2 p, float r, float d)
{
    p = abs(p);
    float b = sqrt(r*r-d*d);  // can delay this sqrt by rewriting the comparison
    return ((p.y-b)*d > p.x*b) ? length(p-vec2(0.0,b))*sign(d)
                               : length(p-vec2(-d,0.0))-r;
}

void main() {
    vec2 p = gl_FragCoord.xy - i_instant.position;
    float sdf = sdVesica(p, radius, d);

    // 简化逻辑：内部完全不透明，外部丢弃
    if (sdf > 0.0) {
        discard;
    }

    // 测试：固定颜色确保能看到
    FragColor = vec4(1.0, 1.0, 1.0, 1.0); // 纯白色
}