#version 330 core
out vec4 FragColor;

uniform vec2 uViewport;
uniform float uMinorStep;
uniform float uMajorStep;

float gridLine(float stepPx) {
    // 当前坐标像素
    vec2 coord = gl_FragCoord.xy;
    vec2 q = coord / stepPx;

    vec2 g = abs(fract(q - 0.5) - 0.5) / fwidth(q);
    float line = 1.0 - min(min(g.x, g.y), 1.0);
    return line;
}

void main() {
    vec2 viewport = max(uViewport, vec2(1.0));
    vec2 uv = gl_FragCoord.xy / viewport;

    vec3 topCol = vec3(0.99, 0.99, 1.00);
    vec3 botCol = vec3(0.94, 0.95, 0.98);
    vec3 col = mix(botCol, topCol, uv.y);

    float minor = gridLine(max(uMinorStep, 1.0));
    float major = gridLine(max(uMajorStep, 1.0));
    vec3 minorCol = vec3(0.80, 0.82, 0.87);
    vec3 majorcol = vec3(0.70, 0.73, 0.80);
    col = mix(col, minorCol, minor * 0.22);
    col = mix(col, majorcol, major * 0.35);
    vec2 p = uv * 2.0 - 1.0;
    float v = clamp(1.0 - dot(p, p) * 0.12, 0.0, 1.0);
    col *= mix(1.0, v, 0.35);

    FragColor = vec4(col, 1.0);
}