#version 330 core

out vec4 FragColor;

uniform vec2 uViewport;
uniform float uMajorStep;
uniform float uMinorStep;
uniform bool uLightMode;

float gridLine(float stepPx) {
    vec2 coord = gl_FragCoord.xy;
    vec2 q = coord / stepPx;

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

    return line;
}

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

    vec3 topCol, botCol, majCol, minCol;
    float majStrength, minStrength;
    float vignettePow, vignetteStrength;

    topCol = vec3(0.99, 0.99, 1.00);
    botCol = vec3(0.94, 0.95, 0.98);

    minorCol = vec3(0.80, 0.82, 0.87);
    majorCol = vec3(0.70, 0.73, 0.80);

    minorStrength = 0.22;
    majorStrength = 0.35;
    vignettePow = 0.12;
    vignetteStrength = 0.35;

    vec3 col = mix(botCol, topCol, uv.y);
    float minor = gridLine(max(uMinorStep, 1.0));
    float major = gridLine(max(uMajorStep, 1.0));

    col = mix(col, minorCol, minStrength * minor);
    col = mix(col, majorCol, majStrength * major);

    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);
}