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varying vec2 pos;
uniform float u_aspect_ratio;
uniform float u_time;
#define PI 3.14159265
#define TAU 6.28318530718
float rand(vec2 co) {
return fract(sin(dot(co, vec2(12.9898,78.233))) * 43758.5453);
}
// see https://en.wikipedia.org/wiki/HSL_and_HSV#HSV_to_RGB_alternative
float hsvf(float n, vec3 hsv) {
float k = mod(n + hsv.x * 6.0, 6.0);
return hsv.z - hsv.z * hsv.y * clamp(min(k, 4.0 - k), 0.0, 1.0);
}
vec3 hsv_to_rgb(vec3 hsv) {
return vec3(hsvf(5.0, hsv), hsvf(3.0, hsv), hsvf(1.0, hsv));
}
// see https://en.wikipedia.org/wiki/Error_function#Inverse_functions
float inv_erf(float z) {
return 0.5 * sqrt(PI) * z *
(1.0 + z * z *
(0.2617993878 + z * z *
(0.1439317308 + z * z *
(0.0976636195 + z * z *
(0.0732990794 + z * z *
(0.0583725009))))));
}
float distance2(vec2 a, vec2 b) {
return dot(a-b, a-b);
}
// inverse of the normal cumulative density function
// see https://en.wikipedia.org/wiki/Normal_distribution#Quantile_function
float inv_norm(float p, float mu, float sigma) {
return mu + sigma * sqrt(2.0) * inv_erf(2.0 * p - 1.0);
}
void main() {
vec3 p = vec3(pos, u_time);
p.x *= u_aspect_ratio;
float z = p.z;
float t = 0.0;
for (float i = 0.0; i < 10.0; i += 1.0) {
float r = rand(vec2(i + 1.0, i + 1.0));
vec2 loc = vec2(
sin(1.0 * z * r),
tan(1.0 * z * r)
);
loc *= 0.5;
loc += 0.5;
loc.x *= u_aspect_ratio;
float term = 1.0 - distance(p.xy, loc);
term = clamp(term, 0.0, 1.0);
t = max(t, term);
}
float n = 2.0 + 2.0 * (0.5 + 0.5 * sin(z));
t = fract(t*n);
t *= pow(sin(t * 40.0), 6.0 * pow(0.5 + 0.5 * sin(z), 3.0));
float v = t < 0.5 ? 0.0 : 1.0;
float h = max(t - 0.5, 0.0) * 2.0;
h *= 0.2;
h += 0.7;
float s = 1.0;
vec3 hsv = vec3(h, s, v);
gl_FragColor = vec4(hsv_to_rgb(hsv), 1.0);
}
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