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#version 330
out vec4 fragColor;
uniform vec2 res;
uniform float time;
const float sharpness = 300;
const float PI = 3.14159265358979323846;
mat2 rot(float a) {
return mat2(
cos(a), -sin(a),
sin(a), cos(a)
);
}
float circle(vec2 m, float r, vec2 p) {
vec2 diff = m - p;
float d = sqrt(dot(diff, diff));
return clamp((r - d)*sharpness, 0.0, 1.0);
}
float circle_d(vec2 m, float r, vec2 p) {
return circle(m, r, p) - circle(m, r - 1/sharpness, p);
}
float square(vec2 m, float a, float r, vec2 p) {
vec2 diff = abs((m - p) * rot(r));
float d = max(diff.x, diff.y);
return clamp((a - d)*sharpness, 0.0, 1.0);
}
void main(void) {
vec2 m = res/2;
float s = min(m.x, m.y);
vec2 p = (gl_FragCoord.xy - m) / s;
float scene = 0;
int n = 20;
float b = 1;
float alpha = 0;
for (int i = 0; i < n; i++) {
float c;
c = circle_d(vec2(0, 0), b, p);
scene = abs(scene - c);
float delta = mod(time/5000, PI/2);
alpha = mod(alpha + delta, PI/2);
b /= sqrt(2);
c = square(vec2(0, 0), b, alpha, p);
scene = abs(scene - c);
c = square(vec2(0, 0), b, -alpha, p);
scene = abs(scene - c);
}
fragColor = vec4(vec3(1, 1, 1) * scene, 1);
}
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