Adjustable n-fold mirror

GLSL shader by claudegl · created 2026-06-24 · 10s loop · 1 pass

Adjustable n-fold mirror — realtime GLSL.

Tags: glsl, generative, fractal

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Shader source (GLSL)

Common

#define pi acos(-1.)
#define deg pi/180.
#define time iTime*2.*pi/10.
#define R iResolution.xy
#define ar R.x/R.y
#define M iMouse
#define xm (M.xy/R)
#define nm ((xm.xy-0.5)*vec2(ar,1.)+0.5)
mat2 r2d(float a) {
    return mat2(cos(a),sin(a),-sin(a),cos(a));
}

Buffer A (iChannel0)

// ── 04 · Adjustable n-fold kaleidoscope ─────────────────────────────────────
// Slide: symmetry is nearly free. Mirror the ANGLE and structure snaps to
// harmony. Strongest "wow per keystroke" in the deck — drag uFold live.
// ShaderKit: single pass. Slider: uFold (2.0 .. 24.0, default 6.0).
// ───────────────────────────────────────────────────────────────────────────

#define PI 3.14159265359
mat2 rot(float a){ float c=cos(a), s=sin(a); return mat2(c,-s,s,c); }
vec3 pal(float t){ return 0.5+0.5*cos(6.2831*(t+vec3(0.0,0.33,0.67))); }

// a little moving "scene" we view through the mirrors
float scene(vec2 p){
    p *= rot(iTime*0.2);
    float v = sin(p.x*4.0 + iTime) * sin(p.y*4.0 - iTime*0.7);
    v += 0.5*sin(length(p-vec2(0.6,0.2))*10.0 - iTime*2.0);
    return v;
}

void mainImage(out vec4 fragColor, in vec2 fragCoord){
    vec2 uv = (2.0*fragCoord - iResolution.xy)/iResolution.y;

    float uFold = 6.0;                          // <- the live slider
    float r = length(uv);
    float a = atan(uv.y, uv.x);

    // fold the angle into one wedge and mirror it
    float wedge = 2.0*PI/uFold;
    a = mod(a, wedge);
    a = abs(a - wedge*0.5);

    vec2 kp = r*vec2(cos(a), sin(a));
    float v = scene(kp*2.5);

    float glow = 0.5/(abs(v)+0.18);
    vec3 col = pal(r*0.4 + 0.15*iTime) * glow;
    col *= smoothstep(1.7, 0.1, r);
    fragColor = vec4(pow(col, vec3(0.85)), 1.0);
}

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