Unveiling the Enigma: Delving Deep into Shader Artistry and Self-Reflection

// CC0: Let's self reflect

//  Always enjoyed the videos of Platonic solids with inner mirrors

//  I made some previous attempts but thought I make another attempt it



// Reducing the alias effects on the inner reflections turned out to be a bit tricky. 

//  Simplest solution is just to run run fullscreen on a 4K screen ;)



// Function to generate the solid found here: https://www.shadertoy.com/view/MsKGzw



// Tinker with these parameters to create different solids

// -------------------------------------------------------

const float rotation_speed= 0.25;



const float poly_U        = 1.;   // [0, inf]

const float poly_V        = 0.5;  // [0, inf]

const float poly_W        = 1.0;  // [0, inf]

const int   poly_type     = 3;    // [2, 5]

const float poly_zoom     = 2.0;



const float inner_sphere  = 1.;



const float refr_index    = 0.9;



#define MAX_BOUNCES2        6

// -------------------------------------------------------







#define TIME        iTime

#define RESOLUTION  iResolution

#define PI          3.141592654

#define TAU         (2.0*PI)



// License: WTFPL, author: sam hocevar, found: https://stackoverflow.com/a/17897228/418488

const vec4 hsv2rgb_K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);

vec3 hsv2rgb(vec3 c) {

  vec3 p = abs(fract(c.xxx + hsv2rgb_K.xyz) * 6.0 - hsv2rgb_K.www);

  return c.z * mix(hsv2rgb_K.xxx, clamp(p - hsv2rgb_K.xxx, 0.0, 1.0), c.y);

}

// License: WTFPL, author: sam hocevar, found: https://stackoverflow.com/a/17897228/418488

//  Macro version of above to enable compile-time constants

#define HSV2RGB(c)  (c.z * mix(hsv2rgb_K.xxx, clamp(abs(fract(c.xxx + hsv2rgb_K.xyz) * 6.0 - hsv2rgb_K.www) - hsv2rgb_K.xxx, 0.0, 1.0), c.y))



#define TOLERANCE2          0.0005

//#define MAX_RAY_LENGTH2   10.0

#define MAX_RAY_MARCHES2    50

#define NORM_OFF2           0.005

#define BACKSTEP2



#define TOLERANCE3          0.0005

#define MAX_RAY_LENGTH3     10.0

#define MAX_RAY_MARCHES3    90

#define NORM_OFF3           0.005



const vec3 rayOrigin    = vec3(0.0, 1., -5.);

const vec3 sunDir       = normalize(-rayOrigin);





const vec3 sunCol       = HSV2RGB(vec3(0.06 , 0.90, 1E-2))*1.;

const vec3 bottomBoxCol = HSV2RGB(vec3(0.66, 0.80, 0.5))*1.;

const vec3 topBoxCol    = HSV2RGB(vec3(0.60, 0.90, 1.))*1.;

const vec3 glowCol0     = HSV2RGB(vec3(0.05 , 0.7, 1E-3))*1.;

const vec3 glowCol1     = HSV2RGB(vec3(0.95, 0.7, 1E-3))*1.;

const vec3 beerCol      = -HSV2RGB(vec3(0.15+0.5, 0.7, 2.)); 

const float rrefr_index = 1./refr_index;





// License: Unknown, author: knighty, found: https://www.shadertoy.com/view/MsKGzw

const float poly_cospin   = cos(PI/float(poly_type));

const float poly_scospin  = sqrt(0.75-poly_cospin*poly_cospin);

const vec3  poly_nc       = vec3(-0.5, -poly_cospin, poly_scospin);

const vec3  poly_pab      = vec3(0., 0., 1.);

const vec3  poly_pbc_     = vec3(poly_scospin, 0., 0.5);

const vec3  poly_pca_     = vec3(0., poly_scospin, poly_cospin);

const vec3  poly_p        = normalize((poly_U*poly_pab+poly_V*poly_pbc_+poly_W*poly_pca_));

const vec3  poly_pbc      = normalize(poly_pbc_);

const vec3  poly_pca      = normalize(poly_pca_);



mat3 g_rot;

vec2 g_gd;



// License: MIT, author: Inigo Quilez, found: https://iquilezles.org/articles/noacos/

mat3 rot(vec3 d, vec3 z) {

  vec3  v = cross( z, d );

  float c = dot( z, d );

  float k = 1.0/(1.0+c);



  return mat3( v.x*v.x*k + c,     v.y*v.x*k - v.z,    v.z*v.x*k + v.y,

               v.x*v.y*k + v.z,   v.y*v.y*k + c,      v.z*v.y*k - v.x,

               v.x*v.z*k - v.y,   v.y*v.z*k + v.x,    v.z*v.z*k + c    );

}



// License: Unknown, author: Matt Taylor (https://github.com/64), found: https://64.github.io/tonemapping/

vec3 aces_approx(vec3 v) {

  v = max(v, 0.0);

  v *= 0.6;

  float a = 2.51;

  float b = 0.03;

  float c = 2.43;

  float d = 0.59;

  float e = 0.14;

  return clamp((v*(a*v+b))/(v*(c*v+d)+e), 0.0, 1.0);

}



float sphere(vec3 p, float r) {

  return length(p) - r;

}



// License: MIT, author: Inigo Quilez, found: https://iquilezles.org/articles/distfunctions/

float box(vec2 p, vec2 b) {

  vec2 d = abs(p)-b;

  return length(max(d,0.0)) + min(max(d.x,d.y),0.0);

}



// License: Unknown, author: knighty, found: https://www.shadertoy.com/view/MsKGzw

void poly_fold(inout vec3 pos) {

  vec3 p = pos;



  for(int i = 0; i < poly_type; ++i){

    p.xy  = abs(p.xy);

    p    -= 2.*min(0., dot(p,poly_nc)) * poly_nc;

  }



  pos = p;

}



float poly_plane(vec3 pos) {

  float d0 = dot(pos, poly_pab);

  float d1 = dot(pos, poly_pbc);

  float d2 = dot(pos, poly_pca);

  float d = d0;

  d = max(d, d1);

  d = max(d, d2);

  return d;

}



float poly_corner(vec3 pos) {

  float d = length(pos) - .0125;

  return d;

}



float dot2(vec3 p) {

  return dot(p, p);

}



float poly_edge(vec3 pos) {

  float dla = dot2(pos-min(0., pos.x)*vec3(1., 0., 0.));

  float dlb = dot2(pos-min(0., pos.y)*vec3(0., 1., 0.));

  float dlc = dot2(pos-min(0., dot(pos, poly_nc))*poly_nc);

  return sqrt(min(min(dla, dlb), dlc))-2E-3;

}



vec3 shape(vec3 pos) {

  pos *= g_rot;

  pos /= poly_zoom;

  poly_fold(pos);

  pos -= poly_p;



  return vec3(poly_plane(pos), poly_edge(pos), poly_corner(pos))*poly_zoom;

}



vec3 render0(vec3 ro, vec3 rd) {

  vec3 col = vec3(0.0);



  float srd  = sign(rd.y);

  float tp   = -(ro.y-6.)/abs(rd.y);



  if (srd < 0.) {

    col += bottomBoxCol*exp(-0.5*(length((ro + tp*rd).xz)));

  }



  if (srd > 0.0) {

    vec3 pos  = ro + tp*rd;

    vec2 pp = pos.xz;

    float db = box(pp, vec2(5.0, 9.0))-3.0;



    col += topBoxCol*rd.y*rd.y*smoothstep(0.25, 0.0, db);

    col += 0.2*topBoxCol*exp(-0.5*max(db, 0.0));

    col += 0.05*sqrt(topBoxCol)*max(-db, 0.0);

  }





  col += sunCol/(1.001-dot(sunDir, rd));

  return col; 

}



float df2(vec3 p) {

  vec3 ds = shape(p);

  float d2 = ds.y-5E-3;

  float d0 = min(-ds.x, d2);

  float d1 = sphere(p, inner_sphere);

  g_gd = min(g_gd, vec2(d2, d1));

  float d = (min(d0, d1));

  return d;

}



float rayMarch2(vec3 ro, vec3 rd, float tinit) {

  float t = tinit;

#if defined(BACKSTEP2)

  vec2 dti = vec2(1e10,0.0);

#endif

  int i;

  for (i = 0; i < MAX_RAY_MARCHES2; ++i) {

    float d = df2(ro + rd*t);

#if defined(BACKSTEP2)

    if (d<dti.x) { dti=vec2(d,t); }

#endif  

    // Bouncing in a closed shell, will never miss

    if (d < TOLERANCE2/* || t > MAX_RAY_LENGTH3 */) {

      break;

    }

    t += d;

  }

#if defined(BACKSTEP2)

  if(i==MAX_RAY_MARCHES2) { t=dti.y; };

#endif  

  return t;

}



vec3 normal2(vec3 pos) {

  vec2  eps = vec2(NORM_OFF2,0.0);

  vec3 nor;

  nor.x = df2(pos+eps.xyy) - df2(pos-eps.xyy);

  nor.y = df2(pos+eps.yxy) - df2(pos-eps.yxy);

  nor.z = df2(pos+eps.yyx) - df2(pos-eps.yyx);

  return normalize(nor);

}



vec3 render2(vec3 ro, vec3 rd, float db) {

  vec3 agg = vec3(0.0);

  float ragg = 1.;

  float tagg = 0.;



  for (int bounce = 0; bounce < MAX_BOUNCES2; ++bounce) {

    if (ragg < 0.1) break;

    g_gd      = vec2(1E3);

    float t2  = rayMarch2(ro, rd, min(db+0.05, 0.3));

    vec2 gd2  = g_gd;

    tagg      += t2;



    vec3 p2   = ro+rd*t2;

    vec3 n2   = normal2(p2);

    vec3 r2   = reflect(rd, n2);

    vec3 rr2  = refract(rd, n2, rrefr_index);

    float fre2= 1.+dot(n2,rd);



    vec3 beer = ragg*exp(0.2*beerCol*tagg);

    agg += glowCol1*beer*((1.+tagg*tagg*4E-2)*6./max(gd2.x, 5E-4+tagg*tagg*2E-4/ragg));

    vec3 ocol = 0.2*beer*render0(p2, rr2);

    if (gd2.y <= TOLERANCE2) {

      ragg *= 1.-0.9*fre2;

    } else {

      agg     += ocol;

      ragg    *= 0.8;

    }



    ro        = p2;

    rd        = r2;

    db        = gd2.x; 

  }





  return agg;

}



float df3(vec3 p) {

  vec3 ds = shape(p);

  g_gd = min(g_gd, ds.yz);

  const float sw = 0.02;

  float d1 = min(ds.y, ds.z)-sw;

  float d0 = ds.x;

  d0 = min(d0, ds.y);

  d0 = min(d0, ds.z);

  return d0;

}



float rayMarch3(vec3 ro, vec3 rd, float tinit, out int iter) {

  float t = tinit;

  int i;

  for (i = 0; i < MAX_RAY_MARCHES3; ++i) {

    float d = df3(ro + rd*t);

    if (d < TOLERANCE3 || t > MAX_RAY_LENGTH3) {

      break;

    }

    t += d;

  }

  iter = i;

  return t;

}



vec3 normal3(vec3 pos) {

  vec2  eps = vec2(NORM_OFF3,0.0);

  vec3 nor;

  nor.x = df3(pos+eps.xyy) - df3(pos-eps.xyy);

  nor.y = df3(pos+eps.yxy) - df3(pos-eps.yxy);

  nor.z = df3(pos+eps.yyx) - df3(pos-eps.yyx);

  return normalize(nor);

}



vec3 render3(vec3 ro, vec3 rd) {

  int iter;



  vec3 skyCol = render0(ro, rd);

  vec3 col  = skyCol;



  g_gd      = vec2(1E3);

  float t1  = rayMarch3(ro, rd, 0.1, iter);

  vec2 gd1  = g_gd;

  vec3 p1   = ro+t1*rd;

  vec3 n1   = normal3(p1);

  vec3 r1   = reflect(rd, n1);

  vec3 rr1  = refract(rd, n1, refr_index);

  float fre1= 1.+dot(rd, n1);

  fre1 *= fre1;



  float ifo = mix(0.5, 1., smoothstep(1.0, 0.9, float(iter)/float(MAX_RAY_MARCHES3)));



  if (t1 < MAX_RAY_LENGTH3) {

    col = render0(p1, r1)*(0.5+0.5*fre1)*ifo;

    vec3 icol = render2(p1, rr1, gd1.x); 

    if (gd1.x > TOLERANCE3 && gd1.y > TOLERANCE3 && rr1 != vec3(0.)) {

      col += icol*(1.-0.75*fre1)*ifo;

    }

  }



  col += (glowCol0+1.*fre1*(glowCol0))/max(gd1.x, 3E-4);

  return col;



}





vec3 effect(vec2 p, vec2 pp) {

  const float fov = 2.0;



  const vec3 up = vec3(0., 1., 0.);

  const vec3 la   = vec3(0.0);



  const vec3 ww = normalize(normalize(la-rayOrigin));

  const vec3 uu = normalize(cross(up, ww));

  const vec3 vv = cross(ww, uu);



  vec3 rd = normalize(-p.x*uu + p.y*vv + fov*ww);



  vec3 col = vec3(0.0);

  col = render3(rayOrigin, rd);



  col -= 2E-2*vec3(2.,3.,1.)*(length(p)+0.25);

  col = aces_approx(col);

  col = sqrt(col);

  return col;

}



void mainImage( out vec4 fragColor, in vec2 fragCoord ) {

  vec2 q = fragCoord/RESOLUTION.xy;

  vec2 p = -1. + 2. * q;

  vec2 pp = p;

  p.x *= RESOLUTION.x/RESOLUTION.y;



  float a = TIME*rotation_speed;

  vec3 r0 = vec3(1.0, sin(vec2(sqrt(0.5), 1.0)*a));

  vec3 r1 = vec3(cos(vec2(sqrt(0.5), 1.0)*0.913*a), 1.0);

  mat3 rot = rot(normalize(r0), normalize(r1));

  g_rot = rot;



  vec3 col = effect(p, pp);



  fragColor = vec4(col, 1.0);

}