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#include<graphics.h>#include<conio.h>#include <math.h> // fabsf(), fminf(), fmaxf(), sinf(), cosf(), sqrt()#include <stdlib.h> // rand(), RAND_MAX
#define TWO_PI 6.28318530718f#define W 1024#define H 1024#define N 256#define MAX_STEP 64#define MAX_DISTANCE 5.0f#define EPSILON 1e-6f#define BIAS 1e-4f#define MAX_DEPTH 3#define BLACK { 0.0f, 0.0f, 0.0f }
typedef struct { float r, g, b; } Color;typedef struct { float sd, reflectivity, eta; Color emissive, absorption; } Result;
unsigned char img[W * H * 3];
Color colorAdd(Color a, Color b) {  Color c = { a.r + b.r, a.g + b.g, a.b + b.b };  return c;}
Color colorMultiply(Color a, Color b) {  Color c = { a.r * b.r, a.g * b.g, a.b * b.b };  return c;}
Color colorScale(Color a, float s) {  Color c = { a.r * s, a.g * s, a.b * s };  return c;}
float circleSDF(float x, float y, float cx, float cy, float r) {  float ux = x - cx, uy = y - cy;  return sqrtf(ux * ux + uy * uy) - r;}
float planeSDF(float x, float y, float px, float py, float nx, float ny) {  return (x - px) * nx + (y - py) * ny;}
float ngonSDF(float x, float y, float cx, float cy, float r, float n) {  float ux = x - cx, uy = y - cy, a = TWO_PI / n;  float t = fmodf(atan2f(uy, ux) + TWO_PI, a), s = sqrtf(ux * ux + uy * uy);  return planeSDF(s * cosf(t), s * sinf(t), r, 0.0f, cosf(a * 0.5f), sinf(a * 0.5f));}
Result unionOp(Result a, Result b) {  return a.sd < b.sd ? a : b;}
Result intersectOp(Result a, Result b) {  return a.sd > b.sd ? a : b;}
Result scene(float x, float y) {  float u = x - 0.5f, v = y - 0.5f, t = fmodf(atan2f(v, u) + TWO_PI, TWO_PI / 16), s = sqrtf(u * u + v * v);  x = fabsf(x - 0.5f) + 0.5f;  Color m = { 0.0f, 3.0f, 3.0f };  Result a = { ngonSDF(x, y, 0.7f, 0.35f, 0.2f, 16), 0.0f, 1.77f, BLACK, m };  Result b = { ngonSDF(x, y, 0.35f, 0.35f, 0.55f, 32), 0.0f, 1.77f, BLACK, m };  Result c = { planeSDF(x, y, 0.5f, 0.35f, 0.0f, -1.0f), 0.0f, 1.77f, BLACK, m };  // y = fabsf(y - 0.5f) + 0.5f;  // Result d = { circleSDF(x, y, 1.05f, 1.05f, 0.05f), 0.0f, 0.0f, { 5.0f, 5.0f, 5.0f }, BLACK };  // Result d = { -circleSDF(x, y, 0.5f, 0.5f, 3.0f), 0.0f, 0.0f, { 0.5f, 0.5f, 0.5f }, BLACK };  Result d = { circleSDF(s * cosf(t), s * sinf(t), 0.6f * cosf(TWO_PI / 32), 0.5f * sinf(TWO_PI / 32), 0.05f), 0.0f, 0.0f, { 2.0f, 2.0f, 2.0f }, BLACK };  return unionOp(unionOp(a, intersectOp(b, c)), d);}
void gradient(float x, float y, float* nx, float* ny) {  *nx = (scene(x + EPSILON, y).sd - scene(x - EPSILON, y).sd) * (0.5f / EPSILON);  *ny = (scene(x, y + EPSILON).sd - scene(x, y - EPSILON).sd) * (0.5f / EPSILON);}
void reflect(float ix, float iy, float nx, float ny, float* rx, float* ry) {  float idotn2 = (ix * nx + iy * ny) * 2.0f;  *rx = ix - idotn2 * nx;  *ry = iy - idotn2 * ny;}
int refract(float ix, float iy, float nx, float ny, float eta, float* rx, float* ry) {  float idotn = ix * nx + iy * ny;  float k = 1.0f - eta * eta * (1.0f - idotn * idotn);  if (k < 0.0f)    return 0; // Total internal reflection  float a = eta * idotn + sqrtf(k);  *rx = eta * ix - a * nx;  *ry = eta * iy - a * ny;  return 1;}
float fresnel(float cosi, float cost, float etai, float etat) {  float rs = (etat * cosi - etai * cost) / (etat * cosi + etai * cost);  float rp = (etai * cosi - etat * cost) / (etai * cosi + etat * cost);  return (rs * rs + rp * rp) * 0.5f;}
Color beerLambert(Color a, float d) {  Color c = { expf(-a.r * d), expf(-a.g * d), expf(-a.b * d) };  return c;}
Color trace(float ox, float oy, float dx, float dy, int depth) {  float t = 1e-3f;  float sign = scene(ox, oy).sd > 0.0f ? 1.0f : -1.0f;  for (int i = 0; i < MAX_STEP && t < MAX_DISTANCE; i++) {    float x = ox + dx * t, y = oy + dy * t;    Result r = scene(x, y);    if (r.sd * sign < EPSILON) {      Color sum = r.emissive;      if (depth < MAX_DEPTH && r.eta > 0.0f) {        float nx, ny, rx, ry, refl = r.reflectivity;        gradient(x, y, &nx, &ny);        float s = 1.0f / (nx * nx + ny * ny);        nx *= sign * s;        ny *= sign * s;        if (r.eta > 0.0f) {          if (refract(dx, dy, nx, ny, sign < 0.0f ? r.eta : 1.0f / r.eta, &rx, &ry)) {            float cosi = -(dx * nx + dy * ny);            float cost = -(rx * nx + ry * ny);            refl = sign < 0.0f ? fresnel(cosi, cost, r.eta, 1.0f) : fresnel(cosi, cost, 1.0f, r.eta);            refl = fmaxf(fminf(refl, 1.0f), 0.0f);            sum = colorAdd(sum, colorScale(trace(x - nx * BIAS, y - ny * BIAS, rx, ry, depth + 1), 1.0f - refl));          }          else            refl = 1.0f; // Total internal reflection        }        if (refl > 0.0f) {          reflect(dx, dy, nx, ny, &rx, &ry);          sum = colorAdd(sum, colorScale(trace(x + nx * BIAS, y + ny * BIAS, rx, ry, depth + 1), refl));        }      }      Color c = colorMultiply(sum, beerLambert(r.absorption, t));      return c;    }    t += r.sd * sign;  }  Color black = BLACK;  return black;}
Color sample(float x, float y) {  Color sum = BLACK;  for (int i = 0; i < N; i++) {    float a = TWO_PI * (i + (float)rand() / RAND_MAX) / N;    sum = colorAdd(sum, trace(x, y, cosf(a), sinf(a), 0));  }  return colorScale(sum, 1.0f / N);}
int main() {  initgraph(W, H);  unsigned char* p = img;  for (int y = 0; y < H; y++)  {    for (int x = 0; x < W; x++, p += 3) {      Color c = sample((float)x / W, (float)y / H);      p[0] = (int)(fminf(c.r * 255.0f, 255.0f));      p[1] = (int)(fminf(c.g * 255.0f, 255.0f));      p[2] = (int)(fminf(c.b * 255.0f, 255.0f));      putpixel(x, y, RGB(p[0], p[1], p[2]));    }  }  _getch();}