Raw source
#include <stdlib.h> // card > pixar.ppm
#include <stdio.h>
#include <math.h>

struct Vec {
    float x, y, z;

    Vec(float v = 0) { x = y = z = v; }

    Vec(float a, float b, float c = 0) {
      x = a;
      y = b;
      z = c;
    }

    Vec operator+(Vec r) { return Vec(x + r.x, y + r.y, z + r.z); }

    Vec operator*(Vec r) { return Vec(x * r.x, y * r.y, z * r.z); }

    float operator%(Vec r) { return x * r.x + y * r.y + z * r.z; }

    // intnv square root
    Vec operator!() {
      return *this * (1 / sqrtf(*this % *this)
      );
    }
};

float min(float l, float r) { return l < r ? l : r; }

float randomVal() { return (float) rand() / RAND_MAX; }

// Rectangle CSG equation. Returns minimum signed distance from
// space carved by
// lowerLeft vertex and opposite rectangle vertex upperRight.
float BoxTest(Vec position, Vec lowerLeft, Vec upperRight) {
  lowerLeft = position + lowerLeft * -1;
  upperRight = upperRight + position * -1;
  return -min(
          min(
                  min(lowerLeft.x, upperRight.x),
                  min(lowerLeft.y, upperRight.y)),
          min(lowerLeft.z, upperRight.z));
}

#define HIT_NONE 0
#define HIT_LETTER 1
#define HIT_WALL 2
#define HIT_SUN 3

// Sample the world using Signed Distance Fields.
float QueryDatabase(Vec position, int &hitType) {
  float distance = 1e9;
  Vec f = position; // Flattened position (z=0)
  f.z = 0;
  char letters[15*4+1] =               // 15 two points lines
          "5O5_" "5W9W" "5_9_"         // P (without curve)
          "AOEO" "COC_" "A_E_"         // I
          "IOQ_" "I_QO"                // X
          "UOY_" "Y_]O" "WW[W"         // A
          "aOa_" "aWeW" "a_e_" "cWiO"; // R (without curve)

  for (int i = 0; i < sizeof(letters); i += 4) {
    Vec begin = Vec(letters[i] - 79, letters[i + 1] - 79) * .5;
    Vec e = Vec(letters[i + 2] - 79, letters[i + 3] - 79) * .5 + begin * -1;
    Vec o = f + (begin + e * min(-min((begin + f * -1) % e / (e % e),
                                      0),
                                 1)
                ) * -1;
    distance = min(distance, o % o); // compare squared distance.
  }
  distance = sqrtf(distance); // Get real distance, not square distance.

  // Two curves (for P and R in PixaR) with hard-coded locations.
  Vec curves[] = {Vec(-11, 6), Vec(11, 6)};
  for (int i = 2; i--;) {
    Vec o = f + curves[i] * -1;
    distance = min(distance,
                   o.x > 0 ? fabsf(sqrtf(o % o) - 2)
                           : (o.y += o.y > 0 ? -2 : 2, sqrtf(o % o))
               );
  }
  distance = powf(powf(distance, 8) + powf(position.z, 8), .125) - .5;
  hitType = HIT_LETTER;

  float roomDist ;
  roomDist = min(// min(A,B) = Union with Constructive solid geometry
               //-min carves an empty space
                -min(// Lower room
                     BoxTest(position, Vec(-30, -.5, -30), Vec(30, 18, 30)),
                     // Upper room
                     BoxTest(position, Vec(-25, 17, -25), Vec(25, 20, 25))
                ),
                BoxTest( // Ceiling "planks" spaced 8 units apart.
                  Vec(fmodf(fabsf(position.x), 8),
                      position.y,
                      position.z),
                  Vec(1.5, 18.5, -25),
                  Vec(6.5, 20, 25)
                )
  );
  if (roomDist < distance) distance = roomDist, hitType = HIT_WALL;

  float sun = 19.9 - position.y ; // Everything above 19.9 is light source.
  if (sun < distance)distance = sun, hitType = HIT_SUN;

  return distance;
}

// Perform signed sphere marching
// Returns hitType 0, 1, 2, or 3 and update hit position/normal
int RayMarching(Vec origin, Vec direction, Vec &hitPos, Vec &hitNorm) {
  int hitType = HIT_NONE;
  int noHitCount = 0;
  float d; // distance from closest object in world.

  // Signed distance marching
  for (float total_d=0; total_d < 100; total_d += d)
    if ((d = QueryDatabase(hitPos = origin + direction * total_d, hitType)) < .01
            || ++noHitCount > 99)
      return hitNorm =
         !Vec(QueryDatabase(hitPos + Vec(.01, 0), noHitCount) - d,
              QueryDatabase(hitPos + Vec(0, .01), noHitCount) - d,
              QueryDatabase(hitPos + Vec(0, 0, .01), noHitCount) - d)
         , hitType; // Weird return statement where a variable is also updated.
  return 0;
}

Vec Trace(Vec origin, Vec direction) {
  Vec sampledPosition, normal, color, attenuation = 1;
  Vec lightDirection(!Vec(.6, .6, 1)); // Directional light

  for (int bounceCount = 3; bounceCount--;) {
    int hitType = RayMarching(origin, direction, sampledPosition, normal);
    if (hitType == HIT_NONE) break; // No hit. This is over, return color.
    if (hitType == HIT_LETTER) { // Specular bounce on a letter. No color acc.
      direction = direction + normal * ( normal % direction * -2);
      origin = sampledPosition + direction * 0.1;
      attenuation = attenuation * 0.2; // Attenuation via distance traveled.
    }
    if (hitType == HIT_WALL) { // Wall hit uses color yellow?
      float incidence = normal % lightDirection;
      float p = 6.283185 * randomVal();
      float c = randomVal();
      float s = sqrtf(1 - c);
      float g = normal.z < 0 ? -1 : 1;
      float u = -1 / (g + normal.z);
      float v = normal.x * normal.y * u;
      direction = Vec(v,
                      g + normal.y * normal.y * u,
                      -normal.y) * (cosf(p) * s)
                  +
                  Vec(1 + g * normal.x * normal.x * u,
                      g * v,
                      -g * normal.x) * (sinf(p) * s) + normal * sqrtf(c);
      origin = sampledPosition + direction * .1;
      attenuation = attenuation * 0.2;
      if (incidence > 0 &&
          RayMarching(sampledPosition + normal * .1,
                      lightDirection,
                      sampledPosition,
                      normal) == HIT_SUN)
        color = color + attenuation * Vec(500, 400, 100) * incidence;
    }
    if (hitType == HIT_SUN) { //
      color = color + attenuation * Vec(50, 80, 100); break; // Sun Color
    }
  }
  return color;
}

int main(int argc, char** argv) {
  int w = 960, h = 540, samplesCount = 1;
  Vec position(-22, 5, 25);
  Vec goal = !(Vec(-3, 4, 0) + position * -1);
  Vec left = !Vec(goal.z, 0, -goal.x) * (1. / w);

  if (argc > 1 ) {
    samplesCount = atoi(argv[1]);
  }    

  // Cross-product to get the up vector
  Vec up(goal.y * left.z - goal.z * left.y,
      goal.z * left.x - goal.x * left.z,
      goal.x * left.y - goal.y * left.x);

  printf("P6 %d %d 255 ", w, h);
  for (int y = h; y--;)
    for (int x = w; x--;) {
      Vec color;
      for (int p = samplesCount; p--;)
        color = color + Trace(position, !(goal + left * (x - w / 2 + randomVal()) + up * (y - h / 2 + randomVal())));

      // Reinhard tone mapping
      color = color * (1. / samplesCount) + 14. / 241;
      Vec o = color + 1;
      color = Vec(color.x / o.x, color.y / o.y, color.z / o.z) * 255;
      printf("%c%c%c", (int) color.x, (int) color.y, (int) color.z);
    }
}// Andrew Kensler