class Ray {
  float3 o;   // origin
  float3 dir; // direction
};

// Minimum threshold: any point closer to the surface than this is counted as part of it.
const float kMinThreshold = 1e-5;

// Maximum threshold: if we are ever this far away from the surface then assume we will never
// intersect. In practice you'll probably clamp the ray to some bounding volume instead.
const float kMaxThreshold = 1e2;

bool march_ray(Ray& r, SDF f) {
  float distance;
  while(true) {
    // Compute the distance to the surface. We can move this far without intersecting.
    distance = f(r.o);

    // Specifically, we can move this far in the ray direction without intersecting.
    r.o = r.o + distance * r.dir;

    // If we're sufficiently close to the surface, count as an intersection.
    if (distance < kMinThreshold) {
      return true;
    }

    // If we're sufficiently far away from the surface, count as escaping.
    if (kMaxThreshold < distance) {
      return false;
    }
  }
}

Xerophyte fucked around with this message at 15:04 on Oct 28, 2017

void sdf(float3 p, float* sdf, float3* normal) {
  float3 sphere_to_point       = p - m_center;
  float  distance_from_center  = length(sphere_to_point);

  *sdf    = distance_from_center - m_radius;
  *normal = sphere_to_point / distance_from_center;
}

// Compute the gradient of a distance field by using the forward difference. This is cheap but can 
// have issues with floating point precision since you need a small EPSILON. Using a central
// difference is more accurate, but then you need to compute the SDF 6 times instead of 3 times.
float3 normalized_gradient(SDF sdf, float3 p, float sdf_at_p) {
  const float EPSILON = 1e-5f;
  float3      gradient =
      float3(sdf(float3(p.x + EPSILON, p.y, p.z)) - sdf_at_p,
             sdf(float3(p.x, p.y + EPSILON, p.z)) - sdf_at_p,
             sdf(float3(p.x, p.y, p.z + EPSILON)) - sdf_at_p);
  return gradient / length(gradient);
}

Xerophyte fucked around with this message at 07:22 on Oct 30, 2017

lord funk fucked around with this message at 17:37 on Nov 16, 2017