Function createCullingVolume

CesiumGeometry/src/CullingVolume.cpp:17–80

namespace CesiumGeometry {

CullingVolume createCullingVolume(
    const glm::dvec3& position,
    const glm::dvec3& direction,
    const glm::dvec3& up,
    const double fovx,
    const double fovy) noexcept {
  const double t = glm::tan(0.5 * fovy);
  const double b = -t;
  const double r = glm::tan(0.5 * fovx);
  const double l = -r;

  const double positionLen = glm::length(position);
  const double n = std::max(
      1.0,
      std::nextafter(positionLen, std::numeric_limits<double>::max()) -
          positionLen);

  // TODO: this is all ported directly from CesiumJS, can probably be refactored
  // to be more efficient with GLM.

  const glm::dvec3 right = glm::cross(direction, up);

  glm::dvec3 nearCenter = direction * n;
  nearCenter = position + nearCenter;

  // Left plane computation
  glm::dvec3 normal = right * l;
  normal = nearCenter + normal;
  normal = normal - position;
  normal = glm::normalize(normal);
  normal = glm::cross(normal, up);
  normal = glm::normalize(normal);

  const CesiumGeometry::Plane leftPlane(normal, -glm::dot(normal, position));

  // Right plane computation
  normal = right * r;
  normal = nearCenter + normal;
  normal = normal - position;
  normal = glm::cross(up, normal);
  normal = glm::normalize(normal);

  const CesiumGeometry::Plane rightPlane(normal, -glm::dot(normal, position));

  // Bottom plane computation
  normal = up * b;
  normal = nearCenter + normal;
  normal = normal - position;
  normal = glm::cross(right, normal);
  normal = glm::normalize(normal);

  const CesiumGeometry::Plane bottomPlane(normal, -glm::dot(normal, position));

  // Top plane computation
  normal = up * t;
  normal = nearCenter + normal;
  normal = normal - position;
  normal = glm::cross(normal, right);