CurvedEarthPositionComponent.cpp

#include <limits>
#include <glm/gtx/quaternion.hpp>
#include "CurvedEarthPositionComponent.h"
#include "Components/Core/TransformComponent.h"
 
#include "Types.h"
 
using namespace Cogs::Reflection;
 
void Cogs::Core::CurvedEarthPositionComponent::registerType()
{
  Field fields[] = {
    Field(Name("position"), &CurvedEarthPositionComponent::position)
  };
  Method methods[] = {
    Method(Name("update"), &CurvedEarthPositionComponent::update)
  };
 
  DynamicComponent::registerDerivedType<CurvedEarthPositionComponent>().setMethods(methods).setFields(fields);
}
 
 
void Cogs::Core::CurvedEarthPositionComponent::update()
{
  const float R = 6371000.f;
 
  if (!hasChanged()) return;
 
  auto * trComp = getComponent<TransformComponent>();
 
  float d = glm::length(glm::vec2(position));
 
  trComp->position = glm::vec3(position.x,
                               position.y,
                               position.z - (R - glm::sqrt((R - d)*(R + d))));
  const glm::vec3 a = glm::vec3(0, 0, 1);
  const glm::vec3 b = glm::normalize(trComp->position - glm::vec3(0, 0, -R));
  const glm::vec3 n = glm::cross(a, b);
  const float n_l = glm::length(n);
  if (std::numeric_limits<float>::epsilon() < glm::abs(n_l)) {
    trComp->rotation = glm::angleAxis(glm::acos(glm::dot(a, b)), (1.f / n_l)*n);
  }
  else {
    trComp->rotation = glm::quat();
  }
  trComp->setChanged();
}