atmosphere.h

#pragma once
 
#include <glm/glm.hpp>
 
namespace Vkm::Engine {
 
struct SkySettings;
 
} // namespace Vkm::Engine
 
namespace Vkm::Engine::Atmosphere {
 
// The procedural sky's atmosphere: an Earth-like planet under Rayleigh and Mie
// layers, in metres. The one statement of it: the GPU sky bake (`shaders/ibl/sky`,
// geometry via `GLBackend::shaderConstants`) and `sunTransmittance` on the CPU both
// read it, so sky and sunlight agree.
 
constexpr float PLANET_RADIUS = 6371000.0f;  
constexpr float TOP_RADIUS    = 6471000.0f;  
constexpr float EYE_ALTITUDE  = 1000.0f;     

inline const glm::vec3 RAYLEIGH_SCATTERING = {5.802e-6f, 13.558e-6f, 33.1e-6f};
constexpr float RAYLEIGH_SCALE_HEIGHT = 8000.0f;
 
constexpr float MIE_SCATTERING   = 21.0e-6f;  
constexpr float MIE_EXTINCTION   = 1.1f;      
constexpr float MIE_SCALE_HEIGHT = 1200.0f;

struct Coefficients {
    glm::vec3 rayleighScattering;  
    glm::vec3 mieScattering;
    glm::vec3 mieExtinction;       
};

Coefficients coefficients(const SkySettings& sky);

glm::vec3 sunTransmittance(const SkySettings& sky);

glm::vec3 sunlight(const SkySettings& sky);
 
} // namespace Vkm::Engine::Atmosphere