nbody.h

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#ifndef NBODY_H
#define NBODY_H
 
#include "sphere_types.h"
#include <cglm/types.h>
#include <stdbool.h>
 
enum { NBODY_MAX_BODIES = 32 };
 
static const float NBODY_DEFAULT_G = 1.0F;
 
static const float NBODY_SOFTENING_SQ = 0.25F;
 
static const float NBODY_SOFTENING_FACTOR = 2.0F;
 
static const float NBODY_FIXED_DT = 1.0F / 120.0F;
 
static const float NBODY_MAX_ACCUMULATOR = 1.0F / 10.0F;
 
static const float NBODY_CONFINEMENT_RADIUS = 25.0F;
 
static const float NBODY_CONFINEMENT_K = 5.0F;
 
static const float NBODY_CONFINEMENT_DAMPING = 20.0F;
 
typedef struct {
    double position[3]; 
    double mass;        
    double velocity[3]; 
    float radius;       
    vec3 albedo;        
    float metallic;     
    float roughness;    
    double prev_position[3]; 
} NBodyParticle;
 
static const float NBODY_TIME_SCALE_RATE = 3.0F;
 
typedef struct {
    vec3 position;  
    vec3 color;     
    float velocity; 
    bool active;    
} NBodyImpact;
 
typedef struct NBodySim {
    NBodyParticle bodies[NBODY_MAX_BODIES]; 
    int body_count;                         
    float gravity;           
    float accumulator;       
    float time_scale;        
    float target_time_scale; 
    float initial_energy;    
    float sim_time;          
    bool paused;             
    /* Confinement impact events — one slot per body, cleared each frame.
     * Only the peak velocity across integration sub-steps is kept. */
    NBodyImpact impacts[NBODY_MAX_BODIES]; 
} NBodySim;
 
void nbody_init_preset(NBodySim* sim);
 
void nbody_step(NBodySim* sim, float delta_time);
 
void nbody_write_instances(const NBodySim* sim, SphereInstance* out);
 
int nbody_get_count(const NBodySim* sim);
 
float nbody_total_energy(const NBodySim* sim);
 
float nbody_kinetic_energy(const NBodySim* sim);
 
float nbody_energy_drift(const NBodySim* sim);
 
float nbody_energy_drift_signed(const NBodySim* sim);
 
void nbody_update_time_scale(NBodySim* sim, float delta_time);
 
#endif /* NBODY_H */