#ifndef WORLD_PHYSICS_H
#define WORLD_PHYSICS_H

/*
 * Simple game physics:
 *   gravity, terrain contact, oriented-box collisions (separating axes)
 *   per collider pair, walkable slopes, step-up for characters,
 *   stepping over low things (slowing down for them), pushing by
 *   weight/strength (walking only shoves light things aside), and friction.
 *   Nothing comes to rest on people: it slides off them, and whatever hits
 *   them adds to their knock (momentum), which may stagger or floor them.
 */

#include "world/object.h"
#include "world/terrain.h"

/* Something low and narrow enough to step over: its height (0 = not that). */
float Physics_lowObstacle(const Object *o);
/* Solid enough to stand on and won't break (heavy or fixed, a flat top; not a bottle or a table). */
bool  Physics_standsOn(const struct Object *o);
/* How wide the top of o is to stand on, the narrow way (m; a log: about its diameter). */
float Physics_footing(const Object *o);
/* Is o something low that who steps over (no collision with the body)? */
bool Physics_stepsOver(const Object *who, const Object *o);

/* Do collider ia of a and collider ib of b overlap? */
bool Physics_overlap(const Object *a, int ia, const Object *b, int ib);

/* How deep a and b are in each other (deepest collider pair; 0 = apart). */
float Physics_penetration(const Object *a, const Object *b);

/* Advances one dynamic object and resolves its contacts. */
void Physics_step(Object *obj, Object *const *objects, int count, const Terrain *terrain, float dt);
/* Where things are (the world's cell grid), so a step only looks at what's near; NULL: everything. */
struct Grid;
void Physics_useGrid(struct Grid *grid);

#endif /* WORLD_PHYSICS_H */