#define BBOX_UNIT (bbox_t){{-0.5f, -0.5f, -0.5f}, {0.5f, 0.5f, 0.5f}}
#define BBOX_ZERO (bbox_t){V3_ZERO, V3_ZERO}

typedef struct {
    v3 start;
    v3 end;
} bbox_t;

#define ENTITY_COLLIDE	(1)
#define ENTITY_MOVE	(1 << 1)
#define ENTITY_ALPHA	(1 << 2)

typedef struct {
    u32		flags;

    model_t		model;

    v3		position;
    v3		velocity;
    bbox_t		bbox;
} entity_t;

#define MAX_ENTITIES 4

typedef struct enode_t {
    i32		id;
    entity_t	entity;
    struct enode_t	*next;
    struct enode_t	*prev;
} enode_t;

typedef struct {
    i32		count;
    enode_t		nodes[MAX_ENTITIES];
    struct enode_t	*first;
    struct enode_t	*last;
} elist_t;

typedef enum {ui_list, ui_stack} ui_layout_enum;

typedef struct {
    prge_window_t	window;
    input_t		input;
    shader_t	shader;
    rect_t		rect;
    ui_layout_enum	layout;
    v2		last;
    arena_t		*arena;
    f32		padding;
} ui_t;