asteroids/asteroids.c

#include "asteroids.h"

#include "collisions.h"
#include "entity.h"
#include "renderer.h"
#include "rng.h"
#include "scene.h"

#include <assert.h>
#include <math.h>
#include <string.h>

#define MIN_VERTS 5
#define VERT_RANGE (MAX_VERTS - MIN_VERTS)
#define A_JITTER 0.8
#define V_JITTER 0.0005
#define ROT_JITTER 0.005
#define R_JITTER 0.01
#define MIN_DIST 0.8

#define REPLACE_MIN 3
#define REPLACE_MAX 5
#define REPLACE_RANGE (REPLACE_MAX - REPLACE_MIN)
#define REPLACE_R_COEFF 0.8
#define REPLACE_R_JITTER 0.02
#define REPLACE_A_JITTER 0.4
#define REPLACE_V_JITTER 0.0005
#define REPLACE_RADIAL_V_COEFF 0.005
#define REPLACE_ROT_JITTER 0.02

#define COLLIDE_PRIOR 0

typedef struct {
	bool valid;
	unsigned component_id;
	asteroid_size_t size;
} entry_t;

static asteroids_cb_t clear;
static unsigned count;
static entry_t entries[MAX_ENTITIES];

static float radii[] = {
	[ASTEROID_SMALL] = 0.025f,
	[ASTEROID_MEDIUM] = 0.05f,
	[ASTEROID_LARGE] = 0.1f,
	[ASTEROID_HUGE] = 0.2f,
};

static void update(unsigned new_entity_id, void *ref)
{
	entry_t *old_e = (entry_t *)ref;
	entry_t *new_e = entries + new_entity_id;
	memcpy(new_e, old_e, sizeof(entry_t));
	old_e->valid = false;
	entity_update_component(new_entity_id, new_e->component_id, new_e);
}

static void remove(void *ref)
{
	entry_t *e = (entry_t *)ref;
	e->valid = false;
	--count;
	if (count == 0)
		clear();
}

static void
create_asteroid(vec2_t pos, vec2_t vel, float rot, asteroid_size_t size)
{
	const float r_mean = radii[size];
	const unsigned n = MIN_VERTS + rng_uint32() % VERT_RANGE;

	const float da = 2.0f * PI / n;
	vec2_t verts[n];
	for (unsigned i = 0; i < n; ++i) {
		const float r = r_mean + rng_plusminus() * R_JITTER;
		const float a_jitter = A_JITTER * rng_plusminus() * da / 2;
		const float a = i * da + a_jitter;
		verts[i] = (vec2_t) { r * cosf(a), r * sinf(a) };
	}

	const unsigned id = entity_add();
	scene_add(id, verts, n, true);
	physics_add(id, pos, MAT2_ID, vel, rot, r_mean * r_mean);
	collisions_add(id, r_mean, COLLIDE_PRIOR, physics_bounce);

	entry_t *entry = entries + id;
	entry->valid = true;
	entry->component_id = entity_add_component(id, update, remove, entry);
	entry->size = size;

	++count;
}

static asteroid_size_t draw_size(const asteroid_size_dist_entry_t *dist)
{
	const float r = rng_canon();
	float acc = 0;
	for (unsigned i = 0; dist[i].probability != 0.0f; ++i) {
		acc += dist[i].probability;
		if (r < acc)
			return dist[i].size;
	}
	assert(false);
}

void asteroids_clear()
{
	count = 0;
	memset(entries, 0, sizeof(entries));
}

void asteroids_on_clear(asteroids_cb_t cb)
{
	clear = cb;
}

void asteroids_add(const asteroid_size_dist_entry_t *dist)
{
	vec2_t pos;
	do {
		pos.y = rng_plusminus();
		pos.x = aspect * rng_plusminus();
	} while (vec2_len(pos) < MIN_DIST);
	const vec2_t vel = {
		V_JITTER * rng_plusminus(),
		V_JITTER * rng_plusminus(),
	};
	const float rot = ROT_JITTER * rng_plusminus();
	const asteroid_size_t size = draw_size(dist);

	create_asteroid(pos, vel, rot, size);
}

void asteroids_hit(unsigned shot, unsigned asteroid, physics_sep_t)
{
	assert(entries[asteroid].valid);
	entity_mark(asteroid);

	const asteroid_size_t old_size = entries[asteroid].size;
	if (old_size == ASTEROID_SMALL)
		return;
	const asteroid_size_t size = old_size - 1;
	const float mass = radii[size] * radii[size];

	const physics_t *phys_shot = physics_get(shot);
	const physics_t *phys_ast = physics_get(asteroid);
	const vec2_t p_shot = vec2_scale(phys_shot->vel, phys_shot->mass);
	const vec2_t p_ast = vec2_scale(phys_ast->vel, phys_ast->mass);

	const unsigned n = REPLACE_MIN + rng_uint32() % REPLACE_RANGE;
	const float da = 2 * PI / n;

	const vec2_t p = vec2_add(p_shot, p_ast);
	const vec2_t inherit_v = vec2_scale(p, 1 / (n * mass));

	for (unsigned i = 0; i < n; ++i) {
		const float r = REPLACE_R_COEFF * radii[old_size]
		    + REPLACE_R_JITTER * rng_plusminus();
		const float a = i * da + REPLACE_A_JITTER * rng_plusminus();
		const vec2_t disp = { r * cosf(a), r * sinf(a) };

		const vec2_t radial_v = vec2_scale(
		    vec2_norm(disp), REPLACE_RADIAL_V_COEFF * rng_canon());
		const vec2_t jitter_v = {
			REPLACE_V_JITTER * rng_plusminus(),
			REPLACE_V_JITTER * rng_plusminus(),
		};

		const vec2_t pos = vec2_add(phys_ast->pos, disp);
		const vec2_t vel = vec2_add(inherit_v, vec2_add(radial_v, jitter_v));
		const float rot
		    = phys_ast->rot / n + REPLACE_ROT_JITTER * rng_plusminus();

		create_asteroid(pos, vel, rot, size);
	}
}

bool asteroids_check(unsigned id)
{
	return entries[id].valid;
}