Make shots self-destruct after 4 seconds

build.sh

@@ -9,4 +9,5 @@ defs="-D_POSIX_C_SOURCE=200809L"
 $cc $warn $flags $libs $defs \
 	-o asteroids \
 	asteroids.c collisions.c entity.c fb.c game.c input.c \
-	main.c maths.c physics.c scene.c renderer.c rng.c text.c
+	main.c maths.c physics.c scene.c renderer.c rng.c \
+	self_destruct.c text.c

game.c

@@ -8,6 +8,7 @@
 #include "renderer.h"
 #include "rng.h"
 #include "scene.h"
+#include "self_destruct.h"
 #include "text.h"
 
 #include <assert.h>
@@ -15,6 +16,8 @@
 #include <math.h>
 #include <string.h>
 
+#define FPS 60
+
 #define INIT_LEVEL 1
 
 #define SHIP_COLLIDE_R 0.025
@@ -28,6 +31,7 @@
 #define SHOT_VEL 0.03
 #define SHOT_COLLIDE_R 0.015
 #define SHOT_MASS 0.00025
+#define SHOT_LIFETIME_S 4
 
 #define ARROW_SCALE 0.0125
 #define ARROW_WIDTH 4
@@ -174,6 +178,7 @@ static void shoot()
 	scene_add(id, shot_verts, NELEMS(shot_verts), false);
 	physics_add(id, pos, ship->dir, vel, 0, SHOT_MASS);
 	collisions_add(id, SHOT_COLLIDE_R, SHOT_COLLIDE_PRIOR, shot_collide);
+	self_destruct_add(id, FPS * SHOT_LIFETIME_S);
 
 	const vec2_t p_ship = vec2_scale(ship->vel, ship->mass);
 	const vec2_t p_shot = vec2_scale(vel, SHOT_MASS);
@@ -213,6 +218,7 @@ static void create_field()
 	scene_clear();
 	physics_init();
 	collisions_init();
+	self_destruct_clear();
 
 	ship_entity_id = entity_add();
 	scene_add(ship_entity_id, ship_verts, NELEMS(ship_verts), true);
@@ -309,6 +315,7 @@ void game_update()
 
 	ship_update();
 	physics_update();
+	self_destruct_update();
 	collisions_update();
 	scene_update();
 
@@ -317,7 +324,7 @@ void game_update()
 	const bool items_enabled
 	    = !clear && score >= ITEM_MIN_SCORE && armour_level < 9;
 	if (items_enabled && !item
-	    && rng_canon() < 1.0f / (60 * ITEM_SPAWN_EXP_S))
+	    && rng_canon() < 1.0f / (FPS * ITEM_SPAWN_EXP_S))
 		add_item();
 }
 

self_destruct.c

@@ -0,0 +1,60 @@
+#include "self_destruct.h"
+
+#include "entity.h"
+
+#include <assert.h>
+#include <string.h>
+
+#define MAX 256U
+
+typedef struct {
+	unsigned entity_id;
+	unsigned component_id;
+	unsigned rem;
+} cmp_t;
+
+static unsigned count;
+static cmp_t cmps[MAX];
+
+static void update(unsigned new_entity_id, void *ref)
+{
+	cmp_t *c = (cmp_t *)ref;
+	c->entity_id = new_entity_id;
+}
+
+static void remove(void *ref)
+{
+	cmp_t *c = (cmp_t *)ref;
+	const cmp_t *last = cmps + (count - 1);
+	if (c < last) {
+		memcpy(c, last, sizeof(cmp_t));
+		entity_update_component(c->entity_id, c->component_id, c);
+	}
+	--count;
+}
+
+void self_destruct_clear()
+{
+	count = 0;
+}
+
+void self_destruct_update()
+{
+	for (unsigned i = 0; i < count; ++i) {
+		if (cmps[i].rem == 0)
+			entity_mark(cmps[i].entity_id);
+		else
+			--cmps[i].rem;
+	}
+}
+
+void self_destruct_add(unsigned id, unsigned frames)
+{
+	assert(count < MAX);
+	cmp_t *c = cmps + count++;
+	*c = (cmp_t) {
+		.entity_id = id,
+		.rem = frames,
+		.component_id = entity_add_component(id, update, remove, c),
+	};
+}

self_destruct.h

@@ -0,0 +1,8 @@
+#ifndef SELF_DESTRUCT_H
+#define SELF_DESTRUCT_H
+
+void self_destruct_clear();
+void self_destruct_update();
+void self_destruct_add(unsigned id, unsigned frames);
+
+#endif