sparkler: introduce a particle system

A while ago I made this particle system on SDL, and had the beginnings of
an octree implemented within it, but never finished actually using the
octree to accelerate the proximity searches.

This now has the octree completed and of course more particle interactions now
that neighbors could be found more quickly.

The simulation somewhat resembles a fireworks display.  Every particle is drawn
as a single pixel.  The visual effect is dominated by spontaneously spawned
rockets which explode into thousands of particles accompanied by bursts that
thrust particles away from the explosion radially in an expanding sphere
resembling a shock wave.  When the shock wave happens to strike another rocket,
it explodes, resulting in another shock wave.  This can produce spectacular
chain reactions, so it's worth running for some time and seeing what transpires.

1 files changed, 338 insertions, 0 deletions

diff --git a/modules/sparkler/particles.c b/modules/sparkler/particles.c
new file mode 100644
index 0000000..ee23972
--- /dev/null
+++ b/modules/sparkler/particles.c
@@ -0,0 +1,338 @@
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <math.h>
+#include <stdlib.h>
+#include <time.h>
+
+#include "fb.h"
+
+#include "chunker.h"
+#include "container.h"
+#include "bsp.h"
+#include "list.h"
+#include "particle.h"
+#include "particles.h"
+#include "v3f.h"
+
+#define ZCONST	0.4f
+
+/* private particle with all the particles bookkeeping... */
+typedef struct _particle_t {
+	list_head_t		siblings;	/* sibling particles */
+	list_head_t		children;	/* children particles */
+
+	particle_props_t	props;		/* we reference this in the public particle, I might change
+						 * the way props are allocated so coding everything to use a
+						 * reference for now.  It may make sense to have props allocated
+						 * separately via their own chunker, and perform some mass operations
+						 * against the list of chunks rather than chasing the pointers of
+						 * the particle heirarchy. TODO
+						 */
+	particle_t		public;		/* the public particle_t is embedded */
+
+	uint8_t			context[];	/* particle type-specific context [public.ops.context_size] */
+} _particle_t;
+
+struct particles_t {
+	chunker_t		*chunker;	/* chunker for variably-sized particle allocation (includes context) */
+	list_head_t		active;		/* top-level active list of particles heirarchy */
+	bsp_t			*bsp;		/* bsp spatial index of the particles */
+};
+
+
+/* create a new particle system */
+particles_t * particles_new(void)
+{
+	particles_t	*particles;
+
+	particles = calloc(1, sizeof(particles_t));
+	if (!particles) {
+		return NULL;
+	}
+
+	particles->chunker = chunker_new(sizeof(_particle_t) * 128);
+	if (!particles->chunker) {
+		return NULL;
+	}
+
+	particles->bsp = bsp_new();
+	if (!particles->bsp) {
+		return NULL;
+	}
+
+	INIT_LIST_HEAD(&particles->active);
+
+	return particles;
+}
+
+
+/* TODO: add a public interface for destroying particles?  for now we just return PARTICLE_DEAD in the sim */
+static inline void _particles_free_particle(particles_t *particles, _particle_t *p)
+{
+	assert(p);
+
+	particle_cleanup(particles, &p->public);
+	chunker_free(p);
+}
+
+
+static inline void _particles_free(particles_t *particles, list_head_t *list)
+{
+	_particle_t	*p, *_p;
+
+	assert(particles);
+	assert(list);
+
+	list_for_each_entry_safe(p, _p, list, siblings) {
+		_particles_free(particles, &p->children);
+		_particles_free_particle(particles, p);
+	}
+}
+
+
+/* free up all the particles */
+void particles_free(particles_t *particles)
+{
+	assert(particles);
+
+	_particles_free(particles, &particles->active);
+}
+
+
+/* reclaim a dead particle, moving it to the free list */
+static void particles_reap_particle(particles_t *particles, _particle_t *particle)
+{
+	assert(particles);
+	assert(particle);
+
+	if (!list_empty(&particle->children)) {
+		/* adopt any orphaned children using the global parts list */
+		list_splice(&particle->children, &particles->active);
+	}
+
+	list_del(&particle->siblings);
+	bsp_delete_occupant(particles->bsp, &particle->public.occupant);
+	_particles_free_particle(particles, particle);
+}
+
+
+/* add a particle to the specified list */
+static inline int _particles_add_particle(particles_t *particles, list_head_t *list, particle_props_t *props, particle_ops_t *ops)
+{
+	_particle_t	*p;
+
+	assert(particles);
+	assert(ops);
+	assert(list);
+
+	p = chunker_alloc(particles->chunker, sizeof(_particle_t) + ops->context_size);
+	if (!p) {
+		return 0;
+	}
+
+	INIT_LIST_HEAD(&p->children);
+	INIT_LIST_HEAD(&p->siblings);
+
+	/* inherit the parent's properties and ops if they're not explicitly provided */
+	if (props) {
+		p->props = *props;
+	} else {
+		p->props.of_use = 0;
+	}
+
+	p->public.props = &p->props;
+	p->public.ops = ops;
+
+	if (ops->context_size) {
+		p->public.ctxt = p->context;
+	}
+
+	if (!particle_init(particles, &p->public)) {
+		/* XXX FIXME this shouldn't be normal, we don't want to allocate
+		 * particles that cannot be initialized.  the rockets today set a cap
+		 * by failing initialization, that's silly. */
+		chunker_free(p);
+		return 0;
+	}
+
+	p->public.props->of_use = 1;
+	list_add(&p->siblings, list);
+	bsp_add_occupant(particles->bsp, &p->public.occupant, &p->props.position);
+
+	return 1;
+}
+
+
+/* add a new "top-level" particle of the specified props and ops taking from the provided parts list */
+int particles_add_particle(particles_t *particles, particle_props_t *props, particle_ops_t *ops)
+{
+	assert(particles);
+
+	return _particles_add_particle(particles, &particles->active, props, ops);
+}
+
+
+/* spawn a new child particle from a parent, initializing it via inheritance if desired */
+void particles_spawn_particle(particles_t *particles, particle_t *parent, particle_props_t *props, particle_ops_t *ops)
+{
+	_particle_t	*p = container_of(parent, _particle_t, public);
+
+	assert(particles);
+	assert(parent);
+
+	_particles_add_particle(particles, &p->children, props ? props : parent->props, ops ? ops : parent->ops);
+}
+
+
+/* plural version of particle_add(); adds multiple "top-level" particles of uniform props and ops */
+void particles_add_particles(particles_t *particles, particle_props_t *props, particle_ops_t *ops, int num)
+{
+	int	i;
+
+	assert(particles);
+
+	for (i = 0; i < num; i++) {
+		_particles_add_particle(particles, &particles->active, props, ops);
+	}
+}
+
+
+/* Simple accessor to get the bsp pointer, the bsp is special because we don't want to do
+ * callbacks per-occupant, so the bsp_occupant_t and search functions are used directly by
+ * the per-particle code needing nearest-neighbor search.  that requires an accessor since
+ * particles_t is opaque.  This seemed less shitty than opening up particles_t.
+ */
+bsp_t * particles_bsp(particles_t *particles)
+{
+	assert(particles);
+	assert(particles->bsp);
+
+	return particles->bsp;
+}
+
+
+static inline void _particles_draw(particles_t *particles, list_head_t *list, fb_fragment_t *fragment)
+{
+	float		w2 = fragment->width / 2, h2 = fragment->height / 2;
+	_particle_t	*p;
+
+	assert(particles);
+	assert(list);
+	assert(fragment);
+
+	list_for_each_entry(p, list, siblings) {
+		int	x, y;
+
+		/* project the 3d coordinates onto the 2d plane */
+		x = ((float)(p->props.position.x / (p->props.position.z - ZCONST)) * w2) + w2;
+		y = ((float)(p->props.position.y / (p->props.position.z - ZCONST)) * h2) + h2;
+
+		particle_draw(particles, &p->public, x, y, fragment);
+		_particles_draw(particles, &p->children, fragment);
+	}
+}
+
+
+/* draw all of the particles, currently called in heirarchical order */
+void particles_draw(particles_t *particles, fb_fragment_t *fragment)
+{
+	assert(particles);
+
+	_particles_draw(particles, &particles->active, fragment);
+}
+
+
+static inline particle_status_t _particles_sim(particles_t *particles, list_head_t *list)
+{
+	particle_status_t	ret = PARTICLE_DEAD, s;
+	_particle_t		*p, *_p;
+
+	assert(particles);
+	assert(list);
+
+	list_for_each_entry_safe(p, _p, list, siblings) {
+		if ((s = particle_sim(particles, &p->public)) == PARTICLE_ALIVE) {
+			ret = PARTICLE_ALIVE;
+
+			if (_particles_sim(particles, &p->children) == PARTICLE_ALIVE) {
+				ret = PARTICLE_ALIVE;
+			}
+		} else {
+			particles_reap_particle(particles, p);
+		}
+	}
+
+	return ret;
+}
+
+
+/* simulate the particles, call the sim method of every particle in the heirarchy, this is what makes the particles dynamic */
+/* if any paticle is still living, we return PARTICLE_ALIVE, to inform the caller when everything's dead */
+particle_status_t particles_sim(particles_t *particles)
+{
+	assert(particles);
+
+	return _particles_sim(particles, &particles->active);
+}
+
+
+static inline void _particles_age(particles_t *particles, list_head_t *list)
+{
+	_particle_t	*p;
+
+	assert(particles);
+	assert(list);
+
+	/* TODO: since this *only* involves the properties struct, if they were
+	 * allocated from a separate slab containing only properties, it'd be
+	 * more efficient to iterate across property arrays and skip inactive
+	 * entries.  This heirarchical pointer-chasing recursion isn't
+	 * particularly good for cache utilization.
+	 */
+	list_for_each_entry(p, list, siblings) {
+#if 1
+		if (p->props.mass > 0.0f) {
+			/* gravity, TODO: mass isn't applied. */
+			static v3f_t	gravity = v3f_init(0.0f, -1.0f, 0.0f);
+			v3f_t		g;
+
+			g = v3f_mult_scalar(&gravity, 0.08f);
+			p->props.direction = v3f_add(&p->props.direction, &g);
+			p->props.direction = v3f_normalize(&p->props.direction);
+		}
+#endif
+
+#if 1
+		/* some drag/resistance proportional to velocity TODO: integrate mass */
+		if (p->props.velocity > 0.0f) {
+			p->props.velocity -= ((p->props.velocity * p->props.velocity * p->props.drag));
+			if (p->props.velocity < 0.0f) {
+				p->props.velocity = 0;
+			}
+		}
+#endif
+
+		/* regular movement */
+		if (p->props.velocity > 0.0f) {
+			v3f_t	movement = v3f_mult_scalar(&p->props.direction, p->props.velocity);
+
+			p->props.position = v3f_add(&p->props.position, &movement);
+			bsp_move_occupant(particles->bsp, &p->public.occupant, &p->props.position);
+		}
+
+		_particles_age(particles, &p->children);
+	}
+}
+
+
+/* advance time for all the particles (move them), this doesn't currently invoke any part-specific helpers, it's just applying
+ * physics-type stuff, moving particles according to their velocities, directions, mass, drag, gravity etc... */
+void particles_age(particles_t *particles)
+{
+	assert(particles);
+
+	_particles_age(particles, &particles->active);
+}