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, 113 insertions, 0 deletions

diff --git a/modules/sparkler/simple.c b/modules/sparkler/simple.c
new file mode 100644
index 0000000..e453e46
--- /dev/null
+++ b/modules/sparkler/simple.c
@@ -0,0 +1,113 @@
+#include <stdlib.h>
+
+#include "draw.h"
+#include "particle.h"
+#include "particles.h"
+
+
+/* a "simple" particle type */
+#define SIMPLE_MAX_DECAY_RATE	20
+#define SIMPLE_MIN_DECAY_RATE	2
+#define SIMPLE_MAX_LIFETIME	110
+#define SIMPLE_MIN_LIFETIME	30
+#define SIMPLE_MAX_SPAWN	15
+#define SIMPLE_MIN_SPAWN	2
+
+extern particle_ops_t rocket_ops;
+
+typedef struct _simple_ctxt_t {
+	int		decay_rate;
+	int		longevity;
+	int		lifetime;
+} simple_ctxt_t;
+
+
+static int simple_init(particles_t *particles, particle_t *p)
+{
+	simple_ctxt_t	*ctxt = p->ctxt;
+
+	ctxt->decay_rate = rand_within_range(SIMPLE_MIN_DECAY_RATE, SIMPLE_MAX_DECAY_RATE);
+	ctxt->lifetime = ctxt->longevity = rand_within_range(SIMPLE_MIN_LIFETIME, SIMPLE_MAX_LIFETIME);
+
+	if (!p->props->of_use) {
+		/* everything starts from the bottom center */
+		p->props->position.x = 0;
+		p->props->position.y = 0;
+		p->props->position.z = 0;
+
+		/* TODO: direction random-ish within the range of a narrow upward facing cone */
+		p->props->direction.x = (float)(rand_within_range(0, 6) - 3) * .1f;
+		p->props->direction.y = 1.0f + (float)(rand_within_range(0, 6) - 3) * .1f;
+		p->props->direction.z = (float)(rand_within_range(0, 6) - 3) * .1f;
+		p->props->direction = v3f_normalize(&p->props->direction);
+
+		p->props->velocity = (float)rand_within_range(300, 800) / 100000.0;
+
+		p->props->drag = 0.03;
+		p->props->mass = 0.3;
+		p->props->of_use = 1;
+	} /* else { we've been given properties, manipulate them or run with them? } */
+
+	return 1;
+}
+
+
+static particle_status_t simple_sim(particles_t *particles, particle_t *p)
+{
+	simple_ctxt_t	*ctxt = p->ctxt;
+
+	/* a particle is free to manipulate its children list when aging, but not itself or its siblings */
+	/* return PARTICLE_DEAD to remove kill yourself, do not age children here, the age pass will recurse
+	 * into children and age them independently _after_ their parents have been aged
+	 */
+	if (!ctxt->longevity || (ctxt->longevity -= ctxt->decay_rate) <= 0) {
+		ctxt->longevity = 0;
+		return PARTICLE_DEAD;
+	}
+
+	/* create particles inheriting our type based on some silly conditions, with some tweaks to their direction */
+	if (ctxt->longevity == 42 || (ctxt->longevity > 500 && !(ctxt->longevity % 50))) {
+		int	i, num = rand_within_range(SIMPLE_MIN_SPAWN, SIMPLE_MAX_SPAWN);
+
+		for (i = 0; i < num; i++) {
+			particle_props_t	props = *p->props;
+			particle_ops_t		*ops = INHERIT_OPS;
+
+			if (i == (SIMPLE_MAX_SPAWN - 2)) {
+				ops = &rocket_ops;
+				props.velocity = (float)rand_within_range(60, 100) / 1000000.0;
+			} else {
+				props.velocity = (float)rand_within_range(30, 100) / 10000.0;
+			}
+
+			props.direction.x += (float)(rand_within_range(0, 315 * 2) - 315) / 100.0;
+			props.direction.y += (float)(rand_within_range(0, 315 * 2) - 315) / 100.0;
+			props.direction.z += (float)(rand_within_range(0, 315 * 2) - 315) / 100.0;
+			props.direction = v3f_normalize(&props.direction);
+
+			particles_spawn_particle(particles, p, &props, ops); // XXX
+		}
+	}
+
+	return PARTICLE_ALIVE;
+}
+
+
+static void simple_draw(particles_t *particles, particle_t *p, int x, int y, fb_fragment_t *f)
+{
+	simple_ctxt_t	*ctxt = p->ctxt;
+
+	if (!draw_pixel(f, x, y, makergb(0xff, 0xff, 0xff, ((float)ctxt->longevity / ctxt->lifetime)))) {
+		/* immediately kill off stars that wander off screen */
+		ctxt->longevity = 0;
+	}
+}
+
+
+particle_ops_t	simple_ops = {
+			.context_size = sizeof(simple_ctxt_t),
+			.sim = simple_sim,
+			.init = simple_init,
+			.draw = simple_draw,
+			.cleanup = NULL,
+		};