meta2d: add a classic 2D metaballs module

1 files changed, 235 insertions, 0 deletions

diff --git a/src/modules/meta2d/meta2d.c b/src/modules/meta2d/meta2d.c
new file mode 100644
index 0000000..08cd15a
--- /dev/null
+++ b/src/modules/meta2d/meta2d.c
@@ -0,0 +1,235 @@
+/*
+ *  Copyright (C) 2019 - Vito Caputo - <vcaputo@pengaru.com>
+ *
+ *  This program is free software: you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License version 3 as published
+ *  by the Free Software Foundation.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/* https://en.wikipedia.org/wiki/Metaballs */
+
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "din/din.h"
+#include "fb.h"
+#include "rototiller.h"
+
+#include "v2f.h"
+#include "v3f.h"
+
+#define	META2D_NUM_BALLS	10
+
+typedef struct meta2d_ball_t {
+	v2f_t		position;
+	float		radius;
+	v3f_t		color;
+} meta2d_ball_t;
+
+typedef struct meta2d_context_t {
+	unsigned	n;
+	din_t		*din_a, *din_b;
+	float		din_t;
+	unsigned	n_cpus;
+	meta2d_ball_t	balls[META2D_NUM_BALLS];
+} meta2d_context_t;
+
+
+/* convert a color into a packed, 32-bit rgb pixel value (taken from libs/ray/ray_color.h) */
+static inline uint32_t color_to_uint32(v3f_t color) {
+	uint32_t	pixel;
+
+	if (color.x > 1.0f) color.x = 1.0f;
+	if (color.y > 1.0f) color.y = 1.0f;
+	if (color.z > 1.0f) color.z = 1.0f;
+
+	if (color.x < .0f) color.x = .0f;
+	if (color.y < .0f) color.y = .0f;
+	if (color.z < .0f) color.z = .0f;
+
+	pixel = (uint32_t)(color.x * 255.0f);
+	pixel <<= 8;
+	pixel |= (uint32_t)(color.y * 255.0f);
+	pixel <<= 8;
+	pixel |= (uint32_t)(color.z * 255.0f);
+
+	return pixel;
+}
+
+
+static void * meta2d_create_context(unsigned num_cpus)
+{
+	meta2d_context_t	*ctxt;
+
+	ctxt = calloc(1, sizeof(meta2d_context_t));
+
+	/* perlin noise is used for some organic-ish random movement of the balls */
+	ctxt->din_a = din_new(10, 10, META2D_NUM_BALLS + 2);
+	ctxt->din_b = din_new(10, 10, META2D_NUM_BALLS + 2);
+
+	srand(getpid());
+	ctxt->n_cpus = num_cpus;
+
+	for (int i = 0; i < META2D_NUM_BALLS; i++) {
+		meta2d_ball_t	*ball = &ctxt->balls[i];
+
+		v2f_rand(&ball->position, &(v2f_t){-.7f, -.7f}, &(v2f_t){.7f, .7f});
+		ball->radius = rand() / (float)RAND_MAX * .2f + .05f;
+		v3f_rand(&ball->color, &(v3f_t){0.f, 0.f, 0.f}, &(v3f_t){1.f, 1.f, 1.f});
+	}
+
+	return ctxt;
+}
+
+
+static void meta2d_destroy_context(void *context)
+{
+	meta2d_context_t	*ctxt = context;
+
+	din_free(ctxt->din_a);
+	din_free(ctxt->din_b);
+	free(ctxt);
+}
+
+
+static int meta2d_fragmenter(void *context, const fb_fragment_t *fragment, unsigned number, fb_fragment_t *res_fragment)
+{
+	meta2d_context_t	*ctxt = context;
+
+	return fb_fragment_slice_single(fragment, ctxt->n_cpus, number, res_fragment);
+}
+
+
+static void meta2d_prepare_frame(void *context, unsigned n_cpus, fb_fragment_t *fragment, rototiller_fragmenter_t *res_fragmenter)
+{
+	meta2d_context_t	*ctxt = context;
+
+	*res_fragmenter = meta2d_fragmenter;
+
+	/* move the balls around */
+	for (int i = 0; i < META2D_NUM_BALLS; i++) {
+		meta2d_ball_t	*ball = &ctxt->balls[i];
+		float		rad;
+
+		/* Perlin noise indexed by position for x,y and i for z
+		 * is used just for moving the metaballs around.
+		 *
+		 * Two noise fields are used with their values interpolated,
+		 * starting with the din_a being 100% of the movement,
+		 * with every frame migrating closer to din_b being 100%.
+		 *
+		 * Once din_b contributes 100%, it becomes din_a, and the old
+		 * din_a becomes din_b which gets randomized, and the % resets
+		 * to 0.
+		 *
+		 * This allows an organic continuous evolution of the field
+		 * over time, at double the sampling cost since we're sampling
+		 * two noise fields and interpolating them.  Since this is
+		 * just per-ball every frame, it's probably OK.  Not like it's
+		 * every pixel.
+		 */
+
+		/* ad-hoc lerp of the two dins */
+		rad = din(ctxt->din_a, &(v3f_t){
+			  .x = ball->position.x,
+			  .y = ball->position.y,
+			  .z = (float)i * (1.f / (float)META2D_NUM_BALLS)}
+			 ) * (1.f - ctxt->din_t);
+
+		rad += din(ctxt->din_b, &(v3f_t){
+			  .x = ball->position.x,
+			  .y = ball->position.y,
+			  .z = (float)i * (1.f / (float)META2D_NUM_BALLS)}
+			 ) * ctxt->din_t;
+
+		/* Perlin noise doesn't produce anything close to a uniform random distribution
+		 * of -1..+1, so it can't just be mapped directly to 2*PI with all angles getting
+		 * roughly equal occurrences in the long-run.  For now I just *10.f and it seems
+		 * to be OK.
+		 */
+		rad *= 10.f * 2.f * M_PI;
+		v2f_add(&ball->position,
+			&ball->position,
+			&(v2f_t){
+				.x = cosf(rad) * .003f,	/* small steps */
+				.y = sinf(rad) * .003f,
+			});
+
+		v2f_clamp(&ball->position,
+			  &ball->position,
+			  &(v2f_t){-.8f, -.8f},	/* keep the balls mostly on-screen */
+			  &(v2f_t){.8f, .8f}
+			);
+	}
+
+	/* when din_t reaches 1 swap a<->b, reset din_t, randomize b */
+	ctxt->din_t += .01f;
+	if (ctxt->din_t >= 1.f) {
+		din_t	*tmp;
+
+		tmp = ctxt->din_a;
+		ctxt->din_a = ctxt->din_b;
+		ctxt->din_b = tmp;
+
+		din_randomize(ctxt->din_b);
+		ctxt->din_t = 0.f;
+	}
+}
+
+
+static void meta2d_render_fragment(void *context, unsigned cpu, fb_fragment_t *fragment)
+{
+	meta2d_context_t	*ctxt = context;
+	float			xf = 2.f / (float)fragment->frame_width;
+	float			yf = 2.f / (float)fragment->frame_height;
+	v2f_t			coord;
+
+	for (int y = fragment->y; y < fragment->y + fragment->height; y++) {
+		coord.y = yf * (float)y - 1.f;
+
+		for (int x = fragment->x; x < fragment->x + fragment->width; x++) {
+			v3f_t		color = {};
+			uint32_t	pixel;
+			float		t = 0;
+
+			coord.x = xf * (float)x - 1.f;
+
+			for (int i = 0; i < META2D_NUM_BALLS; i++) {
+				meta2d_ball_t	*ball = &ctxt->balls[i];
+
+				float	f;
+
+				f = ball->radius * ball->radius / v2f_distance_sq(&coord, &ball->position);
+				v3f_add(&color, &color, v3f_mult_scalar(&(v3f_t){}, &ball->color, f));
+				t += f;
+			}
+
+			/* these thresholds define the thickness of the ribbon */
+			if (t < .7f || t > .8f)
+				color = (v3f_t){};
+
+			pixel = color_to_uint32(color);
+			fb_fragment_put_pixel_unchecked(fragment, x, y, pixel);
+		}
+	}
+}
+
+
+rototiller_module_t	meta2d_module = {
+	.create_context = meta2d_create_context,
+	.destroy_context = meta2d_destroy_context,
+	.prepare_frame = meta2d_prepare_frame,
+	.render_fragment = meta2d_render_fragment,
+	.name = "meta2d",
+	.description = "Classic 2D metaballs (threaded)",
+	.author = "Vito Caputo <vcaputo@pengaru.com>",
+	.license = "GPLv3",
+};