summaryrefslogtreecommitdiff
path: root/src/modules/flui2d/flui2d.c
blob: df980baf93b7c033a921c5a90c3d07f4318311bb (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
#include <errno.h>
#include <stdint.h>
#include <inttypes.h>
#include <math.h>
#include <stdlib.h>

#include "til.h"
#include "til_fb.h"
#include "til_module_context.h"
#include "til_settings.h"


/* This code is almost entirely taken from the paper:
 * Real-Time Fluid Dynamics for Games
 * Jos Stam - Alias | Wavefront
 *
 * I take zero credit for it, I only wrote the rototiller integration.
 *   - Vito Caputo <vcaputo@pengaru.com> 10/13/2019
 */

#define ROOT		128	// Change this to vary the density field resolution
#define SIZE		((ROOT + 2) * (ROOT + 2))
#define IX(i, j)	((i) + (ROOT + 2) * (j))
#define SWAP(x0, x)	{float *tmp = x0; x0 = x; x = tmp;}

typedef struct flui2d_t {
	float	u[SIZE], v[SIZE], u_prev[SIZE], v_prev[SIZE];
	float	dens_r[SIZE], dens_prev_r[SIZE];
	float	dens_g[SIZE], dens_prev_g[SIZE];
	float	dens_b[SIZE], dens_prev_b[SIZE];
	float	visc, diff, decay;
} flui2d_t;

static void set_bnd(int N, int b, float *x)
{
	for (int i = 1; i <= N; i++) {
		x[IX(0, i)] = b == 1 ? -x[IX(1, i)] : x[IX(1, i)];
		x[IX(N + 1, i)] = b == 1 ? -x[IX(N, i)] : x[IX(N, i)];
		x[IX(i, 0)] = b == 2 ? -x[IX(i, 1)] : x[IX(i, 1)];
		x[IX(i, N + 1)] = b == 2 ? -x[IX(i, N)] : x[IX(i, N)];
	}

	x[IX(0 , 0)] = 0.5 * (x[IX(1, 0)] + x[IX(0, 1)]);
	x[IX(0 , N + 1)] = 0.5 * (x[IX(1, N + 1)] + x[IX(0, N)]);
	x[IX(N + 1, 0)] = 0.5 * (x[IX(N, 0)] + x[IX(N + 1, 1)]);
	x[IX(N + 1, N + 1)] = 0.5 * (x[IX(N, N + 1)] + x[IX(N + 1, N)]);
}

static void add_source(int N, float *x, float *s, float dt)
{
	int	size = (N + 2) * (N + 2);

	for (int i = 0; i < size; i++)
		x[i] += dt * s[i];
}

static void diffuse(int N, int b, float *x, float *x0, float diff, float decay, float dt)
{
	float a = dt * diff * (float)N * (float)N;
	int i, j, k;
	float z = 1.f / (1.f + 4.f * a);

	for (k = 0; k < 20; k++) {
		for (i = 1; i <= N; i++) {
			for (j = 1; j <= N; j++) {
				x[IX(i, j)] = (x0[IX(i, j)] + a * (x[IX(i - 1, j)] + x[IX(i + 1, j)] + x[IX(i, j - 1)] + x[IX(i, j + 1)])) * z * (1.f - decay);
			}
		}
		set_bnd(N, b, x);
	}
}

static void advect(int N, int b, float *d, float *d0, float *u, float *v, float dt)
{
	float x, y, s0, t0, s1, t1, dt0;
	int i, j, i0, j0, i1, j1;

	dt0 = dt * (float)N;
	for (i = 1 ; i <= N ; i++) {
		for (j = 1 ; j <= N; j++) {
			x = (float)i - dt0 * u[IX(i, j)];
			y = (float)j - dt0 * v[IX(i, j)];

			if (x < .5f)
				x = .5f;
			if (x > (float)N + .5f)
				x = (float)N + .5f;

			i0 = (int)x;
			i1 = i0 + 1;

			if (y < .5f)
				y = .5f;
			if (y > (float)N + .5f)
				y = (float)N + .5f;

			j0 = (int)y;
			j1 = j0 + 1;

			s1 = x - (float)i0;
			s0 = 1.f - s1;
			t1 = y - (float)j0;
			t0 = 1.f - t1;

			d[IX(i, j)] = s0 * (t0 * d0[IX(i0, j0)] + t1 * d0[IX(i0, j1)]) + s1 * (t0 * d0[IX(i1, j0)] + t1 * d0[IX(i1, j1)]);
		}
	}
	set_bnd(N, b, d);
}

static void project(int N, float *u, float *v, float *p, float *div)
{
	float h = 1.f / (float)N;
	int i, j, k;

	for (i = 1; i <= N ; i++) {
		for (j = 1; j <= N; j++) {
			div[IX(i, j)] = -0.5 * h *(u[IX(i + 1, j)] - u[IX(i - 1, j)] + v[IX(i, j + 1)] - v[IX(i, j - 1)]);
			p[IX(i, j)] = 0;
		}
	}

	set_bnd(N, 0, div);
	set_bnd(N, 0, p);

	for (k = 0; k < 20; k++) {
		for (i = 1; i <= N; i++) {
			for (j = 1; j <= N; j++) {
				p[IX(i, j)] = (div[IX(i, j)] + p[IX(i - 1, j)] + p[IX(i + 1, j)] + p[IX(i, j - 1)] + p[IX(i, j + 1)]) * .25f;
			}
		}
		set_bnd(N, 0, p);
	}

	for (i = 1; i <= N; i++) {
		for (j = 1; j <= N; j++) {
			u[IX(i, j)] -= 0.5 * (p[IX(i + 1, j)] - p[IX(i - 1, j)]) / h;
			v[IX(i, j)] -= 0.5 * (p[IX(i, j + 1)] - p[IX(i, j - 1)]) / h;
		}
	}

	set_bnd(N, 1, u);
	set_bnd(N, 2, v);
}

static void dens_step(int N, float *x, float *x0, float *u, float *v, float diff, float decay, float dt)
{

	/*
	 * The paper includes this, but it blows up the simulation.
	 * add_source(N, x, x0, dt);
	 * SWAP(x0, x);
	 */
	diffuse(N, 0, x, x0, diff, decay, dt);
	SWAP(x0, x);
	advect(N, 0, x, x0, u, v, dt);
}

static void vel_step(int N, float *u, float *v, float *u0, float *v0, float visc, float dt)
{
	add_source(N, u, u0, dt);
	add_source(N, v, v0, dt);
	SWAP(u0, u);
	diffuse(N, 1, u, u0, visc, 0.f, dt);
	SWAP(v0, v);
	diffuse(N, 2, v, v0, visc, 0.f, dt);
	project(N, u, v, u0, v0);
	SWAP(u0, u);
	SWAP(v0, v);
	advect(N, 1, u, u0, u0, v0, dt);
	advect(N, 2, v, v0, u0, v0, dt);
	project(N, u, v, u0, v0);
}

typedef enum flui2d_emitters_t {
	FLUI2D_EMITTERS_FIGURE8 = 0,	/* this is the original/classic figure eight */
	FLUI2D_EMITTERS_CLOCKGRID,
} flui2d_emitters_t;

typedef struct flui2d_setup_t {
	til_setup_t		til_setup;
	float			viscosity;
	float			diffusion;
	float			decay;
	flui2d_emitters_t	emitters;
	float			clockstep;
} flui2d_setup_t;

typedef struct flui2d_context_t {
	til_module_context_t	til_module_context;
	flui2d_t		fluid;
	flui2d_emitters_t	emitters;
	float			clockstep;
	float			xf, yf;
} flui2d_context_t;

#define FLUI2D_DEFAULT_EMITTERS		FLUI2D_EMITTERS_FIGURE8
#define FLUI2D_DEFAULT_CLOCKSTEP	.5

	/* These knobs affect how the simulated fluid behaves */
#define FLUI2D_DEFAULT_VISCOSITY	.000000001
#define FLUI2D_DEFAULT_DIFFUSION	.00001
#define FLUI2D_DEFAULT_DECAY		.0001


static flui2d_setup_t flui2d_default_setup = {
	.viscosity = FLUI2D_DEFAULT_VISCOSITY,
	.diffusion = FLUI2D_DEFAULT_DIFFUSION,
	.decay = FLUI2D_DEFAULT_DECAY,
	.emitters = FLUI2D_DEFAULT_EMITTERS,
};


/* gamma correction derived from libs/ray/ray_gamma.[ch] */
static uint8_t	gamma_table[1024];


static inline uint32_t gamma_color_to_uint32_rgb(float r, float g, float b) {
	uint32_t	pixel;

	if (r > 1.0f)
		r = 1.0f;

	if (g > 1.0f)
		g = 1.0f;

	if (b > 1.0f)
		b = 1.0f;

	pixel = (uint32_t)gamma_table[(unsigned)floorf(1023.0f * r)];
	pixel <<= 8;
	pixel |= (uint32_t)gamma_table[(unsigned)floorf(1023.0f * g)];
	pixel <<= 8;
	pixel |= (uint32_t)gamma_table[(unsigned)floorf(1023.0f * b)];

	return pixel;
}


static void gamma_init(float gamma)
{
	/* This is from graphics gems 2 "REAL PIXELS" */
	for (unsigned i = 0; i < 1024; i++)
		gamma_table[i] = 256.0f * powf((((float)i + .5f) / 1024.0f), 1.0f/gamma);
}


static til_module_context_t * flui2d_create_context(unsigned seed, unsigned ticks, unsigned n_cpus, til_setup_t *setup)
{
	static int		initialized;
	flui2d_context_t	*ctxt;

	if (!setup)
		setup = &flui2d_default_setup.til_setup;

	ctxt = til_module_context_new(sizeof(flui2d_context_t), seed, n_cpus);
	if (!ctxt)
		return NULL;

	if (!initialized) {
		initialized = 1;
		gamma_init(1.4f);
	}

	ctxt->fluid.visc = ((flui2d_setup_t *)setup)->viscosity;
	ctxt->fluid.diff = ((flui2d_setup_t *)setup)->diffusion;
	ctxt->fluid.decay = ((flui2d_setup_t *)setup)->decay;
	ctxt->emitters = ((flui2d_setup_t *)setup)->emitters;
	ctxt->clockstep = ((flui2d_setup_t *)setup)->clockstep;

	return &ctxt->til_module_context;
}


/* Prepare a frame for concurrent drawing of fragment using multiple fragments */
static void flui2d_prepare_frame(til_module_context_t *context, unsigned ticks, til_fb_fragment_t *fragment, til_fragmenter_t *res_fragmenter)
{
	flui2d_context_t	*ctxt = (flui2d_context_t *)context;
	float			r = (ticks % (unsigned)(2 * M_PI * 1000)) * .001f;

	*res_fragmenter = til_fragmenter_tile64;

	switch (ctxt->emitters) {
	case FLUI2D_EMITTERS_FIGURE8: {
		int	x = (cos(r) * .4f + .5f) * (float)ROOT;	/* figure eight pattern for the added densities */
		int	y = (sin(r * 2.f) * .4f + .5f) * (float)ROOT;

		ctxt->fluid.dens_prev_r[IX(x, y)] = .5f + cos(r) * .5f;
		ctxt->fluid.dens_prev_g[IX(x, y)] = .5f + sin(r) * .5f;
		ctxt->fluid.dens_prev_b[IX(x, y)] = .5f + cos(r * 2.f) * .5f;

		/* This orientation for the added velocities at the added densities isn't trying to
		 * emulate any sort of physical relationship to the movement - it's just creating a variety
		 * of turbulence.  It'd be trivial to make it look like a rocket's jetstream or something.
		 */
		ctxt->fluid.u_prev[IX(x, y)] = cos(r * 3.f) * 10.f;
		ctxt->fluid.v_prev[IX(x, y)] = sin(r * 3.f) * 10.f;
		break;
	}

	case FLUI2D_EMITTERS_CLOCKGRID: {
#define FLUI2D_CLOCKGRID_SIZE	(ROOT>>4)
#define FLUI2D_CLOCKGRID_STEP	(ROOT/FLUI2D_CLOCKGRID_SIZE)
		for (int y = FLUI2D_CLOCKGRID_STEP; y < ROOT; y += FLUI2D_CLOCKGRID_STEP) {
			for (int x = FLUI2D_CLOCKGRID_STEP; x < ROOT; x += FLUI2D_CLOCKGRID_STEP, r += ctxt->clockstep * M_PI * 2) {

				ctxt->fluid.dens_prev_r[IX(x, y)] = .5f + cos(r) * .5f;
				ctxt->fluid.dens_prev_g[IX(x, y)] = .5f + sin(r) * .5f;
				ctxt->fluid.dens_prev_b[IX(x, y)] = .5f + cos(r * 2.f) * .5f;

				ctxt->fluid.u_prev[IX(x, y)] = cos(r * 3.f);
				ctxt->fluid.v_prev[IX(x, y)] = sin(r * 3.f);
			}
		}
		break;
	}
	}

	/* These are the core of the simulation, and can't currently be threaded using the paper's implementation, so they
	 * must occur serialized here in prepare_frame.  It would be interesting to try refactor the API and tweak the
	 * implementation for threading, as it would really open up larger field sizes as well as map more naturally to
	 * a GLSL implementation for a fragment shader.
	 */
	vel_step(ROOT, ctxt->fluid.u, ctxt->fluid.v, ctxt->fluid.u_prev, ctxt->fluid.v_prev, ctxt->fluid.visc, .1f);
	dens_step(ROOT, ctxt->fluid.dens_r, ctxt->fluid.dens_prev_r, ctxt->fluid.u, ctxt->fluid.v, ctxt->fluid.diff, ctxt->fluid.decay, .1f);
	dens_step(ROOT, ctxt->fluid.dens_g, ctxt->fluid.dens_prev_g, ctxt->fluid.u, ctxt->fluid.v, ctxt->fluid.diff, ctxt->fluid.decay, .1f);
	dens_step(ROOT, ctxt->fluid.dens_b, ctxt->fluid.dens_prev_b, ctxt->fluid.u, ctxt->fluid.v, ctxt->fluid.diff, ctxt->fluid.decay, .1f);

	ctxt->xf = 1.f / fragment->frame_width;
	ctxt->yf = 1.f / fragment->frame_height;
}


/* Draw a the flui2d densities */
static void flui2d_render_fragment(til_module_context_t *context, unsigned ticks, unsigned cpu, til_fb_fragment_t *fragment)
{
	flui2d_context_t	*ctxt = (flui2d_context_t *)context;

	for (int y = fragment->y; y < fragment->y + fragment->height; y++) {
		int	y0, y1;
		float	Y;

		Y = (float)y * ctxt->yf * (float)ROOT;
		y0 = (int)Y;
		y1 = y0 + 1;

		for (int x = fragment->x; x < fragment->x + fragment->width; x++) {
			float		X, dens, dx0, dx1;
			int		x0, x1;
			float		r, g, b;

			X = (float)x * ctxt->xf * (float)ROOT;
			x0 = (int)X;
			x1 = x0 + 1;

			/* linear interpolation of density samples */
			dx0 = ctxt->fluid.dens_r[(int)IX(x0, y0)] * (1.f - (X - x0));
			dx0 += ctxt->fluid.dens_r[(int)IX(x1, y0)] * (X - x0);
			dx1 = ctxt->fluid.dens_r[(int)IX(x0, y1)] * (1.f - (X - x0));
			dx1 += ctxt->fluid.dens_r[(int)IX(x1, y1)] * (X - x0);
			r = dx0 * (1.f - (Y - y0)) + dx1 * (Y - y0);

			dx0 = ctxt->fluid.dens_g[(int)IX(x0, y0)] * (1.f - (X - x0));
			dx0 += ctxt->fluid.dens_g[(int)IX(x1, y0)] * (X - x0);
			dx1 = ctxt->fluid.dens_g[(int)IX(x0, y1)] * (1.f - (X - x0));
			dx1 += ctxt->fluid.dens_g[(int)IX(x1, y1)] * (X - x0);
			g = dx0 * (1.f - (Y - y0)) + dx1 * (Y - y0);

			dx0 = ctxt->fluid.dens_b[(int)IX(x0, y0)] * (1.f - (X - x0));
			dx0 += ctxt->fluid.dens_b[(int)IX(x1, y0)] * (X - x0);
			dx1 = ctxt->fluid.dens_b[(int)IX(x0, y1)] * (1.f - (X - x0));
			dx1 += ctxt->fluid.dens_b[(int)IX(x1, y1)] * (X - x0);
			b = dx0 * (1.f - (Y - y0)) + dx1 * (Y - y0);

			til_fb_fragment_put_pixel_unchecked(fragment, 0, x, y, gamma_color_to_uint32_rgb(r, g, b));
		}
	}
}


/* Settings hooks for configurable variables */
static int flui2d_setup(const til_settings_t *settings, til_setting_t **res_setting, const til_setting_desc_t **res_desc, til_setup_t **res_setup)
{
	const char	*viscosity;
	const char	*diffusion;
	const char	*values[] = {
				".000000000001",
				".0000000001",
				".000000001",
				".00000001",
				".0000001",
				".000001",
				".00001",
				".0001",
				NULL
			};
	const char	*decay;
	const char	*decay_values[] = {
				".000001",
				".00001",
				".0001",
				".001",
				".01",
				NULL
			};
	const char	*emitters;
	const char	*emitters_values[] = {
				"figure8",
				"clockgrid",
				NULL
			};
	const char	*clockstep;
	const char	*clockstep_values[] = {
				".05",
				".1",
				".25",
				".33",
				".50",
				".66",
				".75",
				".99",
				NULL
			};
	int		r;

	r = til_settings_get_and_describe_value(settings,
						&(til_setting_desc_t){
							.name = "Fluid viscosity",
							.key = "viscosity",
							.regex = "\\.[0-9]+",
							.preferred = TIL_SETTINGS_STR(FLUI2D_DEFAULT_VISCOSITY),
							.values = values,
							.annotations = NULL
						},
						&viscosity,
						res_setting,
						res_desc);
	if (r)
		return r;

	r = til_settings_get_and_describe_value(settings,
						&(til_setting_desc_t){
							.name = "Fluid diffusion",
							.key = "diffusion",
							.regex = "\\.[0-9]+",
							.preferred = TIL_SETTINGS_STR(FLUI2D_DEFAULT_DIFFUSION),
							.values = values,
							.annotations = NULL
						},
						&diffusion,
						res_setting,
						res_desc);
	if (r)
		return r;

	r = til_settings_get_and_describe_value(settings,
						&(til_setting_desc_t){
							.name = "Fluid decay",
							.key = "decay",
							.regex = "\\.[0-9]+",
							.preferred = TIL_SETTINGS_STR(FLUI2D_DEFAULT_DECAY),
							.values = decay_values,
							.annotations = NULL
						},
						&decay,
						res_setting,
						res_desc);
	if (r)
		return r;

	r = til_settings_get_and_describe_value(settings,
						&(til_setting_desc_t){
							.name = "Fluid emitters style",
							.key = "emitters",
							.regex = "^(figure8|clockgrid)",
							.preferred = emitters_values[FLUI2D_DEFAULT_EMITTERS],
							.values = emitters_values,
							.annotations = NULL
						},
						&emitters,
						res_setting,
						res_desc);
	if (r)
		return r;

	if (!strcasecmp(emitters, "clockgrid")) {
		r = til_settings_get_and_describe_value(settings,
							&(til_setting_desc_t){
								.name = "Fluid clockgrid emitters clock step",
								.key = "clockstep",
								.regex = "\\.[0-9]+",
								.preferred = TIL_SETTINGS_STR(FLUI2D_DEFAULT_CLOCKSTEP),
								.values = clockstep_values,
								.annotations = NULL
							},
							&clockstep,
							res_setting,
							res_desc);
		if (r)
			return r;
	}

	if (res_setup) {
		flui2d_setup_t	*setup;

		setup = til_setup_new(sizeof(*setup), (void(*)(til_setup_t *))free);
		if (!setup)
			return -ENOMEM;

		/* TODO: return -EINVAL on parse errors? */
		sscanf(viscosity, "%f", &setup->viscosity);
		sscanf(diffusion, "%f", &setup->diffusion);
		sscanf(decay, "%f", &setup->decay);

		/* prevent overflow in case an explicit out of range setting is supplied */
		if (setup->decay > 1.f || setup->decay < 0.f) {
			free(setup);
			return -EINVAL;
		}

		for (int i = 0; emitters_values[i]; i++) {
			if (!strcasecmp(emitters, emitters_values[i])) {
				setup->emitters = i;

				break;
			}
		}

		if (setup->emitters == FLUI2D_EMITTERS_CLOCKGRID)
			 sscanf(clockstep, "%f", &setup->clockstep);

		*res_setup = &setup->til_setup;
	}

	return 0;
}


til_module_t	flui2d_module = {
	.create_context = flui2d_create_context,
	.prepare_frame = flui2d_prepare_frame,
	.render_fragment = flui2d_render_fragment,
	.setup = flui2d_setup,
	.name = "flui2d",
	.description = "Fluid dynamics simulation in 2D (threaded (poorly))",
	.author = "Vito Caputo <vcaputo@pengaru.com>",
};
© All Rights Reserved