summaryrefslogtreecommitdiff
path: root/src/fb.c
blob: 255d90a0b5a375e8695e9e4a72294cf3c32e01a5 (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
#include <assert.h>
#include <pthread.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdint.h>

#include "fb.h"
#include "settings.h"
#include "util.h"

/* Copyright (C) 2016-2017 Vito Caputo <vcaputo@pengaru.com> */


/* I've used a separate thread for page-flipping duties because the libdrm api
 * (and related kernel ioctl) for page flips doesn't appear to support queueing
 * multiple flip requests.  In this use case we aren't interactive and wish to
 * just accumulate rendered pages until we run out of spare pages, allowing the
 * renderer to get as far ahead of vsync as possible, and certainly never
 * blocked waiting for vsync unless there's no spare page available for drawing
 * into.
 *
 * In lieu of a queueing mechanism on the drm fd, we must submit the next page
 * once the currently submitted page is flipped to - it's at that moment we
 * won't get EBUSY from the ioctl any longer.  Without a dedicated thread
 * submitting flip requests and synchronously consuming their flip events,
 * we're liable to introduce latency in the page flip submission if implemented
 * in a more opportunistic manner whenever the fb api is entered from the
 * render loop.
 *
 * If the kernel simply let us queue multiple flip requests we could maintain
 * our submission queue entirely in the drm fd, and get available pages from
 * the drm event handler once our pool of pages is depleted.  The kernel on
 * vsync could check the fd to see if another flip is queued and there would be
 * the least latency possible in submitting the flips - the least likely to
 * miss a vsync.  This would also elide the need for synchronization in
 * userspace between the renderer and the flipper thread, since there would no
 * longer be a flipper thread.
 *
 * Let me know if you're aware of a better way with existing mainline drm!
 *
 *
 * XXX: fb_new() used to create a thread which did the equivalent of fb_flip()
 * continuously in a loop.  This posed a problem for the sdl_fb backend, due to
 * the need for event pumping in the page flip hook.  SDL internally uses TLS
 * and requires that the same thread which initialized SDL call the event
 * functions.  To satisfy this requirement, the body of the flipper thread loop
 * has been moved to the fb_flip() function.  Rototiller's main thread is
 * expected to call this repeatedly, turning it effectively into the flipper
 * thread.  This required rototiller to move what was previously the main
 * thread's duties - page rendering dispatch, to a separate thread.
 */


/* Most of fb_page_t is kept private, the public part is
 * just an fb_fragment_t describing the whole page.
 */
typedef struct _fb_page_t _fb_page_t;
struct _fb_page_t {
	void		*ops_page;

	_fb_page_t	*next, *previous;
	fb_page_t	public_page;
};

typedef struct fb_t {
	const fb_ops_t	*ops;
	void		*ops_context;
	int		n_pages;

	pthread_mutex_t	rebuild_mutex;
	int		rebuild_pages;		/* counter of pages needing a rebuild */

	_fb_page_t	*active_page;		/* page currently displayed */

	pthread_mutex_t	ready_mutex;
	pthread_cond_t	ready_cond;
	_fb_page_t	*ready_pages_head;	/* next pages to flip to */
	_fb_page_t	*ready_pages_tail;

	pthread_mutex_t	inactive_mutex;
	pthread_cond_t	inactive_cond;
	_fb_page_t	*inactive_pages_head;	/* finished pages available for (re)use */
	_fb_page_t	*inactive_pages_tail;

	unsigned	put_pages_count;
} fb_t;

#ifndef container_of
#define container_of(_ptr, _type, _member) \
	(_type *)((void *)(_ptr) - offsetof(_type, _member))
#endif


/* Consumes ready pages queued via fb_page_put(), submits them to drm to flip
 * on vsync.  Produces inactive pages from those replaced, making them
 * available to fb_page_get(). */
int fb_flip(fb_t *fb)
{
	_fb_page_t	*next_active_page;
	int		r;

	/* wait for a flip req, submit the req page for flip on vsync, wait for it to flip before making the
	 * active page inactive/available, repeat.
	 */
	pthread_mutex_lock(&fb->ready_mutex);
	while (!fb->ready_pages_head)
		pthread_cond_wait(&fb->ready_cond, &fb->ready_mutex);

	next_active_page = fb->ready_pages_head;
	fb->ready_pages_head = next_active_page->next;
	if (!fb->ready_pages_head)
		fb->ready_pages_tail = NULL;
	pthread_mutex_unlock(&fb->ready_mutex);

	/* submit the next active page for page flip on vsync, and wait for it. */
	r = fb->ops->page_flip(fb, fb->ops_context, next_active_page->ops_page);
	if (r < 0)	/* TODO: vet this: what happens to this page? */
		return r;

	/* now that we're displaying a new page, make the previously active one inactive so rendering can reuse it */
	pthread_mutex_lock(&fb->inactive_mutex);
	fb->active_page->next = fb->inactive_pages_head;
	fb->inactive_pages_head = fb->active_page;
	fb->inactive_pages_head->previous = NULL;
	if (fb->inactive_pages_head->next)
		fb->inactive_pages_head->next->previous = fb->inactive_pages_head;
	else
		fb->inactive_pages_tail = fb->inactive_pages_head;

	/* before setting the renderer loose, check if there's more page rebuilding needed,
	 * and if there is do as much as possible here in the inactive set.  Note it's important
	 * that the renderer take pages from the tail, and we always replenish inactive at the
	 * head, as well as rebuild pages from the head.
	 */
	pthread_mutex_lock(&fb->rebuild_mutex);
	for (_fb_page_t *p = fb->inactive_pages_head; p && fb->rebuild_pages > 0; p = p->next) {
		fb->ops->page_free(fb, fb->ops_context, p->ops_page);
		p->ops_page = fb->ops->page_alloc(fb, fb->ops_context, &p->public_page);
		fb->rebuild_pages--;
	}
	pthread_mutex_unlock(&fb->rebuild_mutex);

	pthread_cond_signal(&fb->inactive_cond);
	pthread_mutex_unlock(&fb->inactive_mutex);

	fb->active_page = next_active_page;

	return 0;
}


/* acquire the fb, making page the visible page */
static int fb_acquire(fb_t *fb, _fb_page_t *page)
{
	int	ret;

	ret = fb->ops->acquire(fb, fb->ops_context, page->ops_page);
	if (ret < 0)
		return ret;

	fb->active_page = page;

	return 0;
}


/* release the fb, making the visible page inactive */
static void fb_release(fb_t *fb)
{
	fb->ops->release(fb, fb->ops_context);

	/* XXX: this is getting silly, either add a doubly linked list header or
	 * at least use some functions for this local to this file.
	 */
	fb->active_page->next = fb->inactive_pages_head;
	fb->inactive_pages_head = fb->active_page;
	fb->inactive_pages_head->previous = NULL;
	if (fb->inactive_pages_head->next)
		fb->inactive_pages_head->next->previous = fb->inactive_pages_head;
	else
		fb->inactive_pages_tail = fb->inactive_pages_head;

	fb->active_page = NULL;
}


/* creates a framebuffer page */
static void fb_page_new(fb_t *fb)
{
	_fb_page_t	*page;

	page = calloc(1, sizeof(_fb_page_t));
	assert(page);

	page->ops_page = fb->ops->page_alloc(fb, fb->ops_context, &page->public_page);

	pthread_mutex_lock(&fb->inactive_mutex);
	page->next = fb->inactive_pages_head;
	fb->inactive_pages_head = page;
	if (fb->inactive_pages_head->next)
		fb->inactive_pages_head->next->previous = fb->inactive_pages_head;
	else
		fb->inactive_pages_tail = fb->inactive_pages_head;
	pthread_mutex_unlock(&fb->inactive_mutex);

}


static void _fb_page_free(fb_t *fb, _fb_page_t *page)
{
	fb->ops->page_free(fb, fb->ops_context, page->ops_page);

	free(page);
}


/* get the next inactive page from the fb, waiting if necessary. */
static inline _fb_page_t * _fb_page_get(fb_t *fb)
{
	_fb_page_t	*page;

	/* As long as n_pages is >= 3 this won't block unless we're submitting
	 * pages faster than vhz.
	 */
	pthread_mutex_lock(&fb->inactive_mutex);
	while (!(page = fb->inactive_pages_tail))
		pthread_cond_wait(&fb->inactive_cond, &fb->inactive_mutex);
	fb->inactive_pages_tail = page->previous;
	if (fb->inactive_pages_tail)
		fb->inactive_pages_tail->next = NULL;
	else
		fb->inactive_pages_head = NULL;
	pthread_mutex_unlock(&fb->inactive_mutex);

	page->next = page->previous = NULL;
	page->public_page.fragment.zeroed = 0;

	return page;
}


/* public interface */
fb_page_t * fb_page_get(fb_t *fb)
{
	return &(_fb_page_get(fb)->public_page);
}


/* put a page into the fb, queueing for display */
static inline void _fb_page_put(fb_t *fb, _fb_page_t *page)
{
	pthread_mutex_lock(&fb->ready_mutex);
	if (fb->ready_pages_tail)
		fb->ready_pages_tail->next = page;
	else
		fb->ready_pages_head = page;

	fb->ready_pages_tail = page;
	pthread_cond_signal(&fb->ready_cond);
	pthread_mutex_unlock(&fb->ready_mutex);
}


/* public interface */

/* put a page into the fb, queueing for display */
void fb_page_put(fb_t *fb, fb_page_t *page)
{
	fb->put_pages_count++;

	_fb_page_put(fb, container_of(page, _fb_page_t, public_page));
}


/* get (and reset) the current count of put pages */
void fb_get_put_pages_count(fb_t *fb, unsigned *count)
{
	*count = fb->put_pages_count;
	fb->put_pages_count = 0;
}


/* free the fb and associated resources */
fb_t * fb_free(fb_t *fb)
{
	if (fb) {
		if (fb->active_page)
			fb_release(fb);

		/* TODO: free all the pages */

		if (fb->ops->shutdown && fb->ops_context)
			fb->ops->shutdown(fb, fb->ops_context);

		pthread_mutex_destroy(&fb->ready_mutex);
		pthread_cond_destroy(&fb->ready_cond);
		pthread_mutex_destroy(&fb->inactive_mutex);
		pthread_cond_destroy(&fb->inactive_cond);

		free(fb);
	}

	return NULL;
}


/* create a new fb instance */
int fb_new(const fb_ops_t *ops, settings_t *settings, int n_pages, fb_t **res_fb)
{
	_fb_page_t	*page;
	fb_t		*fb;
	int		r;

	assert(ops);
	assert(ops->page_alloc);
	assert(ops->page_free);
	assert(ops->page_flip);
	assert(n_pages > 1);
	assert(res_fb);

	/* XXX: page-flipping is the only supported rendering model, requiring 2+ pages. */
	if (n_pages < 2)
		return -EINVAL;

	fb = calloc(1, sizeof(fb_t));
	if (!fb)
		return -ENOMEM;

	fb->ops = ops;
	if (ops->init) {
		r = ops->init(settings, &fb->ops_context);
		if (r < 0)
			goto fail;
	}

	for (int i = 0; i < n_pages; i++)
		fb_page_new(fb);

	fb->n_pages = n_pages;

	pthread_mutex_init(&fb->ready_mutex, NULL);
	pthread_cond_init(&fb->ready_cond, NULL);
	pthread_mutex_init(&fb->inactive_mutex, NULL);
	pthread_cond_init(&fb->inactive_cond, NULL);
	pthread_mutex_init(&fb->rebuild_mutex, NULL);

	page = _fb_page_get(fb);
	if (!page) {
		r = -ENOMEM;
		goto fail;
	}

	r = fb_acquire(fb, page);
	if (r < 0)
		goto fail;

	*res_fb = fb;

	return r;

fail:
	fb_free(fb);

	return r;
}


/* This informs the fb to reconstruct its pages as they become invalid,
 * giving the backend an opportunity to reconfigure them before they get
 * rendered to again.  It's intended to be used in response to window
 * resizes.
 */
void fb_rebuild(fb_t *fb)
{
	assert(fb);

	/* TODO: this could easily be an atomic counter since we have no need for waiting */
	pthread_mutex_lock(&fb->rebuild_mutex);
	fb->rebuild_pages = fb->n_pages;
	pthread_mutex_unlock(&fb->rebuild_mutex);
}


/* helpers for fragmenting incrementally */
int fb_fragment_slice_single(const fb_fragment_t *fragment, unsigned n_fragments, unsigned number, fb_fragment_t *res_fragment)
{
	unsigned	slice = fragment->height / n_fragments;
	unsigned	yoff = slice * number;
	unsigned	pitch;

	if (yoff >= fragment->height)
		return 0;

	res_fragment->buf = ((void *)fragment->buf) + yoff * fragment->pitch;
	res_fragment->x = fragment->x;
	res_fragment->y = yoff;
	res_fragment->width = fragment->width;
	res_fragment->height = MIN(fragment->height - yoff, slice);
	res_fragment->frame_width = fragment->frame_width;
	res_fragment->frame_height = fragment->frame_height;
	res_fragment->stride = fragment->stride;
	res_fragment->pitch = fragment->pitch;
	res_fragment->number = number;
	res_fragment->zeroed = fragment->zeroed;

	return 1;
}


int fb_fragment_tile_single(const fb_fragment_t *fragment, unsigned tile_size, unsigned number, fb_fragment_t *res_fragment)
{
	unsigned	w = fragment->width / tile_size, h = fragment->height / tile_size;
	unsigned	x, y, xoff, yoff;

	if (w * tile_size < fragment->width)
		w++;

	if (h * tile_size < fragment->height)
		h++;

	y = number / w;
	if (y >= h)
		return 0;

	x = number - (y * w);

	xoff = x * tile_size;
	yoff = y * tile_size;

	res_fragment->buf = (void *)fragment->buf + (yoff * fragment->pitch) + (xoff * 4);
	res_fragment->x = fragment->x + xoff;
	res_fragment->y = fragment->y + yoff;
	res_fragment->width = MIN(fragment->width - xoff, tile_size);
	res_fragment->height = MIN(fragment->height - yoff, tile_size);
	res_fragment->frame_width = fragment->frame_width;
	res_fragment->frame_height = fragment->frame_height;
	res_fragment->stride = fragment->stride + ((fragment->width - res_fragment->width) * 4);
	res_fragment->pitch = fragment->pitch;
	res_fragment->number = number;

	return 1;
}
© 2021 All Rights Reserved