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- /*
- * modeset - DRM Double-Buffered VSync'ed Modesetting Example
- *
- * Written 2012 by David Rheinsberg <david.rheinsberg@gmail.com>
- * Dedicated to the Public Domain.
- */
- /*
- * DRM Double-Buffered VSync'ed Modesetting Howto
- * This example extends modeset-double-buffered.c and introduces page-flips
- * synced with vertical-blanks (vsync'ed). A vertical-blank is the time-period
- * when a display-controller pauses from scanning out the framebuffer. After the
- * vertical-blank is over, the framebuffer is again scanned out line by line and
- * followed again by a vertical-blank.
- *
- * Vertical-blanks are important when changing a framebuffer. We already
- * introduced double-buffering, so this example shows how we can flip the
- * buffers during a vertical blank and _not_ during the scanout period.
- *
- * This example assumes that you are familiar with modeset-double-buffered. Only
- * the differences between both files are highlighted here.
- */
- #define _GNU_SOURCE
- #include <errno.h>
- #include <fcntl.h>
- #include <stdbool.h>
- #include <stdint.h>
- #include <stdio.h>
- #include <stdlib.h>
- #include <string.h>
- #include <sys/mman.h>
- #include <time.h>
- #include <unistd.h>
- #include <xf86drm.h>
- #include <xf86drmMode.h>
- struct modeset_buf;
- struct modeset_dev;
- static int modeset_find_crtc(int fd, drmModeRes *res, drmModeConnector *conn,
- struct modeset_dev *dev);
- static int modeset_create_fb(int fd, struct modeset_buf *buf);
- static void modeset_destroy_fb(int fd, struct modeset_buf *buf);
- static int modeset_setup_dev(int fd, drmModeRes *res, drmModeConnector *conn,
- struct modeset_dev *dev);
- static int modeset_open(int *out, const char *node);
- static int modeset_prepare(int fd);
- static void modeset_draw(int fd);
- static void modeset_draw_dev(int fd, struct modeset_dev *dev);
- static void modeset_cleanup(int fd);
- /*
- * modeset_open() stays the same.
- */
- static int modeset_open(int *out, const char *node)
- {
- int fd, ret;
- uint64_t has_dumb;
- fd = open(node, O_RDWR | O_CLOEXEC);
- if (fd < 0) {
- ret = -errno;
- fprintf(stderr, "cannot open '%s': %m\n", node);
- return ret;
- }
- if (drmGetCap(fd, DRM_CAP_DUMB_BUFFER, &has_dumb) < 0 ||
- !has_dumb) {
- fprintf(stderr, "drm device '%s' does not support dumb buffers\n",
- node);
- close(fd);
- return -EOPNOTSUPP;
- }
- *out = fd;
- return 0;
- }
- /*
- * modeset_buf and modeset_dev stay mostly the same. But 6 new fields are added
- * to modeset_dev: r, g, b, r_up, g_up, b_up. They are used to compute the
- * current color that is drawn on this output device. You can ignore them as
- * they aren't important for this example.
- * The modeset-double-buffered.c example used exactly the same fields but as
- * local variables in modeset_draw().
- *
- * The \pflip_pending variable is true when a page-flip is currently pending,
- * that is, the kernel will flip buffers on the next vertical blank. The
- * \cleanup variable is true if the device is currently cleaned up and no more
- * pageflips should be scheduled. They are used to synchronize the cleanup
- * routines.
- */
- struct modeset_buf {
- uint32_t width;
- uint32_t height;
- uint32_t stride;
- uint32_t size;
- uint32_t handle;
- uint8_t *map;
- uint32_t fb;
- };
- struct modeset_dev {
- struct modeset_dev *next;
- unsigned int front_buf;
- struct modeset_buf bufs[2];
- drmModeModeInfo mode;
- uint32_t conn;
- uint32_t crtc;
- drmModeCrtc *saved_crtc;
- bool pflip_pending;
- bool cleanup;
- uint8_t r, g, b;
- bool r_up, g_up, b_up;
- };
- static struct modeset_dev *modeset_list = NULL;
- /*
- * modeset_prepare() stays the same.
- */
- static int modeset_prepare(int fd)
- {
- drmModeRes *res;
- drmModeConnector *conn;
- unsigned int i;
- struct modeset_dev *dev;
- int ret;
- /* retrieve resources */
- res = drmModeGetResources(fd);
- if (!res) {
- fprintf(stderr, "cannot retrieve DRM resources (%d): %m\n",
- errno);
- return -errno;
- }
- /* iterate all connectors */
- for (i = 0; i < res->count_connectors; ++i) {
- /* get information for each connector */
- conn = drmModeGetConnector(fd, res->connectors[i]);
- if (!conn) {
- fprintf(stderr, "cannot retrieve DRM connector %u:%u (%d): %m\n",
- i, res->connectors[i], errno);
- continue;
- }
- /* create a device structure */
- dev = malloc(sizeof(*dev));
- memset(dev, 0, sizeof(*dev));
- dev->conn = conn->connector_id;
- /* call helper function to prepare this connector */
- ret = modeset_setup_dev(fd, res, conn, dev);
- if (ret) {
- if (ret != -ENOENT) {
- errno = -ret;
- fprintf(stderr, "cannot setup device for connector %u:%u (%d): %m\n",
- i, res->connectors[i], errno);
- }
- free(dev);
- drmModeFreeConnector(conn);
- continue;
- }
- /* free connector data and link device into global list */
- drmModeFreeConnector(conn);
- dev->next = modeset_list;
- modeset_list = dev;
- }
- /* free resources again */
- drmModeFreeResources(res);
- return 0;
- }
- /*
- * modeset_setup_dev() stays the same.
- */
- static int modeset_setup_dev(int fd, drmModeRes *res, drmModeConnector *conn,
- struct modeset_dev *dev)
- {
- int ret;
- /* check if a monitor is connected */
- if (conn->connection != DRM_MODE_CONNECTED) {
- fprintf(stderr, "ignoring unused connector %u\n",
- conn->connector_id);
- return -ENOENT;
- }
- /* check if there is at least one valid mode */
- if (conn->count_modes == 0) {
- fprintf(stderr, "no valid mode for connector %u\n",
- conn->connector_id);
- return -EFAULT;
- }
- /* copy the mode information into our device structure and into both
- * buffers */
- memcpy(&dev->mode, &conn->modes[0], sizeof(dev->mode));
- dev->bufs[0].width = conn->modes[0].hdisplay;
- dev->bufs[0].height = conn->modes[0].vdisplay;
- dev->bufs[1].width = conn->modes[0].hdisplay;
- dev->bufs[1].height = conn->modes[0].vdisplay;
- fprintf(stderr, "mode for connector %u is %ux%u\n",
- conn->connector_id, dev->bufs[0].width, dev->bufs[0].height);
- /* find a crtc for this connector */
- ret = modeset_find_crtc(fd, res, conn, dev);
- if (ret) {
- fprintf(stderr, "no valid crtc for connector %u\n",
- conn->connector_id);
- return ret;
- }
- /* create framebuffer #1 for this CRTC */
- ret = modeset_create_fb(fd, &dev->bufs[0]);
- if (ret) {
- fprintf(stderr, "cannot create framebuffer for connector %u\n",
- conn->connector_id);
- return ret;
- }
- /* create framebuffer #2 for this CRTC */
- ret = modeset_create_fb(fd, &dev->bufs[1]);
- if (ret) {
- fprintf(stderr, "cannot create framebuffer for connector %u\n",
- conn->connector_id);
- modeset_destroy_fb(fd, &dev->bufs[0]);
- return ret;
- }
- return 0;
- }
- /*
- * modeset_find_crtc() stays the same.
- */
- static int modeset_find_crtc(int fd, drmModeRes *res, drmModeConnector *conn,
- struct modeset_dev *dev)
- {
- drmModeEncoder *enc;
- unsigned int i, j;
- int32_t crtc;
- struct modeset_dev *iter;
- /* first try the currently conected encoder+crtc */
- if (conn->encoder_id)
- enc = drmModeGetEncoder(fd, conn->encoder_id);
- else
- enc = NULL;
- if (enc) {
- if (enc->crtc_id) {
- crtc = enc->crtc_id;
- for (iter = modeset_list; iter; iter = iter->next) {
- if (iter->crtc == crtc) {
- crtc = -1;
- break;
- }
- }
- if (crtc >= 0) {
- drmModeFreeEncoder(enc);
- dev->crtc = crtc;
- return 0;
- }
- }
- drmModeFreeEncoder(enc);
- }
- /* If the connector is not currently bound to an encoder or if the
- * encoder+crtc is already used by another connector (actually unlikely
- * but lets be safe), iterate all other available encoders to find a
- * matching CRTC. */
- for (i = 0; i < conn->count_encoders; ++i) {
- enc = drmModeGetEncoder(fd, conn->encoders[i]);
- if (!enc) {
- fprintf(stderr, "cannot retrieve encoder %u:%u (%d): %m\n",
- i, conn->encoders[i], errno);
- continue;
- }
- /* iterate all global CRTCs */
- for (j = 0; j < res->count_crtcs; ++j) {
- /* check whether this CRTC works with the encoder */
- if (!(enc->possible_crtcs & (1 << j)))
- continue;
- /* check that no other device already uses this CRTC */
- crtc = res->crtcs[j];
- for (iter = modeset_list; iter; iter = iter->next) {
- if (iter->crtc == crtc) {
- crtc = -1;
- break;
- }
- }
- /* we have found a CRTC, so save it and return */
- if (crtc >= 0) {
- drmModeFreeEncoder(enc);
- dev->crtc = crtc;
- return 0;
- }
- }
- drmModeFreeEncoder(enc);
- }
- fprintf(stderr, "cannot find suitable CRTC for connector %u\n",
- conn->connector_id);
- return -ENOENT;
- }
- /*
- * modeset_create_fb() stays the same.
- */
- static int modeset_create_fb(int fd, struct modeset_buf *buf)
- {
- struct drm_mode_create_dumb creq;
- struct drm_mode_destroy_dumb dreq;
- struct drm_mode_map_dumb mreq;
- int ret;
- /* create dumb buffer */
- memset(&creq, 0, sizeof(creq));
- creq.width = buf->width;
- creq.height = buf->height;
- creq.bpp = 32;
- ret = drmIoctl(fd, DRM_IOCTL_MODE_CREATE_DUMB, &creq);
- if (ret < 0) {
- fprintf(stderr, "cannot create dumb buffer (%d): %m\n",
- errno);
- return -errno;
- }
- buf->stride = creq.pitch;
- buf->size = creq.size;
- buf->handle = creq.handle;
- /* create framebuffer object for the dumb-buffer */
- ret = drmModeAddFB(fd, buf->width, buf->height, 32, 32, buf->stride,
- buf->handle, &buf->fb);
- if (ret) {
- fprintf(stderr, "cannot create framebuffer (%d): %m\n",
- errno);
- ret = -errno;
- goto err_destroy;
- }
- /* prepare buffer for memory mapping */
- memset(&mreq, 0, sizeof(mreq));
- mreq.handle = buf->handle;
- ret = drmIoctl(fd, DRM_IOCTL_MODE_MAP_DUMB, &mreq);
- if (ret) {
- fprintf(stderr, "cannot map dumb buffer (%d): %m\n",
- errno);
- ret = -errno;
- goto err_fb;
- }
- /* perform actual memory mapping */
- buf->map = mmap(0, buf->size, PROT_READ | PROT_WRITE, MAP_SHARED,
- fd, mreq.offset);
- if (buf->map == MAP_FAILED) {
- fprintf(stderr, "cannot mmap dumb buffer (%d): %m\n",
- errno);
- ret = -errno;
- goto err_fb;
- }
- /* clear the framebuffer to 0 */
- memset(buf->map, 0, buf->size);
- return 0;
- err_fb:
- drmModeRmFB(fd, buf->fb);
- err_destroy:
- memset(&dreq, 0, sizeof(dreq));
- dreq.handle = buf->handle;
- drmIoctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &dreq);
- return ret;
- }
- /*
- * modeset_destroy_fb() stays the same.
- */
- static void modeset_destroy_fb(int fd, struct modeset_buf *buf)
- {
- struct drm_mode_destroy_dumb dreq;
- /* unmap buffer */
- munmap(buf->map, buf->size);
- /* delete framebuffer */
- drmModeRmFB(fd, buf->fb);
- /* delete dumb buffer */
- memset(&dreq, 0, sizeof(dreq));
- dreq.handle = buf->handle;
- drmIoctl(fd, DRM_IOCTL_MODE_DESTROY_DUMB, &dreq);
- }
- /*
- * main() also stays the same.
- */
- int main(int argc, char **argv)
- {
- int ret, fd;
- const char *card;
- struct modeset_dev *iter;
- struct modeset_buf *buf;
- /* check which DRM device to open */
- if (argc > 1)
- card = argv[1];
- else
- card = "/dev/dri/card0";
- fprintf(stderr, "using card '%s'\n", card);
- /* open the DRM device */
- ret = modeset_open(&fd, card);
- if (ret)
- goto out_return;
- /* prepare all connectors and CRTCs */
- ret = modeset_prepare(fd);
- if (ret)
- goto out_close;
- /* perform actual modesetting on each found connector+CRTC */
- for (iter = modeset_list; iter; iter = iter->next) {
- iter->saved_crtc = drmModeGetCrtc(fd, iter->crtc);
- buf = &iter->bufs[iter->front_buf];
- ret = drmModeSetCrtc(fd, iter->crtc, buf->fb, 0, 0,
- &iter->conn, 1, &iter->mode);
- if (ret)
- fprintf(stderr, "cannot set CRTC for connector %u (%d): %m\n",
- iter->conn, errno);
- }
- /* draw some colors for 5seconds */
- modeset_draw(fd);
- /* cleanup everything */
- modeset_cleanup(fd);
- ret = 0;
- out_close:
- close(fd);
- out_return:
- if (ret) {
- errno = -ret;
- fprintf(stderr, "modeset failed with error %d: %m\n", errno);
- } else {
- fprintf(stderr, "exiting\n");
- }
- return ret;
- }
- /*
- * modeset_page_flip_event() is a callback-helper for modeset_draw() below.
- * Please see modeset_draw() for more information.
- *
- * Note that this does nothing if the device is currently cleaned up. This
- * allows to wait for outstanding page-flips during cleanup.
- */
- static void modeset_page_flip_event(int fd, unsigned int frame,
- unsigned int sec, unsigned int usec,
- void *data)
- {
- struct modeset_dev *dev = data;
- dev->pflip_pending = false;
- if (!dev->cleanup)
- modeset_draw_dev(fd, dev);
- }
- /*
- * modeset_draw() changes heavily from all previous examples. The rendering has
- * moved into another helper modeset_draw_dev() below, but modeset_draw() is now
- * responsible of controlling when we have to redraw the outputs.
- *
- * So what we do: first redraw all outputs. We initialize the r/g/b/_up
- * variables of each output first, although, you can safely ignore these.
- * They're solely used to compute the next color. Then we call
- * modeset_draw_dev() for each output. This function _always_ redraws the output
- * and schedules a buffer-swap/flip for the next vertical-blank.
- * We now have to wait for each vertical-blank to happen so we can draw the next
- * frame. If a vblank happens, we simply call modeset_draw_dev() again and wait
- * for the next vblank.
- *
- * Note: Different monitors can have different refresh-rates. That means, a
- * vblank event is always assigned to a CRTC. Hence, we get different vblank
- * events for each CRTC/modeset_dev that we use. This also means, that our
- * framerate-controlled color-morphing is different on each monitor. If you want
- * exactly the same frame on all monitors, we would have to share the
- * color-values between all devices. However, for simplicity reasons, we don't
- * do this here.
- *
- * So the last piece missing is how we get vblank events. libdrm provides
- * drmWaitVBlank(), however, we aren't interested in _all_ vblanks, but only in
- * the vblanks for our page-flips. We could use drmWaitVBlank() but there is a
- * more convenient way: drmModePageFlip()
- * drmModePageFlip() schedules a buffer-flip for the next vblank and then
- * notifies us about it. It takes a CRTC-id, fb-id and an arbitrary
- * data-pointer and then schedules the page-flip. This is fully asynchronous and
- * returns immediately.
- * When the page-flip happens, the DRM-fd will become readable and we can call
- * drmHandleEvent(). This will read all vblank/page-flip events and call our
- * modeset_page_flip_event() callback with the data-pointer that we passed to
- * drmModePageFlip(). We simply call modeset_draw_dev() then so the next frame
- * is rendered..
- *
- *
- * So modeset_draw() is reponsible of waiting for the page-flip/vblank events
- * for _all_ currently used output devices and schedule a redraw for them. We
- * could easily do this in a while (1) { drmHandleEvent() } loop, however, this
- * example shows how you can use the DRM-fd to integrate this into your own
- * main-loop. If you aren't familiar with select(), poll() or epoll, please read
- * it up somewhere else. There is plenty of documentation elsewhere on the
- * internet.
- *
- * So what we do is adding the DRM-fd and the keyboard-input-fd (more precisely:
- * the stdin FD) to a select-set and then we wait on this set. If the DRM-fd is
- * readable, we call drmHandleEvents() to handle the page-flip events. If the
- * input-fd is readable, we exit. So on any keyboard input we exit this loop
- * (you need to press RETURN after each keyboard input to make this work).
- */
- static void modeset_draw(int fd)
- {
- int ret;
- fd_set fds;
- time_t start, cur;
- struct timeval v;
- drmEventContext ev;
- struct modeset_dev *iter;
- /* init variables */
- srand(time(&start));
- FD_ZERO(&fds);
- memset(&v, 0, sizeof(v));
- memset(&ev, 0, sizeof(ev));
- /* Set this to only the latest version you support. Version 2
- * introduced the page_flip_handler, so we use that. */
- ev.version = 2;
- ev.page_flip_handler = modeset_page_flip_event;
- /* redraw all outputs */
- for (iter = modeset_list; iter; iter = iter->next) {
- iter->r = rand() % 0xff;
- iter->g = rand() % 0xff;
- iter->b = rand() % 0xff;
- iter->r_up = iter->g_up = iter->b_up = true;
- modeset_draw_dev(fd, iter);
- }
- /* wait 5s for VBLANK or input events */
- while (time(&cur) < start + 5) {
- FD_SET(0, &fds);
- FD_SET(fd, &fds);
- v.tv_sec = start + 5 - cur;
- ret = select(fd + 1, &fds, NULL, NULL, &v);
- if (ret < 0) {
- fprintf(stderr, "select() failed with %d: %m\n", errno);
- break;
- } else if (FD_ISSET(0, &fds)) {
- fprintf(stderr, "exit due to user-input\n");
- break;
- } else if (FD_ISSET(fd, &fds)) {
- drmHandleEvent(fd, &ev);
- }
- }
- }
- /*
- * A short helper function to compute a changing color value. No need to
- * understand it.
- */
- static uint8_t next_color(bool *up, uint8_t cur, unsigned int mod)
- {
- uint8_t next;
- next = cur + (*up ? 1 : -1) * (rand() % mod);
- if ((*up && next < cur) || (!*up && next > cur)) {
- *up = !*up;
- next = cur;
- }
- return next;
- }
- /*
- * modeset_draw_dev() is a new function that redraws the screen of a single
- * output. It takes the DRM-fd and the output devices as arguments, redraws a
- * new frame and schedules the page-flip for the next vsync.
- *
- * This function does the same as modeset_draw() did in the previous examples
- * but only for a single output device now.
- * After we are done rendering a frame, we have to swap the buffers. Instead of
- * calling drmModeSetCrtc() as we did previously, we now want to schedule this
- * page-flip for the next vertical-blank (vblank). We use drmModePageFlip() for
- * this. It takes the CRTC-id and FB-id and will asynchronously swap the buffers
- * when the next vblank occurs. Note that this is done by the kernel, so neither
- * a thread is started nor any other magic is done in libdrm.
- * The DRM_MODE_PAGE_FLIP_EVENT flag tells drmModePageFlip() to send us a
- * page-flip event on the DRM-fd when the page-flip happened. The last argument
- * is a data-pointer that is returned with this event.
- * If we wouldn't pass this flag, we would not get notified when the page-flip
- * happened.
- *
- * Note: If you called drmModePageFlip() and directly call it again, it will
- * return EBUSY if the page-flip hasn't happened in between. So you almost
- * always want to pass DRM_MODE_PAGE_FLIP_EVENT to get notified when the
- * page-flip happens so you know when to render the next frame.
- * If you scheduled a page-flip but call drmModeSetCrtc() before the next
- * vblank, then the scheduled page-flip will become a no-op. However, you will
- * still get notified when it happens and you still cannot call
- * drmModePageFlip() again until it finished. So to sum it up: there is no way
- * to effectively cancel a page-flip.
- *
- * If you wonder why drmModePageFlip() takes fewer arguments than
- * drmModeSetCrtc(), then you should take into account, that drmModePageFlip()
- * reuses the arguments from drmModeSetCrtc(). So things like connector-ids,
- * x/y-offsets and so on have to be set via drmModeSetCrtc() first before you
- * can use drmModePageFlip()! We do this in main() as all the previous examples
- * did, too.
- */
- static void modeset_draw_dev(int fd, struct modeset_dev *dev)
- {
- struct modeset_buf *buf;
- unsigned int j, k, off;
- int ret;
- dev->r = next_color(&dev->r_up, dev->r, 20);
- dev->g = next_color(&dev->g_up, dev->g, 10);
- dev->b = next_color(&dev->b_up, dev->b, 5);
- buf = &dev->bufs[dev->front_buf ^ 1];
- for (j = 0; j < buf->height; ++j) {
- for (k = 0; k < buf->width; ++k) {
- off = buf->stride * j + k * 4;
- *(uint32_t*)&buf->map[off] =
- (dev->r << 16) | (dev->g << 8) | dev->b;
- }
- }
- ret = drmModePageFlip(fd, dev->crtc, buf->fb,
- DRM_MODE_PAGE_FLIP_EVENT, dev);
- if (ret) {
- fprintf(stderr, "cannot flip CRTC for connector %u (%d): %m\n",
- dev->conn, errno);
- } else {
- dev->front_buf ^= 1;
- dev->pflip_pending = true;
- }
- }
- /*
- * modeset_cleanup() stays mostly the same. However, before resetting a CRTC to
- * its previous state, we wait for any outstanding page-flip to complete. This
- * isn't strictly neccessary, however, some DRM drivers are known to be buggy if
- * we call drmModeSetCrtc() if there is a pending page-flip.
- * Furthermore, we don't want any pending page-flips when our application exist.
- * Because another application might pick up the DRM device and try to schedule
- * their own page-flips which might then fail as long as our page-flip is
- * pending.
- * So lets be safe here and simply wait for any page-flips to complete. This is
- * a blocking operation, but it's mostly just <16ms so we can ignore that.
- */
- static void modeset_cleanup(int fd)
- {
- struct modeset_dev *iter;
- drmEventContext ev;
- int ret;
- /* init variables */
- memset(&ev, 0, sizeof(ev));
- ev.version = DRM_EVENT_CONTEXT_VERSION;
- ev.page_flip_handler = modeset_page_flip_event;
- while (modeset_list) {
- /* remove from global list */
- iter = modeset_list;
- modeset_list = iter->next;
- /* if a pageflip is pending, wait for it to complete */
- iter->cleanup = true;
- fprintf(stderr, "wait for pending page-flip to complete...\n");
- while (iter->pflip_pending) {
- ret = drmHandleEvent(fd, &ev);
- if (ret)
- break;
- }
- /* restore saved CRTC configuration */
- if (!iter->pflip_pending)
- drmModeSetCrtc(fd,
- iter->saved_crtc->crtc_id,
- iter->saved_crtc->buffer_id,
- iter->saved_crtc->x,
- iter->saved_crtc->y,
- &iter->conn,
- 1,
- &iter->saved_crtc->mode);
- drmModeFreeCrtc(iter->saved_crtc);
- /* destroy framebuffers */
- modeset_destroy_fb(fd, &iter->bufs[1]);
- modeset_destroy_fb(fd, &iter->bufs[0]);
- /* free allocated memory */
- free(iter);
- }
- }
- /*
- * This example shows how to make the kernel handle page-flips and how to wait
- * for them in user-space. The select() example here should show you how you can
- * integrate these loops into your own applications without the need for a
- * separate modesetting thread.
- *
- * However, please note that vsync'ed double-buffering doesn't solve all
- * problems. Imagine that you cannot render a frame fast enough to satisfy all
- * vertical-blanks. In this situation, you don't want to wait after scheduling a
- * page-flip until the vblank happens to draw the next frame. A solution for
- * this is triple-buffering. It should be farily easy to extend this example to
- * use triple-buffering, but feel free to contact me if you have any questions
- * about it.
- * Also note that the DRM kernel API is quite limited if you want to reschedule
- * page-flips that haven't happened, yet. You cannot call drmModePageFlip()
- * twice in a single scanout-period. The behavior of drmModeSetCrtc() while a
- * page-flip is pending might also be unexpected.
- * Unfortunately, there is no ultimate solution to all modesetting problems.
- * This example shows the tools to do vsync'ed page-flips, however, it depends
- * on your use-case how you have to implement it.
- *
- * If you want more code, I can recommend reading the source-code of:
- * - plymouth (which uses dumb-buffers like this example; very easy to understand)
- * - kmscon (which uses libuterm to do this)
- * - wayland (very sophisticated DRM renderer; hard to understand fully as it
- * uses more complicated techniques like DRM planes)
- * - xserver (very hard to understand as it is split across many files/projects)
- *
- * Any feedback is welcome. Feel free to use this code freely for your own
- * documentation or projects.
- *
- * - Hosted on http://github.com/dvdhrm/docs
- * - Written by David Rheinsberg <david.rheinsberg@gmail.com>
- */
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