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[KMS/DRM] Small fix to KMSDRM_Waitpageflip(). More comments on how it works.
This commit is contained in:
Manuel Alfayate Corchete
parent
bdb3e6b84f
commit
03665004d0
@ -99,7 +99,7 @@ KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window) {
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/* Wait for confirmation that the next front buffer has been flipped, at which
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point the previous front buffer can be released */
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if (!KMSDRM_WaitPageFlip(_this, windata)) {
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if (!KMSDRM_WaitPageflip(_this, windata)) {
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SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "Wait for previous pageflip failed");
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return 0;
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}
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@ -182,16 +182,16 @@ KMSDRM_GLES_SwapWindow(_THIS, SDL_Window * window) {
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}
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/* Wait immediately for vsync (as if we only had two buffers).
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Even if we are already doing a WaitPageFlip at the begining of this
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Even if we are already doing a WaitPageflip at the begining of this
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function, this is NOT redundant because here we wait immediately
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after submitting the image to the screen, reducing lag, and if
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we have waited here, there won't be a pending pageflip so the
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WaitPageFlip at the beggining of this function will be a no-op.
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WaitPageflip at the beggining of this function will be a no-op.
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Just leave it here and don't worry.
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Run your SDL2 program with "SDL_KMSDRM_DOUBLE_BUFFER=1 <program_name>"
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to enable this. */
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if (windata->double_buffer) {
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if (!KMSDRM_WaitPageFlip(_this, windata)) {
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if (!KMSDRM_WaitPageflip(_this, windata)) {
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SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "Immediate wait for previous pageflip failed");
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return 0;
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}
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@ -341,11 +341,12 @@ KMSDRM_FlipHandler(int fd, unsigned int frame, unsigned int sec, unsigned int us
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}
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SDL_bool
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KMSDRM_WaitPageFlip(_THIS, SDL_WindowData *windata) {
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KMSDRM_WaitPageflip(_THIS, SDL_WindowData *windata) {
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SDL_VideoData *viddata = ((SDL_VideoData *)_this->driverdata);
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drmEventContext ev = {0};
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struct pollfd pfd = {0};
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int ret;
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ev.version = DRM_EVENT_CONTEXT_VERSION;
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ev.page_flip_handler = KMSDRM_FlipHandler;
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@ -355,11 +356,11 @@ KMSDRM_WaitPageFlip(_THIS, SDL_WindowData *windata) {
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/* Stay on the while loop until we get the desired event.
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We need the while the loop because we could be in a situation where:
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-We get events on the FD in time, thus not on exiting on return number 1.
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-These events are not errors, thus not exiting on return number 2.
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-These events are of POLLIN type, thus not exiting on return number 3,
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but if the event is not the pageflip we are waiting for, we arrive at the end
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of the loop and do loop re-entry, hoping the next event will be the pageflip.
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-We get and event on the FD in time, thus not on exiting on return number 1.
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-The event is not an error, thus not exiting on return number 2.
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-The event is of POLLIN type, but even then, if the event is not a pageflip,
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drmHandleEvent() won't unset wait_for_pageflip, so we have to iterate
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and go polling again.
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If it wasn't for the while loop, we could erroneously exit the function
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without the pageflip event to arrive!
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@ -368,20 +369,30 @@ KMSDRM_WaitPageFlip(_THIS, SDL_WindowData *windata) {
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means "there's data to read on the FD"), but they are not the pageflip event
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we are waiting for, so the drmEventHandle() doesn't run the flip handler, and
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since waiting_for_flip is set on the pageflip handle, it's not set and we stay
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on the loop.
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on the loop, until we get the event for the pageflip, which is fine.
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*/
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while (windata->waiting_for_flip) {
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pfd.revents = 0;
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/* poll() waits for events arriving on the FD, and returns < 0 if timeout
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passes with no events.
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We wait forever (timeout = -1), but even if we DO get an event,
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we have yet to see if it's of the required type. */
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if (poll(&pfd, 1, -1) < 0) {
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/* poll() waits for events arriving on the FD, and returns < 0 if timeout passes
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with no events or a signal occurred before any requested event (-EINTR).
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We wait forever (timeout = -1), but even if we DO get an event, we have yet
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to see if it's of the required type, then if it's a pageflip, etc */
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ret = poll(&pfd, 1, -1);
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if (ret < 0) {
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if (errno == EINTR) {
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/* poll() returning < 0 and setting errno = EINTR means there was a signal before
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any requested event, so we immediately poll again. */
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continue;
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}
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else {
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/* There was another error. Don't pull again or we could get into a busy loop. */
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SDL_LogError(SDL_LOG_CATEGORY_VIDEO, "DRM poll error");
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return SDL_FALSE; /* Return number 1. */
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}
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}
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if (pfd.revents & (POLLHUP | POLLERR)) {
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/* An event arrived on the FD in time, but it's an error. */
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@ -396,10 +407,19 @@ KMSDRM_WaitPageFlip(_THIS, SDL_WindowData *windata) {
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windata->waiting_for_flip and we will get out of the "while" loop.
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If it's not, we keep iterating on the loop. */
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KMSDRM_drmHandleEvent(viddata->drm_fd, &ev);
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} else {
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SDL_LogDebug(SDL_LOG_CATEGORY_VIDEO, "Dropping frame while waiting_for_flip");
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return SDL_FALSE; /* Return number 3. */
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}
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/* If we got to this point in the loop, we may iterate or exit the loop:
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-A legit (non-error) event arrived, and it was a POLLING event, and it was consumed
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by drmHandleEvent().
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-If it was a PAGEFLIP event, waiting_for_flip will be unset by drmHandleEvent()
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and we will exit the loop.
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-If it wasn't a PAGEFLIP, drmHandleEvent() won't unset waiting_for_flip, so we
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iterare back to polling.
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-A legit (non-error) event arrived, but it's not a POLLIN event, so it hasn't to be
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consumed by drmHandleEvent(), so waiting_for_flip isn't set and we iterate back
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to polling. */
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}
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return SDL_TRUE;
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@ -679,7 +699,7 @@ KMSDRM_DestroySurfaces(_THIS, SDL_Window *window)
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/**********************************************/
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/* Wait for last issued pageflip to complete. */
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/**********************************************/
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KMSDRM_WaitPageFlip(_this, windata);
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KMSDRM_WaitPageflip(_this, windata);
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/***********************************************************************/
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/* Restore the original CRTC configuration: configue the crtc with the */
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@ -114,7 +114,7 @@ typedef struct KMSDRM_FBInfo
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int KMSDRM_CreateSurfaces(_THIS, SDL_Window * window);
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KMSDRM_FBInfo *KMSDRM_FBFromBO(_THIS, struct gbm_bo *bo);
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KMSDRM_FBInfo *KMSDRM_FBFromBO2(_THIS, struct gbm_bo *bo, int w, int h);
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SDL_bool KMSDRM_WaitPageFlip(_THIS, SDL_WindowData *windata);
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SDL_bool KMSDRM_WaitPageflip(_THIS, SDL_WindowData *windata);
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/****************************************************************************/
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/* SDL_VideoDevice functions declaration */
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