output: add presented flag to presentation event

backend/drm/drm.c

@@ -1465,6 +1465,7 @@ static void handle_page_flip(int fd, unsigned seq,
 		/* The DRM backend guarantees that the presentation event will be for
 		 * the last submitted frame. */
 		.commit_seq = conn->output.commit_seq,
+		.presented = true,
 		.when = &present_time,
 		.seq = seq,
 		.refresh = mhz_to_nsec(conn->output.refresh),

backend/headless/output.c

@@ -66,6 +66,7 @@ static bool output_commit(struct wlr_output *wlr_output) {
 	if (wlr_output->pending.committed & WLR_OUTPUT_STATE_BUFFER) {
 		struct wlr_output_event_present present_event = {
 			.commit_seq = wlr_output->commit_seq + 1,
+			.presented = true,
 		};
 		wlr_output_send_present(wlr_output, &present_event);
 	}

backend/wayland/output.c

@@ -75,6 +75,7 @@ static void presentation_feedback_handle_presented(void *data,
 	};
 	struct wlr_output_event_present event = {
 		.commit_seq = feedback->commit_seq,
+		.presented = true,
 		.when = &t,
 		.seq = ((uint64_t)seq_hi << 32) | seq_lo,
 		.refresh = refresh_ns,
@@ -91,6 +92,7 @@ static void presentation_feedback_handle_discarded(void *data,
 
 	struct wlr_output_event_present event = {
 		.commit_seq = feedback->commit_seq,
+		.presented = false,
 	};
 	wlr_output_send_present(&feedback->output->wlr_output, &event);
 
@@ -350,6 +352,7 @@ static bool output_commit(struct wlr_output *wlr_output) {
 		} else {
 			struct wlr_output_event_present present_event = {
 				.commit_seq = wlr_output->commit_seq + 1,
+				.presented = true,
 			};
 			wlr_output_send_present(wlr_output, &present_event);
 		}

backend/x11/output.c

@@ -690,9 +690,11 @@ void handle_x11_present_event(struct wlr_x11_backend *x11,
 			flags |= WLR_OUTPUT_PRESENT_ZERO_COPY;
 		}
 
+		bool presented = complete_notify->mode != XCB_PRESENT_COMPLETE_MODE_SKIP;
 		struct wlr_output_event_present present_event = {
 			.output = &output->wlr_output,
 			.commit_seq = complete_notify->serial,
+			.presented = presented,
 			.when = &t,
 			.seq = complete_notify->msc,
 			.flags = flags,

include/wlr/types/wlr_output.h

@@ -228,6 +228,8 @@ struct wlr_output_event_present {
 	// Frame submission for which this presentation event is for (see
 	// wlr_output.commit_seq).
 	uint32_t commit_seq;
+	// Whether the frame was presented at all.
+	bool presented;
 	// Time when the content update turned into light the first time.
 	struct timespec *when;
 	// Vertical retrace counter. Zero if unavailable.

types/wlr_output.c

@@ -959,8 +959,8 @@ void wlr_output_send_present(struct wlr_output *output,
 	assert(event);
 	event->output = output;
 
-	struct timespec now;
-	if (event->when == NULL) {
+	if (event->presented && event->when == NULL) {
+		struct timespec now;
 		clockid_t clock = wlr_backend_get_presentation_clock(output->backend);
 		errno = 0;
 		if (clock_gettime(clock, &now) != 0) {