output: add presentation refresh prediction

backend/drm/drm.c

@@ -1154,6 +1154,10 @@ void scan_drm_connectors(struct wlr_drm_backend *drm) {
 	attempt_enable_needs_modeset(drm);
 }
 
+static int mhz_to_nsec(int mhz) {
+	return 1000000000000LL / mhz;
+}
+
 static void page_flip_handler(int fd, unsigned seq,
 		unsigned tv_sec, unsigned tv_usec, void *data) {
 	struct wlr_drm_connector *conn = data;
@@ -1180,9 +1184,14 @@ static void page_flip_handler(int fd, unsigned seq,
 		.tv_sec = tv_sec,
 		.tv_nsec = tv_usec * 1000,
 	};
-	uint32_t present_flags = WLR_OUTPUT_PRESENT_VSYNC |
-		WLR_OUTPUT_PRESENT_HW_CLOCK | WLR_OUTPUT_PRESENT_HW_COMPLETION;
-	wlr_output_send_present(&conn->output, &present_time, seq, present_flags);
+	struct wlr_output_event_present present_event = {
+		.when = &present_time,
+		.seq = seq,
+		.refresh = mhz_to_nsec(conn->output.refresh),
+		.flags = WLR_OUTPUT_PRESENT_VSYNC | WLR_OUTPUT_PRESENT_HW_CLOCK |
+			WLR_OUTPUT_PRESENT_HW_COMPLETION,
+	};
+	wlr_output_send_present(&conn->output, &present_event);
 
 	if (drm->session->active) {
 		wlr_output_send_frame(&conn->output);

backend/headless/output.c

@@ -67,8 +67,9 @@ static bool output_make_current(struct wlr_output *wlr_output, int *buffer_age)
 
 static bool output_swap_buffers(struct wlr_output *wlr_output,
 		pixman_region32_t *damage) {
-	wlr_output_send_present(wlr_output, NULL, 0, 0);
-	return true; // No-op
+	// Nothing needs to be done for pbuffers
+	wlr_output_send_present(wlr_output, NULL);
+	return true;
 }
 
 static void output_destroy(struct wlr_output *wlr_output) {

backend/wayland/output.c

@@ -72,7 +72,7 @@ static bool output_swap_buffers(struct wlr_output *wlr_output,
 	}
 
 	// TODO: if available, use the presentation-time protocol
-	wlr_output_send_present(wlr_output, NULL, 0, 0);
+	wlr_output_send_present(wlr_output, NULL);
 	return true;
 }
 

backend/x11/output.c

@@ -106,7 +106,7 @@ static bool output_swap_buffers(struct wlr_output *wlr_output,
 		return false;
 	}
 
-	wlr_output_send_present(wlr_output, NULL, 0, 0);
+	wlr_output_send_present(wlr_output, NULL);
 	return true;
 }
 

include/wlr/interfaces/wlr_output.h

@@ -45,7 +45,7 @@ void wlr_output_update_enabled(struct wlr_output *output, bool enabled);
 void wlr_output_update_needs_swap(struct wlr_output *output);
 void wlr_output_damage_whole(struct wlr_output *output);
 void wlr_output_send_frame(struct wlr_output *output);
-void wlr_output_send_present(struct wlr_output *output, struct timespec *when,
-	unsigned seq, uint32_t flags);
+void wlr_output_send_present(struct wlr_output *output,
+	struct wlr_output_event_present *event);
 
 #endif

include/wlr/types/wlr_output.h

@@ -130,15 +130,28 @@ struct wlr_output_event_swap_buffers {
 };
 
 enum wlr_output_present_flag {
+	// The presentation was synchronized to the "vertical retrace" by the
+	// display hardware such that tearing does not happen.
 	WLR_OUTPUT_PRESENT_VSYNC = 0x1,
+	// The display hardware provided measurements that the hardware driver
+	// converted into a presentation timestamp.
 	WLR_OUTPUT_PRESENT_HW_CLOCK = 0x2,
+	// The display hardware signalled that it started using the new image
+	// content.
 	WLR_OUTPUT_PRESENT_HW_COMPLETION = 0x4,
+	// The presentation of this update was done zero-copy.
+	WLR_OUTPUT_PRESENT_ZERO_COPY = 0x8,
 };
 
 struct wlr_output_event_present {
 	struct wlr_output *output;
+	// Time when the content update turned into light the first time.
 	struct timespec *when;
+	// Vertical retrace counter. Zero if unavailable.
 	unsigned seq;
+	// Prediction of how many nanoseconds after `when` the very next output
+	// refresh may occur. Zero if unknown.
+	int refresh; // nsec
 	uint32_t flags; // enum wlr_output_present_flag
 };
 

rootston/output.c

@@ -855,7 +855,7 @@ static void output_handle_present(struct wl_listener *listener, void *data) {
 		.output = output->wlr_output,
 		.tv_sec = (uint64_t)output_event->when->tv_sec,
 		.tv_nsec = (uint32_t)output_event->when->tv_nsec,
-		.refresh = 0, // TODO: predict next output vsync delay
+		.refresh = (uint32_t)output_event->refresh,
 		.seq = (uint64_t)output_event->seq,
 		.flags = output_event->flags,
 	};

types/wlr_output.c

@@ -561,10 +561,17 @@ void wlr_output_schedule_frame(struct wlr_output *output) {
 		wl_event_loop_add_idle(ev, schedule_frame_handle_idle_timer, output);
 }
 
-void wlr_output_send_present(struct wlr_output *output, struct timespec *when,
-		unsigned seq, uint32_t flags) {
+void wlr_output_send_present(struct wlr_output *output,
+		struct wlr_output_event_present *event) {
+	struct wlr_output_event_present _event = {0};
+	if (event == NULL) {
+		event = &_event;
+	}
+
+	event->output = output;
+
 	struct timespec now;
-	if (when == NULL) {
+	if (event->when == NULL) {
 		clockid_t clock = wlr_backend_get_presentation_clock(output->backend);
 		errno = 0;
 		if (clock_gettime(clock, &now) != 0) {
@@ -572,16 +579,10 @@ void wlr_output_send_present(struct wlr_output *output, struct timespec *when,
 				"failed to read clock");
 			return;
 		}
-		when = &now;
+		event->when = &now;
 	}
 
-	struct wlr_output_event_present event = {
-		.output = output,
-		.when = when,
-		.seq = seq,
-		.flags = flags,
-	};
-	wlr_signal_emit_safe(&output->events.present, &event);
+	wlr_signal_emit_safe(&output->events.present, event);
 }
 
 bool wlr_output_set_gamma(struct wlr_output *output, size_t size,

types/wlr_presentation_time.c

@@ -42,8 +42,8 @@ static void feedback_send_presented(struct wlr_presentation_feedback *feedback,
 	uint32_t seq_hi = event->seq >> 32;
 	uint32_t seq_lo = event->seq & 0xFFFFFFFF;
 	wp_presentation_feedback_send_presented(feedback->resource,
-		tv_sec_hi, tv_sec_lo, event->tv_nsec, event->refresh, seq_hi, seq_lo,
-		event->flags);
+		tv_sec_hi, tv_sec_lo, event->tv_nsec, event->refresh,
+		seq_hi, seq_lo, event->flags);
 
 	wl_resource_destroy(feedback->resource);
 }