output: send present event from all backends

backend/headless/output.c

@@ -67,6 +67,7 @@ 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
 }
 

backend/wayland/output.c

@@ -66,8 +66,14 @@ static bool output_swap_buffers(struct wlr_output *wlr_output,
 	output->frame_callback = wl_surface_frame(output->surface);
 	wl_callback_add_listener(output->frame_callback, &frame_listener, output);
 
-	return wlr_egl_swap_buffers(&output->backend->egl, output->egl_surface,
+	if (!wlr_egl_swap_buffers(&output->backend->egl,
-		damage);
+			output->egl_surface, damage)) {
+		return false;
+	}
+
+	// TODO: if available, use the presentation-time protocol
+	wlr_output_send_present(wlr_output, NULL, 0, 0);
+	return true;
 }
 
 static void output_transform(struct wlr_output *wlr_output,

backend/x11/output.c

@@ -102,7 +102,12 @@ static bool output_swap_buffers(struct wlr_output *wlr_output,
 	struct wlr_x11_output *output = (struct wlr_x11_output *)wlr_output;
 	struct wlr_x11_backend *x11 = output->x11;
 
-	return wlr_egl_swap_buffers(&x11->egl, output->surf, damage);
+	if (!wlr_egl_swap_buffers(&x11->egl, output->surf, damage)) {
+		return false;
+	}
+
+	wlr_output_send_present(wlr_output, NULL, 0, 0);
+	return true;
 }
 
 static const struct wlr_output_impl output_impl = {

types/wlr_output.c

@@ -18,6 +18,8 @@
 
 #define OUTPUT_VERSION 3
 
+#define DEFAULT_PRESENT_CLOCK CLOCK_MONOTONIC
+
 static void output_send_to_resource(struct wl_resource *resource) {
 	struct wlr_output *output = wlr_output_from_resource(resource);
 	const uint32_t version = wl_resource_get_version(resource);
@@ -562,6 +564,16 @@ void wlr_output_schedule_frame(struct wlr_output *output) {
 
 void wlr_output_send_present(struct wlr_output *output, struct timespec *when,
 		unsigned seq, uint32_t flags) {
+	struct timespec now;
+	if (when == NULL) {
+		if (!clock_gettime(DEFAULT_PRESENT_CLOCK, &now)) {
+			wlr_log_errno(WLR_ERROR, "failed to send output present event: "
+				"failed to read clock");
+			return;
+		}
+		when = &now;
+	}
+
 	struct wlr_output_event_present event = {
 		.output = output,
 		.when = when,