presentation_feedback: add the sampled state

include/wlr/types/wlr_presentation_time.h

@@ -31,9 +31,15 @@ struct wlr_presentation_feedback {
 	struct wl_resource *resource;
 	struct wlr_presentation *presentation;
 	struct wlr_surface *surface;
-	bool committed;
 	struct wl_list link; // wlr_presentation::feedbacks
 
+	// The surface contents were committed.
+	bool committed;
+	// The surface contents were sampled by the compositor and are to be
+	// presented on the next flip. Can become true only after committed becomes
+	// true.
+	bool sampled;
+
 	struct wl_listener surface_commit;
 	struct wl_listener surface_destroy;
 };
@@ -55,5 +61,7 @@ void wlr_presentation_destroy(struct wlr_presentation *presentation);
 void wlr_presentation_send_surface_presented(
 	struct wlr_presentation *presentation, struct wlr_surface *surface,
 	struct wlr_presentation_event *event);
+void wlr_presentation_surface_sampled(
+	struct wlr_presentation *presentation, struct wlr_surface *surface);
 
 #endif

types/wlr_presentation_time.c

@@ -61,8 +61,10 @@ static void feedback_handle_surface_commit(struct wl_listener *listener,
 		wl_container_of(listener, feedback, surface_commit);
 
 	if (feedback->committed) {
-		// The content update has been superseded
-		feedback_send_discarded(feedback);
+		if (!feedback->sampled) {
+			// The content update has been superseded
+			feedback_send_discarded(feedback);
+		}
 	} else {
 		feedback->committed = true;
 	}
@@ -216,8 +218,20 @@ void wlr_presentation_send_surface_presented(
 	struct wlr_presentation_feedback *feedback, *feedback_tmp;
 	wl_list_for_each_safe(feedback, feedback_tmp,
 			&presentation->feedbacks, link) {
-		if (feedback->surface == surface && feedback->committed) {
+		if (feedback->surface == surface && feedback->sampled) {
 			feedback_send_presented(feedback, event);
 		}
 	}
 }
+
+void wlr_presentation_surface_sampled(
+		struct wlr_presentation *presentation, struct wlr_surface *surface) {
+	// TODO: maybe use a hashtable to optimize this function
+	struct wlr_presentation_feedback *feedback, *feedback_tmp;
+	wl_list_for_each_safe(feedback, feedback_tmp,
+			&presentation->feedbacks, link) {
+		if (feedback->surface == surface && feedback->committed) {
+			feedback->sampled = true;
+		}
+	}
+}