output-damage: add wlr_output_damage_step

This does the same as wlr_output_damage_attach_render except it
doesn't call wlr_output_attach_render.

Author: emersion

include/wlr/types/wlr_output_damage.h

@@ -76,6 +76,13 @@ void wlr_output_damage_destroy(struct wlr_output_damage *output_damage);
  */
 bool wlr_output_damage_attach_render(struct wlr_output_damage *output_damage,
 	bool *needs_frame, pixman_region32_t *buffer_damage);
+/**
+ * Advance the output damage state machine. Takes the buffer age as input,
+ * returns a bool indicating whether rendering a new frame is necessary and the
+ * accumulated damage.
+ */
+void wlr_output_damage_step(struct wlr_output_damage *output_damage,
+	int buffer_age, bool *needs_frame, pixman_region32_t *buffer_damage);
 /**
  * Accumulates damage and schedules a `frame` event.
  */

types/wlr_output_damage.c

@@ -150,6 +150,14 @@ bool wlr_output_damage_attach_render(struct wlr_output_damage *output_damage,
 		return false;
 	}
 
+	wlr_output_damage_step(output_damage, buffer_age, needs_frame, damage);
+	return true;
+}
+
+void wlr_output_damage_step(struct wlr_output_damage *output_damage,
+		int buffer_age, bool *needs_frame, pixman_region32_t *damage) {
+	struct wlr_output *output = output_damage->output;
+
 	*needs_frame =
 		output->needs_frame || pixman_region32_not_empty(&output_damage->current);
 	// Check if we can use damage tracking
@@ -178,8 +186,6 @@ bool wlr_output_damage_attach_render(struct wlr_output_damage *output_damage,
 				extents->x2 - extents->x1, extents->y2 - extents->y1);
 		}
 	}
-
-	return true;
 }
 
 void wlr_output_damage_add(struct wlr_output_damage *output_damage,