gamma-control-v1: add wlr_gamma_control_manager_v1_get_control()

include/wlr/types/wlr_gamma_control_v1.h

@@ -39,5 +39,7 @@ struct wlr_gamma_control_v1 {
 
 struct wlr_gamma_control_manager_v1 *wlr_gamma_control_manager_v1_create(
 	struct wl_display *display);
+struct wlr_gamma_control_v1 *wlr_gamma_control_manager_v1_get_control(
+	struct wlr_gamma_control_manager_v1 *manager, struct wlr_output *output);
 
 #endif

types/wlr_gamma_control_v1.c

@@ -207,13 +207,10 @@ static void gamma_control_manager_get_gamma_control(struct wl_client *client,
 		return;
 	}
 
-	struct wlr_gamma_control_v1 *gc;
+	if (wlr_gamma_control_manager_v1_get_control(manager, output) != NULL) {
-	wl_list_for_each(gc, &manager->controls, link) {
-		if (gc->output == output) {
 		zwlr_gamma_control_v1_send_failed(resource);
 		return;
 	}
-	}
 
 	struct wlr_gamma_control_v1 *gamma_control =
 		calloc(1, sizeof(struct wlr_gamma_control_v1));
@@ -299,3 +296,14 @@ struct wlr_gamma_control_manager_v1 *wlr_gamma_control_manager_v1_create(
 
 	return manager;
 }
+
+struct wlr_gamma_control_v1 *wlr_gamma_control_manager_v1_get_control(
+		struct wlr_gamma_control_manager_v1 *manager, struct wlr_output *output) {
+	struct wlr_gamma_control_v1 *gamma_control;
+	wl_list_for_each(gamma_control, &manager->controls, link) {
+		if (gamma_control->output == output) {
+			return gamma_control;
+		}
+	}
+	return NULL;
+}