Set needs_swap on output when gamma changes

backend/drm/drm.c

@@ -232,10 +232,15 @@ static void wlr_drm_connector_set_gamma(struct wlr_output *output,
 		uint32_t size, uint16_t *r, uint16_t *g, uint16_t *b) {
 	struct wlr_drm_connector *conn = (struct wlr_drm_connector *)output;
 	struct wlr_drm_backend *drm = (struct wlr_drm_backend *)output->backend;
+	bool ok;
 
 	if (conn->crtc) {
-		drm->iface->crtc_set_gamma(drm, conn->crtc, r, g, b, size);
+		ok = drm->iface->crtc_set_gamma(drm, conn->crtc, r, g, b, size);
+		if (ok) {
+			wlr_output_update_needs_swap(output);
+		}
 	}
+
 }
 
 static uint32_t wlr_drm_connector_get_gamma_size(struct wlr_output *output) {