feat(scenery): models laid along curves (sweep nodes), bent to follow the paths or repeated along them, loaded and saved with the scenery; trainsets put on a path while the simulation runs; trainset turned around by reversed after its header: the first vehicle stays at the offset and leads towards point 1, the rest stands behind it; launcher keeps reversed trainsets and can turn one around; memory cells saved with the new name of the path they name; events tell their targets and the events of a multiple event; renderer tells whether the cursor is over a surface; vehicle placed in the editor entered when the driving goes on

rendering/renderer.h

@@ -73,6 +73,7 @@ public:
     virtual auto Pick_Node() const -> scene::basic_node const * = 0;
 
     virtual auto Mouse_Position() const -> glm::dvec3 = 0;
+    virtual auto Mouse_Hit() const -> bool { return true; }
     // editor helpers: matrices/position of the most recent color pass camera.
     // the view matrix is camera-relative (rotation only, camera at origin), matching the
     // camera-relative rendering used by the engine; build object matrices relative to Camera_Position().