Tile_coord t, Tile_coord c
Game_window *gwin, Game_object *obj, int xtiles, int ytiles, Tile_coord c
inline Tile_coord Rotate90r	(	Tile_coord t,			// Tile to move.	Tile_coord c			// Center to rotate around.	)	{					// Get cart. coords. rel. to center.	int rx = t.tx - c.tx, ry = c.ty - t.ty;	return Tile_coord(c.tx + ry, c.ty + rx, t.tz);	}