world_vertex = model_matrix*vertex;
world_look_dir = normalize(world_vertex.xyz-inverse(view_matrix)[3].xyz);
gl_Position = proj_matrix*view_matrix*world_vertex;
world_vertex = model_matrix*vertex;
world_look_dir = normalize(world_vertex.xyz-inverse(view_matrix)[3].xyz);
gl_Position = proj_matrix*view_matrix*world_vertex;