Don't fetch lots of axes state information for rendering if object is not visible. * gl-render.cc (opengl_renderer::draw_axes_planes): Check axes color and visibility and return immediately from function if there is nothing to do. * gl-render.cc (opengl_renderer::draw_axes_boxes): Check axes visibility and return immediately from function if there is nothing to do. * gl-render.cc (opengl_renderer::draw_axes_x_grid, drax_axes_y_grid, draw_axes_z_grid): Check axes state and visibility before bothering to fetch any more state data. * gl-render.cc (miscellaneous): Clean up comments. Change lines to wrap at < 80 chars. * graphics.cc (axes::properties::update_axes_layout): Use std::swap instead of intermediate temporary variable for clearer coding style.

## The `oregonator'.
##
## Reference:
##
##   Oscillations in chemical systems.  IV.  Limit cycle behavior in a
##   model of a real chemical reaction. Richard J. Field and Richard
##   M. Noyes, The Journal of Chemical Physics, Volume 60 Number 5,
##   March 1974.

function dx = oregonator (x, t)

  dx = zeros (3, 1);

  dx(1) = 77.27*(x(2) - x(1)*x(2) + x(1) - 8.375e-06*x(1)^2);
  dx(2) = (x(3) - x(1)*x(2) - x(2)) / 77.27;
  dx(3) = 0.161*(x(1) - x(3));

end