Graphics

Testing for Hold State

There are situations in which your M-file should change the visual appearance of the axes to accommodate new graphics objects. For example, if you want the M-file my_plot from the previous example to accept 3-D data, it makes sense to set the view to 3-D when the input data has z-coordinates.

However, to be consistent with the behavior of the MATLAB high-level routines, it is a good practice to test if hold is on before changing parent axes or figure properties. When hold is on, the axes and figure NextPlot properties are both set to add.

The M-file, my_plot3, accepts 3-D data and also checks the hold state, using ishold, to determine if it should change the view.

• function my_plot3(x,y,z)
  cax = newplot;
  hold_state = ishold; % ishold tests the current hold state
  LSO = ['- ';'--';': ';'-.'];
  if nargin == 2
      hlines = line(x,y,'Color','k');
      if ~hold_state % Change view only if hold is off
          view(2)
      end
  elseif nargin == 3
      hlines = line(x,y,z,'Color','k');
      if ~hold_state % Change view only if hold is off
          view(3)
      end
  end
  ls = 1;
  for hindex = 1:length(hlines)
      if ls > length(LSO),ls = 1;end
      set(hlines(hindex),'LineStyle',LSO(ls,:))
      ls = ls + 1;
  end
  

If hold is on when you call my_plot3, it does not change the view. If hold is off, my_plot3 sets the view to 2-D or 3-D, depending on whether there are two or three input arguments.

Example -- Using newplot

Protecting Figures and Axes