Graphics

Saving Handles in M-Files

Graphics M-files frequently use handles to access property values and to direct graphics output to a particular target. MATLAB provides utility routines that return the handles to key objects (such as the current figure and axes). In M-files, however, these utilities may not be the best way to obtain handles because:

• Querying MATLAB for the handle of an object or other information is less efficient than storing the handle in a variable and referencing that variable.
• The current figure, axes, or object may change during M-file execution because of user interaction.

Save Information First

It is a good practice to save relevant information about the MATLAB state in the beginning of your M-file. For example, you can begin an M-file with

• cax = newplot;
  cfig = get(cax,'Parent');
  hold_state = ishold;
  

rather than querying this information each time you need it. Remember that utility commands like ishold obtain the values they return whenever called. (The ishold command issues a number of get commands and string compares (strcmp) to determine the hold state.)

If you are temporarily going to alter the hold state within the M-file, you should save the current values of the NextPlot properties so you can reset them later.

• ax_nextplot = lower(get(cax,'NextPlot'));
  fig_nextplot = lower(get(cfig,'NextPlot'));
  .
  .
  .
  set(cax,'NextPlot',ax_nextplot)
  set(cfig,'NextPlot',fig_nextplot)
  

Handle Validity Versus Handle Visibility

Properties Changed by Built-In Functions