Graphics

Example -- Using newplot

To illustrate the use of newplot, this example creates a function that is similar to the built-in plot function, except it automatically cycles through different line styles instead of using different colors for multiline plots.

• function my_plot(x,y)
  cax = newplot; % newplot returns handle of current axes
  LSO = ['- ';'--';': ';'-.'];
  set(cax,'FontName','Times','FontAngle','italic') 
  set(get(cax,'Parent'),'MenuBar','none') % 
  line_handles = line(x,y,'Color','b');
  style = 1;
  for i = 1:length(line_handles)
      if style > length(LSO), style = 1;end
      set(line_handles(i),'LineStyle',LSO(style,:))
      style = style + 1;
  end
  grid on
  

The function my_plot uses the high-level line function syntax to plot the data. This provides the same flexibility in input argument dimension that the built-in plot function supports. The line function does not check the value of the figure or axes NextPlot property. However, because my_plot calls newplot, it behaves the same way the high-level plot function does - with default values in place, my_plot clears and resets the axes each time you call it.

my_plot uses the handle returned by newplot to access the target figure and axes. This example sets axes font properties and disables the figure's menu bar. Note how the figure handle is obtained via the axes Parent property.

This picture shows typical output for the my_plot function.

• my_plot(1:10,peaks(10))
  
  
  

Basic Plotting M-file Structure

This example illustrates the basic structure of graphics M-files:

• Call newplot early to conform to the NextPlot properties and to obtain the handle of the target axes.
• Reference the axes handle returned by newplot to set any axes properties or to obtain the figure's handle.
• Call object creation functions to draw graphics objects with the desired characteristics.

The MATLAB default settings for the NextPlot properties facilitate writing M-files that adhere to the standard behavior: reuse the figure window, but clear and reset the axes with each new graph. Other values for these properties allow you to implement different behaviors.

Replacing Only the Children Objects -- replacechildren

The replacechildren value for NextPlot causes newplot to remove child objects from the figure or axes, but does not reset any property values (except the list of handles contained in the Children property).

This can be useful after setting properties you want to use for subsequent graphs without having to reset properties. For example, if you type on the command line

• set(gca,'ColorOrder',[0 0 1],'LineStyleOrder','-|--|:|-.',...
          'NextPlot','replacechildren')
  plot(x,y)
  

plot produces the same output as the M-file my_plot in the previous section, but only within the current axes. Calling plot still erases the existing graph (i.e., deletes the axes children), but it does not reset axes properties. The values specified for the ColorOrder and LineStyleOrder properties remain in effect.

Targeting Graphics Output with newplot

Testing for Hold State