Certain properties have dependencies on the value of other properties. MATLAB® automatically calculates the values of these properties and updates their values based on the current graphics model. For example, axis limits affect the values used for axis ticks, which, in turn, affect the axis tick labels.
When you query a calculated property, MATLAB performs an
drawnow to ensure all property values
are up to date before returning the property value. The query causes
a full update of all dependent properties and an update of the screen.
MATLAB calculates the values of certain properties based on other values on which that property depends. For example, plotting functions automatically create an axes with axis limits, tick labels, and a size appropriate for the plotted data and the figure size.
MATLAB graphics performs a full update, if necessary, before returning a value from a calculated property to ensure the returned value is up to date.
|Object||Automatically Calculated Properties|
When you set property values, you change the state of the graphics model and mark it as needing to be updated. When you query an autocalculated property, MATLAB needs to perform an update if the graphics model and graphics hardware are not in sync.
When you get and set properties in the same loop, you can create a situation where updates are performed with every pass through the loop.
get causes an update.
set marks the graphics model
as needing an update.
The cycle is repeated with each pass through the loop. It is better to execute all property queries in one loop, then execute all property sets in another loop, as shown in the following example.
This example gets and sets the text
|Code with Poor Performance||Code with Better Performance|
h = gobjects(1,500); p = zeros(500,3); for ix = 1:500 h(ix) = text(ix/500,ix/500,num2str(ix)); end drawnow % Gets and sets in the same loop, % prompting a full update at each pass for ix = 1:500 pos = get(h(ix),'Position'); ext = get(h(ix),'Extent'); p(ix,:) = [pos(1)+(ext(3)+ext(1)), ... pos(2)+ext(2)+ext(4),0]; set(h(ix),'Position',p(ix,:)) end drawnow
h = gobjects(1,500); p = zeros(500,3); for ix = 1:500 h(ix) = text(ix/500,ix/500,num2str(ix)); end drawnow % Get and save property values for ix=1:500 pos = get(h(ix),'Position'); ext = get(h(ix),'Extent'); p(ix,:) = [pos(1)+(ext(3)+ext(1)), ... pos(2)+ext(2)+ext(4),0]; end % Set the property values and % call a drawnow after the loop for ix=1:500 set(h(ix),'Position',p(ix,:)); end drawnow
This code performs poorly because:
The performance is better because this code:
Extentto Rotate Labels