Every now and then, a user asks whether it is possible to make an entire Matlab window transparent (example ^[1]). This could be used, for example, for window fade-in/fade-out effects. The short answer is that there is no supported way of doing this with pure documented Matlab, but it is trivially easy to achieve using just a bit of Java magic powder (surprise, surprise).

Matlab figure window transparency

Following an idea I got from Malcolm Lidierth’s MUtilities ^[2] submission on the Matlab File Exchange, the solution for setting Matlab figure window transparency is quite simple: Get the figure’s underlying Java window reference handle, as in last week’s ^[3] article. Then use Java’s setWindowOpacity method ^[4] to set the window’s transparency value. Actually, setWindowOpacity sets the opacity level, rather than transparency, but they are obviously complementary and I personally find “transparency” to be more easily understandable.
By default, windows are created with an opacity of 1.0 (= not transparent). They can be set to any floating-point value between 0.0-1.0, where an opacity of 0.0 means full transparency, and any value in between means partial transparency (i.e., translucency):

jFigPeer = get(handle(gcf),'JavaFrame');
jWindow = jFigPeer.fFigureClient.getWindow;
com.sun.awt.AWTUtilities.setWindowOpacity(jWindow,0.7)

^[5]

jDesktop = com.mathworks.mde.desk.MLDesktop.getInstance.getMainFrame;
com.sun.awt.AWTUtilities.setWindowOpacity(jDesktop, 0.8);

Note that the com.sun.awt.AWTUtilities class also enables other GUI effects ^[6] that would make a Matlab GUI developer’s mouth to start drooling: shaped windows, per-pixel transparency values, mirroring/reflection, window shadows, gradients ^[7] etc. Perhaps I’ll explore their adaptation for Matlab figures someday.

Fade-in / fade-out

Window fade-in/fade-out effects can easily be achieved using transparency: Simply invoke the setWindowOpacity method several times, with progressively higher or lower values. This is easily done in a simple blocking loop. For example, to fade-out a window:

for stepIdx = 1 : 5
   newAlpha = 1.0 - 0.2*stepIdx;
   com.sun.awt.AWTUtilities.setWindowOpacity(jWindow,newAlpha);
   jWindow.repaint;
   pause(0.2);  % seconds
end

% Compute the required opacity-setting steps
fadeDuration = 1.5;  % seconds
oldAlpha = com.sun.awt.AWTUtilities.getWindowOpacity(jWindow);
newAlpha = 0.0;
deltaAlpha = newAlpha - oldAlpha;
maxStepAlpha = 0.03;
steps = fix(abs(deltaAlpha) / maxStepAlpha) + 1;
stepAlpha = deltaAlpha / steps;
stepDuration = fadeDuration / (steps-1);
% If blocking, do the fade effect immediately
if blockingFlag || steps==1
   for stepIdx = 1 : steps
      newAlpha = oldAlpha + stepAlpha*stepIdx;
      com.sun.awt.AWTUtilities.setWindowOpacity(jWindow,newAlpha);
      jWindow.repaint;
      if stepIdx < steps,  pause(stepDuration);  end
   end
else
   % non-blocking: fade in/out asynchronously using a dedicated timer
   start(timer('ExecutionMode','fixedRate', 'Period',0.1, 'TasksToExecute',steps, ...
               'TimerFcn', {@timerFcn,jWindow,oldAlpha,stepAlpha}));
end
% Timer function for non-blocking fade-in/fade-out effect
function timerFcn(hTimer,eventData,jFrame,currentAlpha,stepAlpha)  %#ok eventData
  stepIdx = hTimer.TasksExecuted;
  newAlpha = currentAlpha + stepAlpha*stepIdx;
  com.sun.awt.AWTUtilities.setWindowOpacity(jFrame,newAlpha);
  jFrame.repaint;
  if stepIdx == hTimer.TasksToExecute
      stop(hTimer);
      delete(hTimer);
  end
end  % timerFcn

Of course, you can also fade-in/out to intermediate values such as 0.3 or 0.8. If you fade-out completely (i.e., to a value of 0.0), it might be a good idea to actually close the figure window once it gets the totally-transparent value of 0.0.
I’ve prepared a Matlab utility that contains all these options, including optional blocking/non-blocking fade effects, in my setFigTransparency utility ^[8], which is available for download on the Matlab File Exchange. You may also wish to use Malcolm Lidierth’s MUtilities ^[2], which also has similar functionalities (plus some other goodies).

Limitations

Setting a figure window’s transparency requires using Java Run-time Engine (JRE) 1.6.0_10 (also called “Java 6 update 10”) or higher. This means that it’s supported on Matlab release 7.9 (R2009b) and higher by default, and on earlier releases using a JRE retrofit.
If you are using an earlier Matlab release, consider a retrofit of JRE 1.6.0_10 or any later version (e.g., the latest available version today is 1.6 update 24). The JRE can be downloaded from here ^[9], and you can configure Matlab to use it according to the instructions here ^[10]. As noted, Matlab R2009b (7.9) and onward, at least on Microsoft Windows, pre-bundle a JRE version that does support transparency/opacity and so do not require a retrofit.
You can check your current Java version in Matlab as follows:

>> version -java
ans =
Java 1.6.0_17-b04 with Sun Microsystems Inc. Java HotSpot(TM) Client VM mixed mode

Unfortunately, Matlab plot axes cannot be made transparent. If you have any axes in your GUI, the axes area will simply appear as a shaded axes, whose intensity depends on the selected alpha (transparency) value; the contents beneath the window will not be merged in the axes area as it is in the non-axes areas.
Finally, note that com.sun.awt.AWTUtilities is itself an undocumented Java class. It is bundled with the standard Java release since 2008 (1.6.0_10), and yet is not part of the official release because its API has not yet settled. In fact, in the upcoming Java 7 release, which is expected in a few months, and which I expect to be available in Matlab sometime in 2012, the set of transparency/opacity methods have migrated ^[11] to the fully-documented java.awt.Window class.

Blurred figure window

So here’s a riddle for you: using figure window transparency, can you guess how to make a Matlab figure appear blurred for disabled figures ^[3] (see the screenshot there)? There are several possible ways to do this – can you find the simplest? The first one to post a comment ^[12] with a correct answer gets a smiley… My answer will appear in next week’s article.

Upgraded website

Also, did you notice my new website design? It’s supposed to be much more readable (yes – also on Android ^[13]…). It now also runs on a multi-server cloud, which means more stability and faster response times. Do you like the new design? hate it? I would love to hear your feedback via comment ^[12] or email ^[14].

18 Comments To "Transparent Matlab figure window"

#1 Comment By Brant A Jameson On April 14, 2011 @ 14:30

#2 Comment By Jan Simon On April 15, 2011 @ 06:03

#3 Comment By Mory On April 15, 2011 @ 11:46

function blurwindow(fnum)
%BLURWINDOW  Blurs a given window.
%    BLURWINDOW Blurs the current window
%    BLURWINDOW(FNUM) blurs the given window.
%
%    BLURWINDOW clear REMOVES THE BLUR

%Use a consistent, random figure number
FNUMBLUR = 1636033446;

%Input handling 
if nargin < 1
    fnum = gcf;
elseif ischar(fnum) && strcmpi(fnum,'clear')
    if ishandle(FNUMBLUR)
        close(FNUMBLUR);
    end
    return;
end

%Find the position of the figure to be blurred
figPos = get(fnum,'position');
figUnits = get(fnum,'units');

%Setup the overlay figure
figure(FNUMBLUR);
set(FNUMBLUR,'units',figUnits);
set(FNUMBLUR,'position',figPos);
set(FNUMBLUR,'NumberTitle','off';
drawnow;

%Make the overlay semi-transparent
jFigPeer = get(handle(FNUMBLUR),'JavaFrame');
jWindow = jFigPeer.fFigureClient.getWindow;
com.sun.awt.AWTUtilities.setWindowOpacity(jWindow,0.8)

#4 Comment By Yair Altman On April 16, 2011 @ 10:51

#5 Pingback By Controlling callback re-entrancy | Undocumented Matlab On August 10, 2011 @ 11:04

#6 Comment By Alex On April 20, 2012 @ 10:01

#7 Comment By Yair Altman On April 21, 2012 @ 10:27

#8 Comment By Malcolm Lidierth On April 22, 2012 @ 08:10

#9 Comment By julien On June 23, 2012 @ 07:45

#10 Comment By Yair Altman On June 23, 2012 @ 11:40

#11 Comment By Dirk Engel On March 25, 2013 @ 04:06

#12 Comment By Yair Altman On March 25, 2013 @ 04:21

#13 Pingback By ScreenCapture utility | Undocumented Matlab On January 28, 2013 @ 08:14

#14 Comment By Martin Höcker On June 12, 2013 @ 08:50

jFigPeer = get(handle(gcf),'JavaFrame');
jWindow = jFigPeer.fHG1Client.getWindow;
com.sun.awt.AWTUtilities.setWindowOpacity(jWindow,0.7)

#15 Comment By Yair Altman On June 12, 2013 @ 09:42

#16 Comment By Malcolm Lidierth On June 12, 2013 @ 19:10

#17 Comment By Razvan On September 7, 2013 @ 16:58

#18 Comment By Yair Altman On September 7, 2013 @ 21:58