The Win32::GUI FAQ

Aldo Calpini,
Erick Bourgeois, 
Felix Gaehler,
v0.3, August 20, 2001

This is the "Frequently Asked Questions" for Perl Win32::GUI module. The questions and answers have been collected from the Win32::GUI-Users mailing list.

General Questions

What is Win32::GUI?

"Win32::GUI is a Win32-platform native graphical user interface toolkit for Perl. Basically, it's an XS implementation of most of the functions found in user32.dll and gdi32.dll, with an object oriented Perl interface and an event-based dialog model that mimic the functionality of visual basic. It was a big fun for me to put it up, hope it will be a fun for you too :-)"

Where can I get Win32::GUI?

The creator and chief maintainer of the Win32::GUI module is Aldo Calpini. The module and pertinent information can be found at
"The module is actually in beta testing so be warned that syntax and behavior can change with future builds; and of course, that there are many incomplete parts, sparse documentation (you can browse here the work in progress), and generally a lot of things to do."

Win32::GUI for ActiveState Perl 5.6 can be downloaded from the ActiveState Archive using PPM:

  ppm install Win32::GUI

Documentation is available at

What about licensing?

If I develop a product in Perl with usage of the Win32::GUI module, and I spread (well lets assume for FREE) to the public.. Is it still under GNU license or do we have to pay the Win32::GUI team something ?

"No, you don't have to pay anything. I'm not a lawyer and I don't want to pay a lawyer :-) Win32::GUI is released under the Artistic License, e.g. you can redistribute it under the same terms of Perl itself."

Frequent Problems

Why does my window seem to freeze when my program is in a loop?

I can help here. Put a call to DoEvents() inside the loop. This will ensure that all queued messages are processed before going on with the loop:

use strict;
use Win32::GUI;

my $main = Win32::GUI::Window->new(
  -name    => "Main",
  -title   => "Win32-GUI: Doevents-Demo",
  -left    => 100,
  -top     => 100,
  -width   => 600,
  -height  => 400,

sub Main_Terminate() {
  print "Main window terminated\n";
  return -1;

my $textfield = $main->AddTextfield(
  -name   => "Textfield",
  -text   => "have fun and more",
  -left   => 75,
  -top    => 150,
  -width  => 200,
  -height => 40,
  -readonly => 1,


$textfield->Text("Processing infile...");
open INFILE, "<infile.txt" or die "open infile error: $!";
my $linenr = 0;
foreach my $line (<INFILE>) {
  $textfield->Text("Processing line $linenr");
  Win32::GUI::DoEvents() >= 0 or die "Window was closed during processing";
  sleep 1; #body of the loop...

sleep 1; #program continues...

This will, of course, make your loop run slightly slower (almost irrelevant if there is no activity on the window). But there is the advantage (other than having the Textfield saying "Processing...") of being able to stop the loop in the middle by killing the window, or with a 'dedicated' stopbutton, for example.

Can I use a window handle in more than one process?

If you run some lengthy processing like web page retrieval with LWP, database search, file processing etc., and you cannot call $Window->DoEvents() within that processing, your window will seem to freeze during your processing. The solution to that is, to do the processing in a separate Windows thread or process. ActivePerl 5.6 simulates the "fork" command using Windows threads.

"Well, from Windows point of view, it is a thread. From Perl's point of view, it is a process. The Perl interpreter is busily keeping the data separate between the two threads (I'm not sure I understand the complete technique of the magic that does that, but I'm sure it can be made to work because the Perl language doesn't expose "real" addresses (much))."

"On the other hand, the (UNIX) model for "fork" is that the multiple processes (threads on Perl for Windows) start off with identical data/variables/file handles. And the Windows model for "windows" is that the windows are owned by a process (not a thread), and can be accessed by any thread that has the window handle. (And in fact, because Windows was developed on DOS, the windows are even a bit visible to other processes, but that doesn't concern us here.)"

"By creating the Win32::GUI objects before forking, both the parent and child threads get copies (?) of the object variables. Because of the nature of Windows, the embedded Window handles inside both copies of the object variables are equally usable. Because of the (present) nature of Win32::GUI, whereby most of the parameter data is pumped into Win32 API parameters, and most of the return values are obtained by calling Win32 APIs to obtain it, I have shown experimentally that it is possible to use the Win32::GUI object references from both a parent and a child thread. Now it is important to remember that Windows only delivers window messages to the first thread of a program, so in the Perl "fork" environment, this gets translated to only the parent process of a group of Perl-forked processes can successfully run Win32::GUI::Dialog (Yep, I tried it the other way first, figuring that the parent could more easily monitor the child process for death, since fork returns the child pid, and waitpid works that way--but it just hung, and the windows never appeared). However, the child can use the object references created by Win32::GUI [before the fork] to access the "IsEnabled", "IsVisible" attributes of the window widgets, and they are dynamically updated (not cached in the object). The child can access the current selection from combo boxes. The child can enable and disable widgets, and the display gets updated appropriately. This is quite adequate for my application, which now can do its "long" operations in the child "process", and keep the GUI window "active" (except that certain parts get disabled during "long" operations)."

How can I use Win32::GUI functions in EVAL?

Yes, Win32::GUI supports things like these (it's really Perl that supports it :-), but you need to escape your window-handler variable $W:

    eval qq (
        sub main::$subtxt {
            print "button clicked\n";
            \$W->SimpleLabel->Text("Got a click");
    $@ or die "Error in eval: $@";   $$$verify
...and always check for $@ after an eval!

Text Fields

How can I get a vertical scrollbar in a textfield?

Add these options when you create the textfield:
-multiline   => 1
-autovscroll => 1
This should do the trick.

How can I get the selected portion of a textfield?

There is a Selection method that returns the start and end of the selection. Then you just make a substr on the Textfield content:

  ($from, $to) = $Textfield->Selection();
  $var = substr($Textfield->Text, $from, $to-$from);

How can I get the _Change event from a RichEdit control?

"I'd like to share a solution to a problem that has been driving me nuts for a while. I changed a Textfield control to a RichEdit and it would not give me the _Change event. I dug in the GUI.xs and could find nothing wrong. I finally tracked it down to the eventmask being zero, which means that the notification messages don't come to the GUI message loop in the first place. The workaround is to do

  $MainWindow->myRichEditField->SendMessage (0x445, 0, 1);

That sends EM_SETEVENTMASK (0x445) to the control with the ENM_CHANGE bit set. Hope that spares somebody else a headache."

How can I format text in a RichEdit control?

There is a SetCharFormat method to the RichEdit control.

$Rich->Select ($from_here, $to_there);
$Rich->SetCharFormat (-color => $flashy_pink)
To set the font at the beginning you can use:
my $Font = new Win32::GUI::Font(
-name => "Courier New", 
-height => 16,
-bold => 0,

### or the font/style of your choice...
### and then in your AddRichEdit use

-font => $Font


How can I prevent the user from choosing more than one item in a Listview?

You can use the -singlesel option on the ListView to achieve what you want.

How can I display a popup menu within a ListView?

Here is an example how it can be done:

# define popup menu for listview
my $PopupMenu = new Win32::GUI::Menu(
    "Item Properties" => "ItemProp",
    ">&Properties" => "ItemProperties",
# get right-click in listview
sub DataView_RightClick {
   my($X, $Y) = Win32::GUI::GetCursorPos();
   $MainWindow->TrackPopupMenu($PopupMenu->{ItemProp},$X, $Y);
# clicked on particular menu item in popup menu
sub ItemProperties_Click {
   ## code you want to process;


What are the icon, button and modality values for MessageBox?

"I think these will work, I haven't tried them all.

0 - display only the OK button
1 - display OK and Cancel buttons
2 - display Abort, Retry, and Ignore buttons
3 - display Yes, No, and Cancel buttons
4 - display Yes and No buttons
5 - display Retry and Cancel buttons

16 - display Critical Message icon
32 - display Warning Query icon
48 - display Warning Message icon
64 - display Information Message icon

0 - set first button as default
256 - set second button as default
512 - set third button as default
768 - set fourth button as default

Return Values
1 - OK
2 - Cancel
3 - Abort
4 - Retry
5 - Ignore
6 - Yes
7 - No"


How can I change the cursor to an hourglass and back?

Basically, what you want is

Win32::GUI::SetCursor ()
the tricky thing is to get the standard resource of the hourglass. Feel free to use my perl module for exactly this: (Notice: Win32::API must be installed)
Win32::GUI::SetCursor (WinCursor (WAIT)); # hourglass ...
Win32::GUI::SetCursor (WinCursor ()); # ... and back
What this module does is
$LoadImage = new Win32::API ('user32', 'LoadImage', [N,N,I,I,I,I],N)
or die 'can\'t find LoadImage function';
%cursors =
'NORMAL'      => 32512,
'IBEAM'       => 32513,
'WAIT'        => 32514,
sub WinCursor
local $_ = $cursors{$_[0]} or $cursors{'NORMAL'};
return $LoadImage->Call (0, $_, 2, 0, 0, 0x8040);

First download the module and store it under the name '' in the directory where you have your perl program, or in the perl modules directory. Second, make sure Win32::API is installed, or install it using ppm. The perl program below now shows the hourglass cursor for two seconds each time the button "search now" is clicked.

use strict;
use Win32::GUI;

#How to get the "wait cursor" resource.
#Alternative 1, using the Win32::API module:
use Win32::API;
my $loadImage = new Win32::API ('user32', 'LoadImage', ['N','N','I','I','I','I'],'N')
 or die 'cannot find LoadImage function';
my $waitCursor = $loadImage->Call(0, 32514, 2, 0, 0, 0x8040);

#Alternative 2, using the WinStRes module (uses Win32::API)
#use WinStRes;  #download from
#my $waitCursor = WinCursor("WAIT");

my $main = Win32::GUI::Window->new(
  -name    => "Main",
  -title   => "Win32-GUI: Hourglass Cursor Demo",
  -left    => 100,
  -top     => 100,
  -width   => 600,
  -height  => 400,

my $search = $main->AddButton(
  -name    => 'Search',
  -text    => 'search now', 
  -left    => 25,
  -top     => 25,

sub Search_Click {
  print "Searching..."; 
  my $oldCursor = Win32::GUI::SetCursor($waitCursor);  #show hourglass ...
  sleep 2;  #do your search here
  print "done\n";
  Win32::GUI::SetCursor($oldCursor);  #show previous arrow cursor again
  return 1;

sub Main_Terminate {
  print "Main Window terminated\n";
  return -1;


Extensions to Win32::GUI

Is there a spreadsheet (grid) look-a-like solution or component?

"No, but I'm thinking about implementing one (just thinking for now :-). "

Is there a inline webbrowser somewhere ? or a HTML or XML parser?

"No, and I don't think I will try to implement one :-) You should instead look at Win32::OLE, to see if you can embed an InternetExplorer instance in a window. That said, it seems that RichEdit 3.0 (available in Windows 2000) has a lot of nice features, that I'll try to implement if time permits."

So, I used the Win32:OLE example from Learning Perl on Win32:

use Win32::OLE;
my $browser = CreateObject OLE "InternetExplorer.Application.1" || return 0;
$browser->{'Visible'} = 1;
This works fine, except I'm now forcing the user to use IE instead of Netscape. And it's possible (not likely I realize) that they don't even have IE. So what happens then?

To show an URL in the default browser of your PC, the Win32::Shell helps. Win32::Shell can be downloaded from the Activestate archive using ppm. It is not in CPAN at present (June 2001).

use Win32::Shell;
$url = "";
Win32::Shell::Execute("open", $url, undef, undef, "SW_SHOWNORMAL");
This starts the default browser opened to the correct URL, with no delay, and no console window.

Is there support for JPG or common image formats like .PNG or .GIF?

Win32::GUI::DIBitmap add new reading/writing bitmap formats to Win32::GUI and some images manipulations (Conversion, Screen capture, ...).
This package uses FreeImage 2.4.1, an open source image library supporting all common bitmap formats (visit :

Supports many formats, such as:

  Format  Reading Writing Description.
  BMP     Y       Y       Windows or OS/2 Bitmap
  ICO     Y       N       Windows Icon
  JPEG    Y       Y       JPEG - JFIF Compliant
  JNG     Y       N       JPEG Network Graphics
  KOALA   Y       N       C64 Koala Graphics
  IFF     Y       N       IFF Interleaved Bitmap
  MNG     Y       N       Multiple Network Graphics
  PBM     Y       Y       Portable Bitmap (ASCII)
  PBMRAW  Y       Y       Portable Bitmap (RAW)
  PCD     Y       N       Kodak PhotoCD
  PCX     Y       N       Zsoft Paintbrush
  PGM     Y       Y       Portable Greymap (ASCII)
  PGMRAW  Y       Y       Portable Greymap (RAW)
  PNG     Y       Y       Portable Network Graphics
  PPM     Y       Y       Portable Pixelmap (ASCII)
  PPMRAW  Y       Y       Portable Pixelmap (RAW)
  RAS     Y       N       Sun Raster Image
  TARGA   Y       N       Truevision Targa
  TIFF    Y       Y       Tagged Image File Format
  WBMP    Y       Y       Wireless Bitmap
  PSD     Y       N       Adobe Photoshop

Current version : 0.03

DIBitmap : Win32::GUI::DIBitmap Docs (28 ko) : Source Code and samples (You must download FreeImage source code for build it, see Readme.txt) (266 ko) : PPM distribution for Active Perl 5.003 (see Readme) (271 ko) : PPM distribution for Active Perl 5.6 (see Readme)

 For more information see  (email from Laurent Rocher Aug 20, 2001)

How can I deal with moving and resizing stuff when a window is resized?

"Dealing with moving and resizing stuff when a window is resized is really annoying, not to mention boring. So I created a class to make that easier. That was a lot more fun for some reason :) Anyway, the result is Win32::GUI::Resizer.
Please try it out if you like and let me know what you think. "  (email from Johan Lindström, Sourcerer, Boss Casinos Ltd, Antigua,

Is there a Win32-GUI-Builder available (i.e. a visual aid in designing the GUI)?

yes, well.. at least a basic one. Download
For more information, check the Win32::GUI mailing-list, the emails from David Hiltz.

Another one is the GUI Loft by Johan Lindström. This is a powerful and easy-to-use WYSIWYG editor for designing Win32::GUI windows, dialog boxes and toolwindows. It is also a set of classes used to create the window for you at runtime.

Download source and/or binaries here:

The Perl Artistic License applies.

There is an extensive User Manual in the Help menu, please read it. But try the program first, you are programmers and power-users after all, right? :)

Currently supported controls are: Window, DialogBox, ToolbarWindow, Button, Label, TextField, RadioButton, CheckBox, GroupBox, Listbox, RichEdit, ListView, ComboBox, TreeView, TabStrip, Timer, ImageList

Cool features include:

- Pretty extensive WYSIWYG support + 100% accurate preview

- Pretty complete support for Win32::GUI control options--and then some

- It's actually easy to use (IMHO :)

- Docs and demo code

- No-code runtime TabStrip management