Sanko Robinson > FLTK-0.532009 > FLTK::Window



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FLTK::Window - Where you put stuff

Description ^

This widget produces an actual window. This can either be a main window, with a border and title and all the window management controls, or a "subwindow" inside a window. This is controlled by whether or not the window has a parent(). Internally there are now significant differences between "main" windows and "subwindows" and these really should be different classes, they are the same for historic reasons.

Once you create a window, you usually add children Widgets to it by using add(child) or by using begin() and then constructing the children. See FLTK::Group for more information on how to add and remove children.

There are several subclasses of FLTK::Window that provide double-buffering, overlay, menu, and OpenGL support.

The window's callback is done if the user tries to close a window using the window manager and FLTK::modal() is zero or equal to the window. Window has a default callback that calls hide() and calls exit(0) if this is the last top-level window.

You can set the shortcut() and then that key will call the callback. If you don't change it then that key will close the window.

Synopsis ^

  use FLTK;
  my $win = FLTK::Window->new(100, 100, 500, 800);

Functions ^


$window->border( $set );

If set is a true value, then a window border will be set, otherwise the window will have neither border nor caption.

my $set = $window->border( );


$window->borders( $rect );

$rect is set to the the size of the borders that will be added around this window. This is done by querying the window system. Because it is more convienent for most code the result is actually the rectangle that would be around the border if this window was zero in size and placed at 0,0. x,y are typically negative and w,h are typically positive. To get the actual rectangle around your window, add these values to the window's size.


$window->child_of( $parent );

Tell the system that this window will not have an icon, it will dissappear and reappear when parent is iconized or shown, and it is forced to always be above parent. On X this is called a "Transient window", and Windows calls this a "overlapping child". parent is different than the parent(), which must be zero.

Changing this value causes DESTROY() to be called, due to stupid limitations in X and Windows.

Win32 and some X window managers have an annoying bug where calling show() on this will also raise the parent window to right below this, making many useful user interface designs impossible!

If you want a dialog that blocks interaction with the other windows of your application or with all other applications, you need to look at exec() (or possibly FLTK::modal()).


$window->clear_double_border( );

Turn off double buffering, so that drawing directly goes to the visible image on the screen. Not all systems can do this, they will remain double buffered even if this is off.


my $style = $window->default_style( );

By default a window has box() set to FLAT_BOX, and the color() set to GRAY75, which is a special color cell that is altered by FLTK::set_background().

If you plan to turn the border() off you may want to change the box() to UP_BOX. You can also produce something that looks like an arbitrary shape (though really it is showing the original screen contents in the "outside" area, so the window had better be temporary and the user cannot move it) by setting the box() to NO_BOX and making draw() only draw the opaque part.

$window->default_style( $style );

Set the style.


my $db_set = $window->double_buffer( );

Returns a true value if set_double_buffer() was called, returns a false value if clear_double_buffer() was called. If neither has been called, this returns a machine-dependant state (systems where double buffering is efficient turn it on by default).


my $window = $window->drawing_window( );

Returns the Window currently being drawn into. To set this use make_current(). It will already be set when draw() is called.


$window->erase_overlay( );

Indicate that the overlay drawn with draw_overlay() is blank. draw_overlay() will not be called until redraw_overlay() is called again.


my $return = $window->exec( $parent, $grab );

The window is popped up and this function does not return until make_exec_return() is called, or the window is destroyed or hide() is called, or FLTK::exit_modal() is called. During this time events to other windows in this application are either thrown away or redirected to this window.

This does child_of(parent) (using first() if parent is undefined), so this window is a floating panel that is kept above the parent. It then uses FLTK::modal(this,grab) to make all events go to this window.

The return value is the argument to make_exec_return(), or a false value if any other method is used to exit the loop.

If parent is undefined, the window that last received an event is used as the parent. This is convenient for popups that appear in response to a mouse or key click.

See FLTK::modal() for what grab does. This is useful for popup menus.


my $win = FLTK::first( );

Returns the id of some visible() window. If there is more than one, the last one to receive an event is returned. This is useful as a default value for FLTK::Window::child_of(). FLTK::Window::exec() uses it for this if no other parent is specified. This is also used by FLTK::run() to see if any windows still exist.

FLTK::first( $window );

If this window is visible, this removes it from wherever it is in the list and inserts it at the top, as though it received an event. This can be used to change the parent of dialog boxes run by FLTK::Window::exec() or FLTK::ask().


$window->free_backbuffer( );

Get rid of extra storage created by drawing when double_buffer() was turned on.


$window->fullscreen( $monitor );

Make the window completely fill the monitor, without any window manager border or taskbar or anything else visible. Use fullscreen_off() to undo this.

Known bugs:

  • Older versions of both Linux and Windows will refuse to hide the taskbar. Proposed solutions for this tend to have detrimental effects, such as making it impossible to switch tasks or to put another window atop this one. It appears that newer versions of both Linux and Windows work correctly, so we will not fix this.
  • Many older X window managers will refuse to position the window correctly and instead place them so the top-left of the border in the screen corner. You may be able to fix this by calling hide() first, then fullscreen(), then show(). We don't do this because it causes newer window systems to blink unnecessarily.
  • Some X window managers will raise the window when you change the size.
  • Calling resize() before calling fullscreen_off() will result in unpredictable effects, and should be avoided.
$window->fullscreen( );

Chooses the Monitor that the center of the window is on to be the one to resize to.


$window->fullscreen_off( $x, $y, $w, $h );

Turns off any side effects of fullscreen(), then does resize($x,$y,$w,$h).


$window->hotspot( $widget, $offscreen );

position() the window so that the mouse is pointing at the center of the widget, which may be the window itself. If offscreen is a true value, the window is allowed to extend off the Monitor (some X window managers do not allow this).

$window->hotspot( $CX, $CY, $offscreen );

position() the window so that the mouse is pointing at the cx,cy position. If offscreen is a true value, the window is allowed to extend off the Monitor (some X window managers do not allow this.


$window->icon( $path );

This loads an icon (.ico) in the window.


my $is_it = $window->iconic( );

Returns a true value if the window is currently displayed as an icon. Returns a false value if the window is not shown() or hide() has been called.

On X this will return true in the time between when show() is called and when the window manager finally puts the window on the screen and causes an expose event.

Returns true if the window is shown but is iconized.


$window->iconize( );

Iconifies the window. If you call this when shown() is false it will show() it as an icon. If the window is already iconified this does nothing.

Call show() to restore the window.

Currently there are only X and Win32 system-specific ways to control what is drawn in the icon. You should not rely on window managers displaying the icons.


$window->iconlabel( $iname );

Sets the text displayed below the icon (or in the taskbar). If you don't set this it defaults to the label() but if that appears to be a filename, it defaults to the last portion after the last / character.


my $label = $window->iconlable( );


$window->label( $name, $iname );

Sets both the label() and the iconlabel().

$window->label( $name );

Sets the window title, which is drawn in the titlebar by the system.

my $title = $window->label( );

Returns the window title.


$window->make_exec_return( $return_value );

If exec() is currently being called, make it hide this window and return return_value.

Does nothing if exec() is not being called.

Results are undefined if the innermost exec() is being called on a window other than this one. Current behavior is to cause that exec to return false.


my $win = $window->new( $x, $y, $w, $h, $label );

Creates a new FLTK::Window object.

my $win = $window->new( $w, $h, $label );

Same but window is placed by OS.


my $win = $window->next( );

Returns the next visible() top-level window, returns undef after the last one. You can use this and first() to iterate through all the visible windows.


$window->redraw_overlay( );

Indicate that the image made by draw_overlay() has changed and must be drawn or redrawn. If the image is blank you should call erase_overlay().

This does nothing if the window is not shown(), it is assummed that overlays are only drawn in response to user input.


$window->resize( $x, $y, $w, $h );

Change the size and position of the window. If shown() is true, these changes are communicated to the window server (which may refuse that size and cause a further resize). If shown() is false, the size and position are used when show() is called. See FLTK::Group for the effect of resizing on the child widgets.

The special value FLTK::USEDEFAULT may be used for X and Y indicate that the system should choose the window's position. This will only work before show() is called.


$window->set_double_buffer( );

If the window is double-buffered, all drawing is done first to some offscreen image, and then copied to the screen as a single block. This eliminates blinking as the window is updated, and often the application looks faster, even if it actually is slower.


$window->show( $parent );

Same as child_of(parent); show().

$window->show( $argc, @argv );

This must be called after FLTK::args($argc,@argv) to show the "main" window, this indicates which window should be affected by any -geometry switches. In addition if FLTK::args() has not been called yet this does so, this is a useful shortcut for the main window in a small program.

$window->show( );

Cause the window to become visible. It is harmless to call this multiple times.

For subwindows (with a parent()) this just causes the window to appear. Currently no guarantee about stacking order is made.

For a outer window (one with no parent()) this causes the window to appear on the screen, be de-iconized, and be raised to the top. Depending on child_of() settings of this window and of windows pointing to it, and on system and window manager settings, this may cause other windows to also be deiconized and raised, or if this window is a child_of() then this window may remain iconized.

Window::show() is not a virtual override of Widget::show(). You can call either one. The only difference is that if an outer window has had show() called already, Window::show() will raise and deiconize it, while Widget::show() will only un-hide() it, making it appear in the same stacking order as before but not changing the iconization state (on some X window managers it will deiconize anyway).

The first time this is called is when the actual "system" window (ie the X window) is created. Before that an fltk window is simply an internal data structure and is not visible outside your program. To return to the non-system-window state call DESTROY(). hide() will "unmap" the system window.

The first time show() is called on any window is when fltk will call FLTK::open_display() and FLTK::load_theme(), unless you have already called them. This allows these expensive operations to be deferred as long as possible, and allows fltk programs to be written that will run without an X server as long as they don't actually show a window.


$window->show_inside( $parent );

Make the window with a normal system border and behavior, but place it inside the parent as though that was the desktop. This is what Windows calls "MDI". Typically the other window (which must already be shown) is a child window so that space can remain around it for a menu/tool bar.

Notice that parent() of the window must be zero and it will remain zero after this is called. Fltk uses a zero parent to indicate that the system is managing the window.

On systems that don't support nested desktops (i.e. X) this does child_of(parent) and show(), which produces an overlapping window that will remain above the frame window.


my $was_it = $window->shown( );

Returns non-zero if show() has been called, but DESTROY() has not been called. Note that this returns true if hide() was called or if the user has iconized the window.


$window->size_range( $minW, $minH, $maxW, $maxH, $dw, $dh );

Set the allowable range the user can resize this window to. This only works for top-level windows.

$minW and $minH are the smallest the window can be.
$maxW and $maxH are the largest the window can be. If either is equal to the minimum then you cannot resize in that direction. If either is zero then FLTK picks a maximum size in that direction such that the window will fill the screen.
$dw and $dh are size increments. The window will be constrained to widths of $minW + N * $dw, where N is any non-negative integer. If these are less or equal to 1 they are ignored. (this is ignored on WIN32)

It is undefined what happens if the current size does not fit in the constraints passed to size_range().

If this function is not called, FLTK tries to figure out the range from the setting of resizeable():

If resizeable() is undefined (this is the default), then the window cannot be resized.
If either dimension of resizeable() is less than 100, then that is considered the minimum size. Otherwise the resizeable() has a minimum size of 100.
If either dimension of resizeable() is zero, then that is also the maximum size (so the window cannot resize in that direction).


$window->system_layout( );

Resizes the actual system window to match the current size of the fltk widget. You should call this in your layout() method if xywh have changed. The layout_damage() flags must be on or it won't work.

Author ^

Sanko Robinson <> -

License and Legal ^

Copyright (C) 2008-2010 by Sanko Robinson <>

This program is free software; you can redistribute it and/or modify it under the terms of The Artistic License 2.0. See the LICENSE file included with this distribution or notes on the Artistic License 2.0 for clarification.

When separated from the distribution, all original POD documentation is covered by the Creative Commons Attribution-Share Alike 3.0 License. See the clarification of the CCA-SA3.0.

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