/**

 \page	osissues	Operating System Issues

This appendix describes the operating system specific interfaces in FLTK:
\li \ref osissues_accessing
\li \ref osissues_unix
\li \ref osissues_win32
\li \ref osissues_macos

\section osissues_accessing Accessing the OS Interfaces

All programs that need to access the operating system
specific interfaces must include the following header file:

\code
#include <FL/x.H>
\endcode

Despite the name, this header file will define the
appropriate interface for your environment. The pages that
follow describe the functionality that is provided for each
operating system.

<CENTER>
<TABLE WIDTH="90%" BORDER="1" CELLPADDING="5" CELLSPACING="0" BGCOLOR="#cccccc">
<TR>
	<TD><B>WARNING:</B>

	The interfaces provided by this header file may
	change radically in new FLTK releases. Use them only
	when an existing generic FLTK interface is not
	sufficient.

	</TD>
</TR>
</TABLE>
</CENTER>

\section osissues_unix The UNIX (X11) Interface

The UNIX interface provides access to the X Window System
state information and data structures.

\subsection osissues_x_events Handling Other X Events

void Fl::add_handler(int (*f)(int))

\par
Installs a function to parse unrecognized events. If FLTK
cannot figure out what to do with an event, it calls each of
these functions (most recent first) until one of them returns
non-zero. If none of them returns non-zero then the event is
ignored.

\par
FLTK calls this for any X events it does not recognize, or X
events with a window ID that FLTK does not recognize. You can
look at the X event in the \c fl_xevent variable.

\par
The argument is the FLTK event type that was not handled, or
zero for unrecognized X events. These handlers are also called
for global shortcuts and some other events that the widget they
were passed to did not handle, for example
\c FL_SHORTCUT.

extern XEvent *fl_xevent

\par
This variable contains the most recent X event.

extern ulong fl_event_time

\par
This variable contains the time stamp from the most recent X
event that reported it; not all events do. Many X calls like cut
and paste need this value.

Window fl_xid(const Fl_Window *)

\par
Returns the XID for a window, or zero if not \c shown().

Fl_Window *fl_find(ulong xid)

\par
Returns the Fl_Window that corresponds to the given
XID, or \c NULL if not found. This function uses a cache
so it is slightly faster than iterating through the windows
yourself.

int fl_handle(const XEvent &)

\par
This call allows you to supply the X events to FLTK, which
may allow FLTK to cooperate with another toolkit or library. The
return value is non-zero if FLTK understood the event. If the
window does not belong to FLTK and the \c add_handler()
functions all return 0, this function will return false.

\par
Besides feeding events your code should call Fl::flush()
periodically so that FLTK redraws its windows.

\par
This function will call the callback functions. It will not
return until they complete. In particular, if a callback pops up
a modal window by calling
fl_ask(),
for instance, it will not return until the modal function
returns.

\subsection osissues_drawing_xlib Drawing using Xlib

The following global variables are set before
Fl_Widget::draw() is called, or by Fl_Window::make_current():

\code
extern Display *fl_display;
extern Window fl_window;
extern GC fl_gc;
extern int fl_screen;
extern XVisualInfo *fl_visual;
extern Colormap fl_colormap;
\endcode

You must use them to produce Xlib calls.  Don't attempt to change
them. A typical X drawing call is written like this:

\code
XDrawSomething(fl_display, fl_window, fl_gc, ...);
\endcode

Other information such as the position or size of the X
window can be found by looking at Fl_Window::current(),
which returns a pointer to the Fl_Window being drawn.

unsigned long fl_xpixel(Fl_Color i) <br>
unsigned long fl_xpixel(uchar r, uchar g, uchar b)

\par
Returns the X pixel number used to draw the given FLTK color
index or RGB color. This is the X pixel that
\ref drawing_colors "fl_color()"
would use.

int fl_parse_color(const char* p, uchar& r, uchar& g, uchar& b)

\par
Convert a name into the red, green, and blue values of a color
by parsing the X11 color names. On other systems, \c fl_parse_color()
can only convert names in hexadecimal encoding, for example <tt>\#ff8083</tt>.
 
extern XFontStruct *fl_xfont

\par
Points to the font selected by the most recent
\ref ssect_Fonts "fl_font()".
This is not necessarily the current font of \c fl_gc,
which is not set until
\ref ssect_Text "fl_draw()"
is called. If FLTK was compiled with Xft support, \c fl_xfont
will usually be 0 and \c fl_xftfont will contain a pointer 
to the \c XftFont structure instead.

extern void *fl_xftfont

\par
If FLTK was compiled with Xft support enabled, \c fl_xftfont
points to the xft font selected by the most recent
\ref ssect_Fonts "fl_font()".
Otherwise it will be 0. \c fl_xftfont should be cast to 
<tt>XftFont*</tt>.

\subsection osissues_xvisual Changing the Display, Screen, or X Visual

FLTK uses only a single display, screen, X visual, and X
colormap. This greatly simplifies its internal structure and
makes it much smaller and faster. You can change which it uses
by setting global variables
<I>
before the first Fl_Window::show() is called.
</I>
You may also want to call Fl::visual(), which is a portable interface
to get a full color and/or double buffered visual.

int Fl::display(const char *)

\par
Set which X display to use.  This actually does
<tt>putenv("DISPLAY=...")</tt> so that child programs
will display on the same screen if called with \c exec().
This must be done before the display is opened. This call is
provided under MacOS and WIN32 but it has no effect.

extern Display *fl_display

\par
The open X display. This is needed as an argument to most
Xlib calls. Don't attempt to change it! This is \c NULL
before the display is opened.

void fl_open_display()

\par
Opens the display. Does nothing if it is already open. This
will make sure \c fl_display is non-zero. You should call
this if you wish to do X calls and there is a chance that your
code will be called before the first \c show() of a window.

\par
This may call Fl::abort() if there is an error opening the display.

void fl_close_display()

\par
This closes the X connection. You do \e not need to call
this to exit, and in fact it is faster to not do so! It may be
useful to call this if you want your program to continue without
the X connection. You cannot open the display again, and
probably cannot call any FLTK functions.

extern int fl_screen

\par
Which screen number to use. This is set by
\c fl_open_display() to the default screen. You can change
it by setting this to a different value immediately afterwards.
It can also be set by changing the last number in the
Fl::display() string to "host:0.#".

extern XVisualInfo *fl_visual <br>
extern Colormap fl_colormap

\par
The visual and colormap that FLTK will use for all windows.
These are set by \c fl_open_display() to the default
visual and colormap. You can change them before calling
\c show() on the first window. Typical code for changing
the default visual is:
\code
Fl::args(argc, argv); // do this first so $DISPLAY is set
fl_open_display();
fl_visual = find_a_good_visual(fl_display, fl_screen);
if (!fl_visual) Fl::abort("No good visual");
fl_colormap = make_a_colormap(fl_display, fl_visual->visual, fl_visual->depth);
// it is now ok to show() windows:
window->show(argc, argv);
\endcode

\subsection osissues_specialx Using a Subclass of Fl_Window for Special X Stuff

FLTK can manage an X window on a different screen, visual
and/or colormap, you just can't use FLTK's drawing routines to
draw into it. But you can write your own \c draw() method
that uses Xlib (and/or OpenGL) calls only.

FLTK can also manage XID's provided by other libraries or
programs, and call those libraries when the window needs to be
redrawn.

To do this, you need to make a subclass of
Fl_Window
and override some of these virtual functions:

virtual void Fl_Window::show()

\par
If the window is already \c shown() this must cause it
to be raised, this can usually be done by calling Fl_Window::show().
If not \c shown() your implementation must call either
Fl_X::set_xid() or Fl_X::make_xid().

\par
An example:
\code
void MyWindow::show() {
  if (shown()) {Fl_Window::show(); return;}  // you must do this!
  fl_open_display();	// necessary if this is first window
  // we only calculate the necessary visual colormap once:
  static XVisualInfo *visual;
  static Colormap colormap;
  if (!visual) {
    visual = figure_out_visual();
    colormap = XCreateColormap(fl_display, RootWindow(fl_display,fl_screen),
                               vis->visual, AllocNone);
  }
  Fl_X::make_xid(this, visual, colormap);
}
\endcode

\verbatim
Fl_X *Fl_X::set_xid(Fl_Window*, Window xid)
\endverbatim

\par
Allocate a hidden class called an Fl_X, put the
XID into it, and set a pointer to it from the Fl_Window.
This causes Fl_Window::shown() to return true.

void Fl_X::make_xid(Fl_Window*, XVisualInfo* = fl_visual, Colormap = fl_colormap)

\par
This static method does the most onerous parts of creating an
X window, including setting the label, resize limitations, etc.
It then does Fl_X::set_xid() with this new window and maps the window.

virtual void Fl_Window::flush()

\par
This virtual function is called by Fl::flush() to
update the window. For FLTK's own windows it does this by
setting the global variables \c fl_window and \c fl_gc
and then calling the \c draw() method.  For
your own windows you might just want to put all the drawing code
in here.

\par
The X region that is a combination of all \c damage()
calls done so far is in <tt>Fl_X::i(this)->region</tt>. If
\c NULL then you should redraw the entire window. The
undocumented function \c fl_clip_region(XRegion) will
initialize the FLTK clip stack with a region or \c NULL
for no clipping. You must set region to \c NULL afterwards
as \c fl_clip_region() will own and delete it when
done.

\par
If <tt>damage() & FL_DAMAGE_EXPOSE</tt> then only X
expose events have happened. This may be useful if you have an
undamaged image (such as a backing buffer) around.

\par
Here is a sample where an undamaged image is kept somewhere:
\code
void MyWindow::flush() {
  fl_clip_region(Fl_X::i(this)->region);
  Fl_X::i(this)->region = 0;
  if (damage() != 2) {... draw things into backing store ...}
  ... copy backing store to window ...
}
\endcode

virtual void Fl_Window::hide()

\par
Destroy the window server copy of the window. Usually you
will destroy contexts, pixmaps, or other resources used by the
window, and then call Fl_Window::hide() to get rid of
the main window identified by \c xid(). If you override
this, you must also override the destructor as shown:
\code
void MyWindow::hide() {
  if (mypixmap) {
    XFreePixmap(fl_display,mypixmap);
    mypixmap = 0;
  }
  Fl_Window::hide(); // you must call this
}
\endcode

virtual void Fl_Window::~Fl_Window()

\par
Because of the way C++ works, if you override \c hide()
you \e must override the destructor as well (otherwise only
the base class \c hide() is called):
\code
MyWindow::~MyWindow() {
  hide();
}
\endcode

\note Access to the Fl_X hidden class requires to \#define FL_INTERNALS
before compilation.

\subsection osissues_x_icon Setting the Icon of a Window

FLTK currently supports setting a window's icon \b before it
is shown using the Fl_Window::icon() method.

void Fl_Window::icon(const void *)

\par
Sets the icon for the window to the passed pointer. You will
need to cast the icon \c Pixmap to a \c char* when
calling this method. To set a monochrome icon using a bitmap compiled
with your application use:
\code
#include "icon.xbm"

fl_open_display(); // needed if display has not been previously opened

Pixmap p = XCreateBitmapFromData(fl_display, DefaultRootWindow(fl_display),
                                 icon_bits, icon_width, icon_height);

window->icon((const void*)p);
\endcode

\par
To use a multi-colored icon, the XPM format and library
should be used as follows:
\code
#include <X11/xpm.h>
#include "icon.xpm"

fl_open_display();                // needed if display has not been previously opened

Pixmap p, mask;

XpmCreatePixmapFromData(fl_display, DefaultRootWindow(fl_display),
                                 icon_xpm, &p, &mask, NULL);

window->icon((const void *)p);
\endcode

\par
When using the Xpm library, be sure to include it in the list
of libraries that are used to link the application (usually "-lXpm").

<CENTER>
<TABLE WIDTH="90%" BORDER="1" CELLPADDING="5" CELLSPACING="0" BGCOLOR="#cccccc">
<TR>
	<TD><B>NOTE:</B>
	
	You must call Fl_Window::show(int argc, char** argv)
	for the icon to be used. The Fl_Window::show() method
	does not bind the icon to the window.

	</TD>
</TR>
</TABLE>
</CENTER>

\subsection osissues_xresources X Resources

When the
Fl_Window::show(int argc, char** argv)
method is called, FLTK looks for the following X resources:

\li \c background - The default background color
	for widgets (color).

\li \c dndTextOps - The default setting for
	drag and drop text operations (boolean).

\li \c foreground - The default foreground (label)
	color for widgets (color).

\li \c scheme - The default scheme to use (string).

\li \c selectBackground - The default selection
	color for menus, etc. (color).

\li <tt>Text.background</tt> - The default background
	color for text fields (color).

\li \c tooltips - The default setting for
	tooltips (boolean).

\li \c visibleFocus - The default setting for
	visible keyboard focus on non-text widgets (boolean).

Resources associated with the first window's Fl_Window::xclass()
string are queried first, or if no class has been specified then
the class "fltk" is used (e.g. <tt>fltk.background</tt>). If no
match is found, a global search is done (e.g.
<tt>*background</tt>).

\section osissues_win32 The Windows (WIN32) Interface

The Windows interface provides access to the WIN32 GDI
state information and data structures.

\subsection osissues_win32_messages Handling Other WIN32 Messages

By default a single WNDCLASSEX called "FLTK" is
created. All Fl_Window 's are of this class unless you
use Fl_Window::xclass(). The window class is created
the first time Fl_Window::show() is called.

You can probably combine FLTK with other libraries that make
their own WIN32 window classes. The easiest way is to call
Fl::wait(), as it will call \c DispatchMessage()
for all messages to the other windows. If necessary you can let
the other library take over as long as it calls
\c DispatchMessage(), but you will have to arrange for the
function Fl::flush() to be called regularly so that
widgets are updated, timeouts are handled, and the idle
functions are called.

extern MSG fl_msg

\par
This variable contains the most recent message read by
\c GetMessage(), which is called by Fl::wait().
This may not be the
most recent message sent to an FLTK window, because silly WIN32
calls the handle procedures directly for some events (sigh).

void Fl::add_handler(int (*f)(int))

\par
Installs a function to parse unrecognized messages sent to
FLTK windows. If FLTK cannot figure out what to do with a
message, it calls each of these functions (most recent first)
until one of them returns non-zero. The argument passed to the
functions is the FLTK event that was not handled or zero for
unknown messages. If all the handlers return zero then FLTK
calls \c DefWindowProc().

HWND fl_xid(const Fl_Window *)

\par
Returns the window handle for a Fl_Window, or zero
if not \c shown().

Fl_Window *fl_find(HWND xid)

\par
Returns the Fl_Window that corresponds to the given
window handle, or \c NULL if not found. This function uses
a cache so it is slightly faster than iterating through the
windows yourself.

\subsection osissues_win32_gdi Drawing Things Using the WIN32 GDI

When the virtual function Fl_Widget::draw() is
called, FLTK stores all the extra arguments you need to
make a proper GDI call in some global variables:

\code
extern HINSTANCE fl_display;
extern HWND fl_window;
extern HDC fl_gc;
COLORREF fl_RGB();
HPEN fl_pen();
HBRUSH fl_brush();
\endcode

These global variables are set before Fl_Widget::draw() is called, or by
Fl_Window::make_current().
You can refer to them when needed to produce GDI calls, but don't
attempt to change them. The functions return GDI objects for
the current color set by
\ref drawing_colors "fl_color()"
and are created as
needed and cached. A typical GDI drawing call is written like
this:

\code
DrawSomething(fl_gc, ..., fl_brush());
\endcode

It may also be useful to refer to Fl_Window::current()
to get the window's size or position.

\subsection osissues_icon_windows Setting the Icon of a Window

FLTK currently supports setting a window's icon *before* it
is shown using the Fl_Window::icon() method.

void Fl_Window::icon(const void *)

\par
Sets the icon for the window to the passed pointer. You will
need to cast the \c HICON handle to a \c char* when
calling this method. To set the icon using an icon resource
compiled with your application use:
\code
window->icon((const void *)LoadIcon(fl_display, MAKEINTRESOURCE(IDI_ICON)));
\endcode

\par
You can also use the \c LoadImage() and related
functions to load specific resolutions or create the icon from
bitmap data.

<CENTER>
<TABLE WIDTH="90%" BORDER="1" CELLPADDING="5" CELLSPACING="0" BGCOLOR="#cccccc">
<TR>
	<TD><B>NOTE:</B>
	
	You must call Fl_Window::show(int argc, char** argv)
	for the icon to be used. The Fl_Window::show() method
	does not bind the icon to the window.

	</TD>
</TR>
</TABLE>
</CENTER>

\subsection osissues_msdos_console How to Not Get a MSDOS Console Window

WIN32 has a really stupid mode switch stored in the
executables that controls whether or not to make a console
window.

To always get a console window you simply create a console
application (the "/SUBSYSTEM:CONSOLE" option for the
linker). For a GUI-only application create a WIN32 application
(the "/SUBSYSTEM:WINDOWS" option for the linker).

FLTK includes a \c WinMain() function that calls the
ANSI standard \c main() entry point for you.
<I>
This function creates a console window when you use the debug
version of the library.
</I>

WIN32 applications without a console cannot write to
\c stdout or \c stderr, even if they are run from a
console window. Any output is silently thrown away.
Additionally, WIN32 applications are run in the background by
the console, although you can use "start /wait program" to run
them in the foreground.

\subsection osissues_win32_problems Known WIN32 Bugs and Problems

The following is a list of known bugs and problems in the WIN32
version of FLTK:

\li	If a program is deactivated, <tt>Fl::wait()</tt>
	does not return until it is activated again, even though
	many events are delivered to the program. This can cause
	idle background processes to stop unexpectedly. This
	also happens while the user is dragging or resizing
	windows or otherwise holding the mouse down. We were
	forced to remove most of the efficiency FLTK uses for
	redrawing in order to get windows to update while being
	moved. This is a design error in WIN32 and probably
	impossible to get around.

\li	<tt>Fl_Gl_Window::can_do_overlay()</tt> returns true
	until the first time it attempts to draw an overlay, and
	then correctly returns whether or not there is overlay
	hardware.

\li	<tt>SetCapture</tt> (used by <tt>Fl::grab()</tt>)
	doesn't work, and the main window title bar turns gray
	while menus are popped up.

\li	Compilation with <tt>gcc 3.4.4</tt> and <tt>-Os</tt> exposes an
	optimisation bug in gcc. The symptom is that when drawing
	filled circles only the perimeter is drawn. This can for instance
	be seen in the symbols demo. Other optimisation options such
	as -O2 and -O3 seem to work OK. More details can be found
	in STR#1656

\section osissues_macos The Apple OS X Interface

FLTK supports Apple OS X using the Apple Cocoa library. Older
versions of MacOS are no longer supported.

Control, Option, and Command Modifier Keys

\par
FLTK maps the Mac 'control' key to \c FL_CTRL, the
'option' key to \c FL_ALT and the 'Apple' key to
\c FL_META. Furthermore, \c FL_COMMAND designates the 'Apple' key on Mac OS X
and the 'control' key on other platforms.
Keyboard events return the key name in
Fl::event_key() and the keystroke translation in
Fl::event_text(). For example, typing Option-Y on a Mac
US keyboard will set \c FL_ALT in Fl::event_state(),
set Fl::event_key() to 'y' and return the Yen symbol in
Fl::event_text().

Apple "Quit" Event

\par
When the user presses Cmd-Q or requests a termination of the
application, OS X will send a "Quit" Apple Event. FLTK handles
this event by sending an \c FL_CLOSE event to all open
windows. If all windows close, the application will terminate.

Apple "Open" Event

\par
Whenever the user drops a file onto an application icon, OS X
generates an Apple Event of the type "Open". You can have FLTK
notify you of an Open event by calling the \ref fl_open_callback 
function.

void fl_open_display()

\par
Opens the display. Does nothing if it is already open. You should call
this if you wish to do Cocoa or Quartz calls and there is a chance that your
code will be called before the first \c show() of a window.

Window fl_xid(const Fl_Window *)

\par
Returns the window reference for an Fl_Window, or
\c NULL if the window has not been shown. This reference is a pointer
to an instance of the subclass FLWindow of Cocoa's NSWindow class.

Fl_Window *fl_find(Window xid)

\par
Returns the Fl_Window that corresponds to the given window reference,
or \c NULL if not found. FLTK windows that are children of top-level
windows share the \c Window of the top-level window.

void fl_mac_set_about( Fl_Callback *cb, void *user_data, int shortcut) 

\par
Attaches the callback \c cb to the "About myprog" item of the system application menu.
\c cb will be called with NULL first argument and \c user_data second argument.

Fl_Mac_App_Menu class
\par 
The Fl_Mac_App_Menu class allows to localize the application menu.

Fl_Sys_Menu_Bar class

\par
The Fl_Sys_Menu_Bar class allows to build menu bars that, on Mac OS X, are
placed in the system menu bar (at top-left of display), and, on other platforms,
at a user-chosen location of a user-chosen window.

\subsection osissues_quartz Drawing Things Using Quartz

All code inside Fl_Widget::draw()
is expected to call Quartz drawing functions. The Quartz coordinate system 
is flipped to match
FLTK's coordinate system. The origin for all drawing is in the top
left corner of the enclosing Fl_Window. The global variable
\c fl_gc is the appropriate Quartz 2D drawing environment.
Include FL/x.H to declare the \c fl_gc variable.

Fl_Double_Window

OS X double-buffers all windows automatically. On OS X,
Fl_Window and Fl_Double_Window are handled
internally in the same way.

\subsection osissues_mac_files Mac File System Specifics

\par Resource Forks

FLTK does not access the resource fork of an application.
However, a minimal resource fork must be created for OS X
applications. Starting with OS X 10.6, resource forks are
no longer needed.

<CENTER>
<TABLE WIDTH="80%" BORDER="1" BGCOLOR="#cccccc" CELLPADDING="5">
<TR><TD><B>Caution (OS X 10.2 and older):</B>

When using UNIX commands to copy or move executables, OS X
will NOT copy any resource forks! For copying and moving use
CpMac and MvMac respectively. For creating a tar archive, all
executables need to be stripped from their Resource Fork before
packing, e.g. "DeRez fluid > fluid.r". After unpacking the
Resource Fork needs to be reattached, e.g. "Rez fluid.r -o
fluid".
</TD></TR></TABLE>
</CENTER>

It is advisable to use the Finder for moving and copying and
Mac archiving tools like Sit for distribution as they will
handle the Resource Fork correctly. 

\par Mac File Paths

FLTK uses UTF-8-encoded UNIX-style filenames and paths.

\sa  group_macosx 


\htmlonly
<hr>
<table summary="navigation bar" width="100%" border="0">
<tr>
  <td width="45%" align="LEFT">
    <a class="el" href="forms.html">
    [Prev]
    Forms Compatibility
    </a>
  </td>
  <td width="10%" align="CENTER">
    <a class="el" href="index.html">[Index]</a>
  </td>
  <td width="45%" align="RIGHT">
    <a class="el" href="migration_1_1.html">
    Migrating Code from FLTK 1.0 to 1.1
    [Next]
    </a>
  </td>
</tr>
</table>
\endhtmlonly

*/
