/**

 \page  glut    GLUT Compatibility

This appendix describes the GLUT compatibility header file supplied with
FLTK. FLTK's GLUT compatibility is based on the original GLUT 3.7 and
the follow-on FreeGLUT 2.4.0 libraries.

\section glut_using Using the GLUT Compatibility Header File

You should be able to compile existing GLUT source code by including
\c <FL/glut.H> instead of \c <GL/glut.h>.  This can be
done by editing the source, by changing the \c -I switches to
the compiler, or by providing a symbolic link from \c GL/glut.h
to \c FL/glut.H.

<i>All files calling GLUT procedures must be compiled with C++</i>. You
may have to alter them slightly to get them to compile without warnings,
and you may have to rename them to get make to use the C++ compiler.

You must link with the FLTK library. Most of \c FL/glut.H
is inline functions.  You should take a look at it (and maybe at
\c test/glpuzzle.cxx in the FLTK source) if you are having trouble
porting your GLUT program.

This has been tested with most of the demo programs that come with
the GLUT and FreeGLUT distributions.

\section glut_known_problems Known Problems

The following functions and/or arguments to functions are missing,
and you will have to replace them or comment them out for your code
to compile:

\li \p glutGet(GLUT_ELAPSED_TIME)
\li \p glutGet(GLUT_SCREEN_HEIGHT_MM)
\li \p glutGet(GLUT_SCREEN_WIDTH_MM)
\li \p glutGet(GLUT_WINDOW_NUM_CHILDREN)
\li \p glutInitDisplayMode(GLUT_LUMINANCE)
\li \p glutKeyboardUpFunc(void(*callback)(unsigned char key, int x, int y))
\li \p glutLayerGet(GLUT_HAS_OVERLAY)
\li \p glutLayerGet(GLUT_LAYER_IN_USE)
\li \p glutPushWindow()
\li \p glutSetColor(), \p glutGetColor(), \p glutCopyColormap()
\li \p glutVideoResize() missing.
\li \p glutWarpPointer()
\li \p glutWindowStatusFunc()
\li Spaceball, buttonbox, dials, and tablet functions

Most of the symbols/enumerations have different values than GLUT uses.
This will break code that relies on the actual values. The only
symbols guaranteed to have the same values are true/false pairs like
GLUT_DOWN and GLUT_UP, mouse buttons
GLUT_LEFT_BUTTON, GLUT_MIDDLE_BUTTON, GLUT_RIGHT_BUTTON, and
GLUT_KEY_F1 thru GLUT_KEY_F12.

The strings passed as menu labels are not copied.

\p glutPostRedisplay() does not work if called from inside a
display function.  You must use \p glutIdleFunc() if you want
your display to update continuously.

\p glutSwapBuffers() does not work from inside a display
function.  This is on purpose, because FLTK swaps the buffers for you.

\p glutUseLayer() does not work well, and should only be used
to initialize transformations inside a resize callback.  You should
redraw overlays by using \p glutOverlayDisplayFunc().

Overlays are cleared before the overlay display function is called.
\p glutLayerGet(GLUT_OVERLAY_DAMAGED) always returns true for
compatibility with some GLUT overlay programs.  You must rewrite your
code so that \p gl_color() is used to choose colors in an
overlay, or you will get random overlay colors.

\p glutSetCursor(GLUT_CURSOR_FULL_CROSSHAIR) just results in a
small crosshair.

The fonts used by \p glutBitmapCharacter() and \p glutBitmapWidth()
may be different.

\p glutInit(argc,argv) will consume different switches than
GLUT does.  It accepts the switches recognized by
Fl::args(),
and will accept any abbreviation of these
switches (such as "-di" for "-display").

\section glut_mixing Mixing GLUT and FLTK Code

You can make your GLUT window a child of a Fl_Window with the
following scheme.  The biggest trick is that GLUT insists on
a call to \p show() the window at the point it is created, which means the
Fl_Window parent window must already be shown.

\li Don't call \p glutInit().
\li Create your Fl_Window, and any FLTK widgets.  Leave a
    blank area in the window for your GLUT window.
\li \p show() the Fl_Window.  Perhaps call \p show(argc,argv).
\li Call <tt>window->begin()</tt> so that the GLUT window will  be
    automatically added to it.
\li Use \p glutInitWindowSize() and \p glutInitWindowPosition()
    to set the location in the  parent window to put the GLUT window.
\li Put your GLUT code next.  It probably does not need many changes.
    Call <tt>window->end()</tt> immediately after the
    \p glutCreateWindow()!
\li You can call either \p glutMainLoop(), Fl::run(),
    or loop calling Fl::wait() to run  the program.


\section glut_Fl_Glut_Window class Fl_Glut_Window

\subsection glut_class_hierarchy Class Hierarchy

\code
Fl_Gl_Window
   |
   +----Fl_Glut_Window
\endcode

\subsection glut_include_files Include Files

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

\subsection glut_description Description

Each GLUT window is an instance of this class.  You may find it useful
to manipulate instances directly rather than use GLUT window id's.
These may be created without opening the display, and thus can fit
better into FLTK's method of creating windows.

The current GLUT window is available in the global variable
\p glut_window.

<tt>new %Fl_Glut_Window(...)</tt> is the same as
\p glutCreateWindow() except it does not \p show() the window
or make the window current.

<tt>window->make_current()</tt> is the same as \p glutSetWindow(number).
If the window has not had \p show() called on it yet, some functions
that assume an OpenGL context will not work.
If you do \p show() the window, call \p make_current()
again to set the context.

<tt>~Fl_Glut_Window()</tt> is the same as \p glutDestroyWindow().

\subsection glut_members Members

The Fl_Glut_Window class contains several public members that can
be altered directly:

<CENTER><TABLE WIDTH="80%" BORDER="1" ALT="Fl_Glut_Window public members.">
<TR>
        <TH>member</TH>
        <TH>description</TH>
</TR>
<TR>
        <TD>display</TD>
        <TD>A pointer to the function to call to draw the normal planes.</TD>
</TR>
<TR>
        <TD>entry</TD>
        <TD>A pointer to the function to call when the mouse moves into
        or out of the window.</TD>
</TR>
<TR>
        <TD>keyboard</TD>
        <TD>A pointer to the function to call when a regular key is pressed.</TD>
</TR>
<TR>
        <TD>menu[3]</TD>
        <TD>The menu to post when one of the mouse buttons is pressed.</TD>
</TR>
<TR>
        <TD>mouse</TD>
        <TD>A pointer to the function to call when a button is pressed or
        released.</TD>
</TR>
<TR>
        <TD>motion</TD>
        <TD>A pointer to the function to call when the mouse is moved with
        a button down.</TD>
</TR>
<TR>
        <TD>overlaydisplay</TD>
        <TD>A pointer to the function to call to draw the overlay planes.</TD>
</TR>
<TR>
        <TD>passivemotion</TD>
        <TD>A pointer to the function to call when the mouse is moved with
        no buttons down.</TD>
</TR>
<TR>
        <TD>reshape</TD>
        <TD>A pointer to the function to call when the window is resized.</TD>
</TR>
<TR>
        <TD>special</TD>
        <TD>A pointer to the function to call when a special key is pressed.</TD>
</TR>
<TR>
        <TD>visibility</TD>
        <TD>A pointer to the function to call when the window is iconified
        or restored (made visible.)</TD>
</TR>
</TABLE></CENTER>

\subsection glut_methods Methods

Fl_Glut_Window::Fl_Glut_Window(int x, int y, int w, int h, const char *title = 0) <br>
Fl_Glut_Window::Fl_Glut_Window(int w, int h, const char *title = 0)

\par
The first constructor takes 4 int arguments to create the window with
a preset position and size.  The second constructor with 2 arguments
will create the window with a preset size, but the window manager will
choose the position according to its own whims.

virtual Fl_Glut_Window::~Fl_Glut_Window()

\par
Destroys the GLUT window.

void Fl_Glut_Window::make_current()

\par
Switches all drawing functions to the GLUT window.


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