Fltk Glut compatability

#include <FL/glut.H>

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

All files calling glut procedures must be compiled with C++. 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. I was unable to get some calls to glu to compile without adding some casts, apparently due to errors in the glu header files.

You must link with -lFl. If you call any glut drawing functions that fltk does not emulate (glutExtensionsSupported(), glutWire*(), glutSolid*(), and glutStroke*()), you will also have to link with -lglut, after -lFl.

Most of glut.H is inline functions. You should take a look at it (and maybe at glut.C 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 3.3 distribution.

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:
- glutLayerGet(GLUT_LAYER_IN_USE)
- glutLayerGet(GLUT_HAS_OVERLAY)
- glutSetColor(), glutGetColor(), glutCopyColormap()
- glutInitDisplayMode(GLUT_STEREO)
- glutInitDisplayMode(GLUT_LUMINANCE)
- glutPushWindow()
- glutWarpPointer()
- Spaceball, buttonbox, dials, tablet functions, glutDeviceGet()
- glutWindowStatusFunc()
- glutGet(GLUT_WINDOW_NUM_CHILDREN)
- glutGet(GLUT_SCREEN_WIDTH_MM)
- glutGet(GLUT_SCREEN_HEIGHT_MM)
- glutGet(GLUT_ELAPSED_TIME)
- glutVideoResize() missing.
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 F12.
The strings passed as menu labels are not copied.
glutPostRedisplay() does not work if called from inside a display function. You must use glutIdleFunc() if you want your display to update continuously.
glutSwapBuffers() does not work from inside a display function. This is on purpose, because fltk swaps the buffers for you.
glutUseLayer() does not work well, and should only be used to initialize transformations inside a resize callback. You should redraw overlays by using glutOverlayDisplayFunc().
Overlays are cleared before the overlay display function is called. glutLayerGet(GLUT_OVERLAY_DAMAGED) always returns true, this fixed some glut overlay programs. You must rewrite your code so that gl_color() is used to choose colors in an overlay, or you will get random overlay colors.
glutSetCursor(GLUT_CURSOR_FULL_CROSSHAIR) just results in a small crosshair.
The fonts used by glutBitmapCharacter() and glutBitmapWidth() may be different.
glutInit(argc,argv) will consume different switches than glut does. It accepts the switches recognized by Fl_Window::arg(), and will accept any abbreviation of these switches (such as -d for -display).

Mixing Glut code 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 show()'ing the window at the point it is created, which means the Fl_Window parent window must already be show()n.

Don't call glutInit().

Create your Fl_Window, and any fltk widgets. Leave a blank area in the window for your glut window.

show() the Fl_Window. Perhaps call show(argc,argv).

Call window->begin() so the glut window will be automatically added to it.

Use glutInitWindowSize() and glutInitWindowPosition() to set the location in the parent window to put the glut window.

Put your glut code next. It probably does not need many changes. Call window->end() immediately after the glutCreateWindow()!

You can call either glutMainLoop() or Fl::run() or loop calling Fl::wait() to run the program.

class Fl_Glut_Window : public Fl_Gl_Window

Each Glut window is an instance of this class, which is a subclass of Fl_Gl_Window. 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 FL's method of creating windows.

The current glut window is available in Fl_Glut_Window *glut_window.

new Fl_Glut_Window(...) is the same as glutCreateWindow() except it does not show() the window or make the window current.

window->make_current() is the same as glutSetWindow(number). If the window has not had show() called on it yet, some functions that assumme a gl context will not work. If you do show() the window, call make_current() again to set the context.

~Fl_Glut_Window() is the same as glutDestroyWindow().

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