Download Freeglut

freeglut is a free-software/open-source alternative to the OpenGL UtilityToolkit (GLUT) library. GLUT was originally written by Mark Kilgard to supportthe sample programs in the second edition OpenGL 'RedBook'. Since then, GLUT hasbeen used in a wide variety of practical applications because it is simple,widely available and highly portable.

GLUT (and hence freeglut) takes care of all the system-specific choresrequired for creating windows, initializing OpenGL contexts, and handling inputevents, to allow for trully portable OpenGL programs.

Download Freeglut

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Pawel started freeglut development on December 1st, 1999. The project is nowvirtually a 100% replacement for the original GLUT with only a few departures(such as the abandonment of SGI-specific features such as the Dials&Buttonsbox and Dynamic Video Resolution) and a shrinking set of bugs.

freeglut adds some additional features over the basic GLUT functionality,such as a larger set of predefined objects to use, the ability to run singleiterations of the event loop, or exit from it gracefully, mousewheel inputcallbacks, optional OpenGL core/compatibility profile context creation,multitouch/multi-pointer input, and support for a larger and growing set ofplatforms, being just some of them.

The freeglut source code repositoryis now hosted on github. So you can also send us pull requests or report bugsthrough the github issues system if you prefer. However lengthy discussionon potential design issues for large contributions are best suited to the mailing list.

The freeglut project does not distribute pre-compiled or otherwise system-specific packages for freeglut.We only release and support freeglut in source code form as listed above.However, most free software package distributionsinclude some version of freeglut, which might provide a more convenient way toobtain and use freeglut. Here's a necessarily woefully incomplete list of suchpackaging efforts for your system:

In December 1999, Mr. Pawel Olzsta started work on an open-source clone of theGLUT library.This open-source clone, which does not use any of the GLUT source code, hasevolved into the present freeglut library. This documentationspecifies the application program interface to the freeglut library.

In developing the freeglut library, we have taken careful stepsto ensure consistency in function operation across the board, in such amanner as to maintain compatibility with GLUT's behavior wheneverpossible. In this section some of the important conventions of freeglut,and their compatibility with GLUT, are made explicit.

There is considerable confusion about the "right thing to do" concerningwindow size and position. GLUT itself is not consistent betweenWindows and UNIX/X11; since platform independence is a virtue forfreeglut, we decided to break with GLUT's behaviour.

Under UNIX/X11, it is apparently not possible to get the window bordersizes in order to subtract them off the window's initial position untilsome time after the window has been created. Therefore we decided onthe following behavior, both under Windows and under UNIX/X11:When you create a window with position (x,y) and size (w,h), theupper left hand corner of the outside of the window (the non-clientarea) is at (x,y) and the size of the drawable (client) area is (w,h).The coordinates taken by glutInitPosition andglutPositionWindow, as well as the coordinates provided byfreeglut when it calls the glutPositionFunc callback,specify the top-left of the non-client area of the window. By defaultonly positive-signed coordinates are supported. If GLUT_ALLOW_NEGATIVE_WINDOW_POSITIONis enabled, then negative coordinates are supported. An exceptionfor glutPositionWindow exists as it's always supported negativewindow coordinates.When you query the size and position of the window usingglutGet, freeglut will return the size of the drawablearea--the (w,h) that you specified when you created the window--and thecoordinates of the upper left hand corner of the drawable (client)area--which is NOT the (x,y) position of the window you specifiedwhen you created it.

GLUT was created as a tool to help teach OpenGL programming. To simplifydevelopment, callbacks were used for handling display, input, and otherevents. But at the time it was developed, the purpose, or for some other unknown reason, the callbacks lacked any user-provided data argument.This has caused considerable difficulties for any significantly advancedusage of GLUT, and now freeglut. This has prevented any attempt to wrap freeglut in a C++ wrapper, make per-window, per-callback datastructure, and potentially made it undesirable to modern C developers whotend to be well versed in "don't use globals". To combat thesecomplaints and issues, many callbacks (with some deprecated callbacks excluded) support user-data callbacks provided through additionalfunctions provided in freeglut. All callbacks that support user-datacallbacks are marked as such.

The general rule to follow is to take the freeglut callback function and append "Ucall" to the end of the function, add an additional void*argument to the end of the argument list of both the freeglut functionand the callback function. This will pass the user-data to the callback when it'sinvoked.

Since the freeglut library was developed in order to update GLUT,it is natural that there will be some differences between the two.Each function in the API notes any differences between the GLUT and the freeglut function behaviours. The important ones are summarizedhere.

One of the commonest complaints about the GLUT library was that once anapplication called glutMainLoop, it never got control back.There was no way for an application to loop in GLUT for a while, possiblyas a subloop while a specific window was open, and then return to the callingfunction. A new function, glutMainLoopEvent, has been addedto allow this functionality. Another function, glutLeaveMainLoop,has also been added to allow the application to tell freeglut to cleanup and close down.

Several new callbacks have been added and several callbacks which were specificto Silicon Graphics hardware have not been implemented. Most or allof the new callbacks are listed in the GLUT Version 4 "glut.h" header filebut did not make it into the documentation. The new callbacks consistof regular and special key release callbacks, a joystick callback, a menustate callback (with one argument, distinct from the menu status callbackwhich has three arguments), a window status callback (also with oneargument), and a window position callback. Unsupported callbacks arethe two Tablet callbacks. If the user has a need for an unsupportedcallback he should contact the freeglut development team.

The glutInitWindowPosition and glutInitWindowSizefunctions specify a desired position and size for windows thatfreeglut will create in the future.The position is measured in pixels from the upper left hand corner of thescreen, with "x" increasing to the right and "y" increasing towards the bottomof the screen. The size is measured in pixels. freeglutdoes not promise to follow these specifications in creating its windows,but it certainly makes an attempt to.

The position and size of a window are a matter of some subtlety. Mostwindows have a usable area surrounded by a border and with a title baron the top. The border and title bar are commonly called "decorations."The position of the window unfortunately varies with the operating system.On both Linux and Windows, you specify the coordinates of the upperleft-hand corner of the window's decorations. Also for both operatingsystems, the size of the window is the size of the usable interior.

With glutGet information can be acquired about the currentwindow's size, position and decorations. Note however that according tofreeglut's conventions, the informationreturned about the window coordinates does not correspond to thecoordinates used when setting window position. In addition, GLUT onlyaccepts positive window coordinates, and ignores all negative windowcoordinates. But if GLUT_ALLOW_NEGATIVE_WINDOW_POSITION is enabled,then negative window coordinates can be used. This is useful formulti-montitor setups where the second monitor may be in the negativedesktop space of the primary monitor, as now the window can be placedon the additional monitors. Furthermore, this flag also determines how negative coordinates and sizes are interpreted for subwindows.

Windows has some additional quirks which the application programmershould know about. First, the minimum y-coordinateof a window decoration is zero. (This is a feature of freeglutand can be adjusted if so desired.) Second, there appears to be aminimum window width on Windows which is 104 pixels. The user may specifya smaller width, but the Windows system calls ignore it. It is alsoimpossible to make a window narrower than this by dragging on its corner.

glutInitDisplayString support is limited: any of the tokens recognizedby GLUT are also recognized by freeglut, but any statements withcomparators cannot (yet: do help developthis!) be handled. Any spec (comparator and value) after the tokenis ignored. However, many of these values can be set with glutSetOptionfor now...

The glutInitErrorFunc and glutInitWarningFuncfunctions specify callbacks that will be called upon warnings and errorsissued from within freeglut so that the user can deal with these.Useful for rerouting to another output sink (e.g., logging) and also toavoid exit(1) being called upon error. As with other glutInit*functions, these can be set before glutInit is called, so any outputfrom the library can be handled by the user.

The users callback is passed a format string and a variable argumentlist that can be passed to functions such as printf.

Note that there are the preprocessor definitionsFREEGLUT_PRINT_ERRORS and FREEGLUT_PRINT_WARNINGS,which affect freeglut's warning and error behavior when no usercallback is defined. If defined at library (not client app!) compiletime--by default it is, warnings and errors are printed tostderr. If not defined, warnings and errors are muted (notprinted to stderr), though errors still trigger deinitialization andexit. Whether FREEGLUT_PRINT_ERRORS andFREEGLUT_PRINT_WARNINGS is defined does not affect whether theclient callback is called, it only affects whether warnings and errorsare printed to stderr when no callback is defined. e24fc04721