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 glut(3GLUT)                        GLUT                         glut(3GLUT)
 GLUT                                                                   GLUT

                                     3.7



 NAME
      glut - an introduction to the OpenGL Utility Toolkit

 SYNOPSIS
      #include <GL/glut.h>

 DESCRIPTION
      The OpenGL Utility Toolkit (GLUT) is a programming interface with ANSI
      C and FORTRAN bindings for writing window system independent OpenGL
      programs. The toolkit supports the following functionality:

           Multiple windows for OpenGL rendering.

           Callback driven event processing.

           Sophisticated input devices.

           An ``idle'' routine and timers.

           A simple, cascading pop-up menu facility.

           Utility routines to generate various solid and wire frame
           objects.

           Support for bitmap and stroke fonts.

           Miscellaneous window management functions, including managing
           overlays. An ANSI C implementation of GLUT for the X Window
           System has been implemented by the author. Windows NT and OS/2
           versions of GLUT are also available.

 BACKGROUND
      One of the major accomplishments in the specification of OpenGL was
      the isolation of window system dependencies from OpenGL's rendering
      model. The result is that OpenGL is window system independent.

      Window system operations such as the creation of a rendering window
      and the handling of window system events are left to the native window
      system to define. Necessary interactions between OpenGL and the window
      system such as creating and binding an OpenGL context to a window are
      described separately from the OpenGL specification in a window system
      dependent specification. For example, the GLX specification describes
      the standard by which OpenGL interacts with the X Window System.

      The predecessor to OpenGL is IRIS GL. Unlike OpenGL, IRIS GL does
      specify how rendering windows are created and manipulated. IRIS GL's
      windowing interface is reasonably popular largely because it is simple
      to use. IRIS GL programmers can worry about graphics programming
      without needing to be an expert in programming the native window



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 glut(3GLUT)                        GLUT                         glut(3GLUT)
 GLUT                                                                   GLUT

                                     3.7



      system.  Experience also demonstrated that IRIS GL's windowing
      interface was high-level enough that it could be retargeted to
      different window systems.  Silicon Graphics migrated from NeWS to the
      X Window System without any major changes to IRIS GL's basic windowing
      interface.

      Removing window system operations from OpenGL is a sound decision
      because it allows the OpenGL graphics system to be retargeted to
      various systems including powerful but expensive graphics workstations
      as well as mass-production graphics systems like video games, set-top
      boxes for interactive television, and PCs.

      Unfortunately, the lack of a window system interface for OpenGL is a
      gap in OpenGL's utility. Learning native window system APIs such as
      the X Window System's Xlib or Motif can be daunting. Even those
      familiar with native window system APIs need to understand the
      interface that binds OpenGL to the native window system. And when an
      OpenGL program is written using the native window system interface,
      despite the portability of the program's OpenGL rendering code, the
      program itself will be window system dependent.

      Testing and documenting OpenGL's functionality lead to the development
      of the tk and aux toolkits. The aux toolkit is used in the examples
      found in the OpenGL Programming Guide. Unfortunately, aux has numerous
      limitations and its utility is largely limited to toy programs. The tk
      library has more functionality than aux but was developed in an ad hoc
      fashion and still lacks much important functionality that IRIS GL
      programmers expect, like pop-up menus and overlays.

      GLUT is designed to fill the need for a window system independent
      programming interface for OpenGL programs. The interface is designed
      to be simple yet still meet the needs of useful OpenGL programs.
      Features from the IRIS GL, aux, and tk interfaces are included to make
      it easy for programmers used to these interfaces to develop programs
      for GLUT.

 PHILOSPHY
      GLUT simplifies the implementation of programs using OpenGL rendering.
      The GLUT application programming interface (API) requires very few
      routines to display a graphics scene rendered using OpenGL. The GLUT
      API (like the OpenGL API) is stateful. Most initial GLUT state is
      defined and the initial state is reasonable for simple programs.

      The GLUT routines also take relatively few parameters. No pointers are
      returned. The only pointers passed into GLUT are pointers to character
      strings (all strings passed to GLUT are copied, not referenced) and
      opaque font handles.

      The GLUT API is (as much as reasonable) window system independent. For



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 glut(3GLUT)                        GLUT                         glut(3GLUT)
 GLUT                                                                   GLUT

                                     3.7



      this reason, GLUT does not return any native window system handles,
      pointers, or other data structures. More subtle window system
      dependencies such as reliance on window system dependent fonts are
      avoided by GLUT; instead, GLUT supplies its own (limited) set of
      fonts.

      For programming ease, GLUT provides a simple menu sub-API. While the
      menuing support is designed to be implemented as pop-up menus, GLUT
      gives window system leeway to support the menu functionality in
      another manner (pull-down menus for example).

      Two of the most important pieces of GLUT state are the current window
      and current menu. Most window and menu routines affect the current
      window or menu respectively. Most callbacks implicitly set the current
      window and menu to the appropriate window or menu responsible for the
      callback. GLUT is designed so that a program with only a single window
      and/or menu will not need to keep track of any window or menu
      identifiers.  This greatly simplifies very simple GLUT programs.

      GLUT is designed for simple to moderately complex programs focused on
      OpenGL rendering. GLUT implements its own event loop. For this reason,
      mixing GLUT with other APIs that demand their own event handling
      structure may be difficult. The advantage of a builtin event dispatch
      loop is simplicity.

      GLUT contains routines for rendering fonts and geometric objects,
      however GLUT makes no claims on the OpenGL display list name space.
      For this reason, none of the GLUT rendering routines use OpenGL
      display lists. It is up to the GLUT programmer to compile the output
      from GLUT rendering routines into display lists if this is desired.

      GLUT routines are logically organized into several sub-APIs according
      to their functionality. The sub-APIs are:

      Initialization.
           Command line processing, window system initialization, and
           initial window creation state are controlled by these routines.

      Beginning Event Processing.
           This routine enters GLUT's event processing loop. This routine
           never returns, and it continuously calls GLUT callbacks as
           necessary.

      Window Management.
           These routines create and control windows.

      Overlay Management.
           These routines establish and manage overlays for windows.




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 glut(3GLUT)                        GLUT                         glut(3GLUT)
 GLUT                                                                   GLUT

                                     3.7



      Menu Management.
           These routines create and control pop-up menus.

      Callback Registration.
           These routines register callbacks to be called by the GLUT event
           processing loop.

      Color Index Colormap Management.
           These routines allow the manipulation of color index colormaps
           for windows.

      State Retrieval.
           These routines allows programs to retrieve state from GLUT.

      Font Rendering.
           These routines allow rendering of stroke and bitmap fonts.

      Geometric Shape Rendering.
           These routines allow the rendering of 3D geometric objects
           including spheres, cones, icosahedrons, and teapots.

 CONVENTIONS
      GLUT window and screen coordinates are expressed in pixels. The upper
      left hand corner of the screen or a window is (0,0). X coordinates
      increase in a rightward direction; Y coordinates increase in a
      downward direction. Note: This is inconsistent with OpenGL's
      coordinate scheme that generally considers the lower left hand
      coordinate of a window to be at (0,0) but is consistent with most
      popular window systems.

      Integer identifiers in GLUT begin with one, not zero. So window
      identifiers, menu identifiers, and menu item indexes are based from
      one, not zero.

      In GLUT's ANSI C binding, for most routines, basic types (int, char*)
      are used as parameters. In routines where the parameters are directly
      passed to OpenGL routines, OpenGL types (GLfloat) are used.

      The header files for GLUT should be included in GLUT programs with the
      following include directive:
      #include <GL/glut.h>
      Because a very large window system software vendor (who will remain
      nameless) has an apparent inability to appreciate that OpenGL's API is
      independent of their window system API, portable ANSI C GLUT programs
      should not directly include <GL/gl.h> or <GL/glu.h>. Instead, ANSI C
      GLUT programs should rely on <GL/glut.h> to include the necessary
      OpenGL and GLU related header files.

      The ANSI C GLUT library archive is typically named libglut.a on Unix



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 glut(3GLUT)                        GLUT                         glut(3GLUT)
 GLUT                                                                   GLUT

                                     3.7



      systems. GLUT programs need to link with the system's OpenGL and GLUT
      libraries (and any libraries these libraries potentially depend on). A
      set of window system dependent libraries may also be necessary for
      linking GLUT programs. For example, programs using the X11 GLUT
      implementation typically need to link with Xlib, the X extension
      library, possibly the X Input extension library, the X miscellaneous
      utilities library, and the math library. An example X11/Unix compile
      line would look like:
      cc -o foo foo.c -lglut -lGLU -lGL -lXmu -lXi -lXext -lX11 -lm

 SEE ALSO
      glutAddMenuEntry, glutAddSubMenu, glutAttachMenu, glutBitmapCharacter,
      glutBitmapWidth, glutButtonBoxFunc, glutChangeToMenuEntry,
      glutChangeToSubMenu, glutCopyColormap, glutCreateMenu,
      glutCreateSubWindow, glutCreateWindow, glutDestroyMenu,
      glutDestroyWindow, glutDeviceGet, glutDialsFunc, glutDisplayFunc,
      glutEntryFunc, glutEstablishOverlay, glutExtensionSupported,
      glutFullScreen, glutGet, glutGetColor, glutGetModifiers, glutIdleFunc,
      glutInit, glutInitDisplayMode, glutInitWindowPosition,
      glutKeyboardFunc, glutLayerGet, glutMainLoop, glutMenuStatusFunc,
      glutMotionFunc, glutMouseFunc, glutOverlayDisplayFunc, glutPopWindow,
      glutPositionWindow, glutPostOverlayRedisplay, glutPostRedisplay,
      glutRemoveMenuItem, glutRemoveOverlay, glutReshapeFunc,
      glutReshapeWindow, glutSetColor, glutSetCursor, glutSetMenu,
      glutSetWindow, glutSetWindowTitle, glutShowOverlay, glutShowWindow,
      glutSolidCone, glutSolidCube, glutSolidDodecahedron,
      glutSolidIcosahedron, glutSolidOctahedron, glutSolidSphere,
      glutSolidTeapot, glutSolidTetrahedron, glutSolidTorus,
      glutSpaceballButtonFunc, glutSpaceballMotionFunc,
      glutSpaceballRotateFunc, glutSpecialFunc, glutStrokeCharacter,
      glutStrokeWidth, glutSwapBuffers, glutTabletButtonFunc,
      glutTabletMotionFunc, glutTimerFunc, glutUseLayer, glutVisibilityFunc,

 REFERENCES
      Mark Kilgard, Programming OpenGL for the X Window System, Addison-
      Wesley, ISBN 0-201-48359-9, 1996.

      Mark Kilgard, The OpenGL Utility Toolkit (GLUT) Programming Interface
      API Version 3 (the official GLUT specification).

 WEB REFERENCES
      Main GLUT page
      http://reality.sgi.com/mjk/glut3/glut3.html

      GLUT Frequently Asked Question list
      http://reality.sgi.com/mjk/glut3/glut-faq.html

      The OpenGL Utility Toolkit (GLUT) Programming Interface API Version 3
      http://reality.sgi.com/mjk/spec3/spec3.html



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 glut(3GLUT)                        GLUT                         glut(3GLUT)
 GLUT                                                                   GLUT

                                     3.7



      http://reality.sgi.com/mjk/glut3/glut-3.spec.ps.gz

      OpenGL and X: An OpenGL Toolkit article (PostScript)
      http://reality.sgi.com/mjk/glut3/glut.column1.ps.gz

 AUTHOR
      Mark J. Kilgard (mjk@nvidia.com)













































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