Controls the display callback for the current window. When GLUT determines that the normal plane for the window needs to be redisplayed, the display callback for the window is called. Before the callback, the current window is set to the window needing to be redisplayed and (if no overlay display callback is registered) the layer in use is set to the normal plane. The entire normal plane region should be redisplayed in response to the callback (this includes ancillary buffers if your program depends on their state).

GLUT determines when the display callback should be triggered based on the window's redisplay state. The redisplay state for a window can be either set explicitly by calling postRedisplay or implicitly as the result of window damage reported by the window system. Multiple posted redisplays for a window are coalesced by GLUT to minimize the number of display callbacks called.

When an overlay is established for a window, but there is no overlay display callback registered, the display callback is used for redisplaying both the overlay and normal plane (that is, it will be called if either the redisplay state or overlay redisplay state is set). In this case, the layer in use is not implicitly changed on entry to the display callback.

See overlayDisplayCallback to understand how distinct callbacks for the overlay and normal plane of a window may be established.

When a window is created, no display callback exists for the window. It is the responsibility of the programmer to install a display callback for the window before the window is shown. A display callback must be registered for any window that is shown. If a window becomes displayed without a display callback being registered, a fatal error occurs. There is no way to "deregister" a display callback (though another callback routine can always be registered).

Upon return from the display callback, the normal damaged state of the window (see damaged) is cleared. If there is no overlay display callback registered the overlay damaged state of the window (see damaged) is also cleared.

Controls the overlay display callback for the current window. The overlay display callback is functionally the same as the window's display callback except that the overlay display callback is used to redisplay the window's overlay.

When GLUT determines that the overlay plane for the window needs to be redisplayed, the overlay display callback for the window is called. Before the callback, the current window is set to the window needing to be redisplayed and the layer in use is set to the overlay. The entire overlay region should be redisplayed in response to the callback (this includes ancillary buffers if your program depends on their state).

GLUT determines when the overlay display callback should be triggered based on the window's overlay redisplay state. The overlay redisplay state for a window can be either set explicitly by calling postOverlayRedisplay or implicitly as the result of window damage reported by the window system. Multiple posted overlay redisplays for a window are coalesced by GLUT to minimize the number of overlay display callbacks called.

Upon return from the overlay display callback, the overlay damaged state of the window (see damaged) is cleared.

Initially there is no overlay display callback registered when an overlay is established. See displayCallback to understand how the display callback alone is used if an overlay display callback is not registered.

Controls the reshape callback for the current window. The reshape callback is triggered when a window is reshaped. A reshape callback is also triggered immediately before a window's first display callback after a window is created or whenever an overlay for the window is established. The parameter of the callback specifies the new window size in pixels. Before the callback, the current window is set to the window that has been reshaped.

If a reshape callback is not registered for a window or reshapeCallback is set to Nothing (to deregister a previously registered callback), the default reshape callback is used. This default callback will simply call

 viewport (Position 0 0) (Size width height)

on the normal plane (and on the overlay if one exists).

If an overlay is established for the window, a single reshape callback is generated. It is the callback's responsibility to update both the normal plane and overlay for the window (changing the layer in use as necessary).

When a top-level window is reshaped, subwindows are not reshaped. It is up to the GLUT program to manage the size and positions of subwindows within a top-level window. Still, reshape callbacks will be triggered for subwindows when their size is changed using windowSize.

Controls the visibility callback for the current window. The visibility callback for a window is called when the visibility of a window changes.

If the visibility callback for a window is disabled and later re-enabled, the visibility status of the window is undefined; any change in window visibility will be reported, that is if you disable a visibility callback and re-enable the callback, you are guaranteed the next visibility change will be reported.

Controls the mouse enter/leave callback for the current window. Note that some window systems may not generate accurate enter/leave callbacks.

X Implementation Notes: An X implementation of GLUT should generate accurate enter/leave callbacks.

Controls the Spaceball callback for the current window. The Spaceball callback for a window is called when the window has Spaceball input focus (normally, when the mouse is in the window) and the user generates Spaceball translations, rotations, or button presses. The number of available Spaceball buttons can be determined with numSpaceballButtons.

Registering a Spaceball callback when a Spaceball device is not available has no effect and is not an error. In this case, no Spaceball callbacks will be generated.

Controls the dial & button box callback for the current window. The dial & button box button callback for a window is called when the window has dial & button box input focus (normally, when the mouse is in the window) and the user generates dial & button box button presses or dial changes. The number of available dial & button box buttons and dials can be determined with numDialsAndButtons.

Registering a dial & button box callback when a dial & button box device is not available is ineffectual and not an error. In this case, no dial & button box button will be generated.

Controls the tablet callback for the current window. The tablet callback for a window is called when the window has tablet input focus (normally, when the mouse is in the window) and the user generates tablet motion or button presses. The number of available tablet buttons can be determined with numTabletButtons.

Registering a tablet callback when a tablet device is not available is ineffectual and not an error. In this case, no tablet callbacks will be generated.

Controls the joystick callback for the current window. The joystick callback is called either due to polling of the joystick at the uniform timer interval specified (if > 0) or in response to an explicit call of forceJoystickCallback.

X Implementation Notes: Currently GLUT has no joystick support for X11.