Actions and state variables in this module are used to initialize GLUT state. The primary initialization routine is initialize, which should only be called exactly once in a GLUT program. No other GLUT or OpenGL actions should be called before initialize, apart from getting or setting the state variables in this module.

The reason is that these state variables can be used to set default window initialization state that might be modified by the command processing done in initialize. For example, initialWindowSize can be set to (Size 400 400) before initialize is called to indicate 400 by 400 is the program's default window size. Setting the initial window size or position before initialize allows the GLUT program user to specify the initial size or position using command line arguments.

Controls the initial window position. Windows created by createWindow will be requested to be created with the current initial window position. The initial value of the initial window position GLUT state is Size (-1) (-1). If either the X or Y component of the initial window position is negative, the actual window position is left to the window system to determine.

The intent of the initial window position is to provide a suggestion to the window system for a window's initial position. The window system is not obligated to use this information. Therefore, GLUT programs should not assume the window was created at the specified position.

Controls the initial window size. Windows created by createWindow will be requested to be created with the current initial window size. The initial value of the initial window size GLUT state is Size 300 300. If either the width or the height component of the initial window size is non-positive, the actual window size is left to the window system to determine.

The intent of the initial window size is to provide a suggestion to the window system for a window's initial size. The window system is not obligated to use this information. Therefore, GLUT programs should not assume the window was created at the specified size. A GLUT program should use the window's reshape callback to determine the true size of the window.

Controls the initial display mode used when creating top-level windows, subwindows, and overlays to determine the OpenGL display mode for the to-be-created window or overlay.

Note that RGBAMode selects the RGBA color model, but it does not request any bits of alpha (sometimes called an alpha buffer or destination alpha) be allocated. To request alpha, specify WithAlphaComponent. The same applies to LuminanceMode.

Controls the initial display mode used when creating top-level windows, subwindows, and overlays to determine the OpenGL display mode for the to-be-created window or overlay. It is described by a list of zero or more capability descriptions, which are translated into a set of criteria used to select the appropriate frame buffer configuration. The criteria are matched in strict left to right order of precdence. That is, the first specified criterion (leftmost) takes precedence over the later criteria for non-exact criteria (IsGreaterThan, IsLessThan, etc.). Exact criteria (IsEqualTo, IsNotEqualTo) must match exactly so precedence is not relevant.

Unspecified capability descriptions will result in unspecified criteria being generated. These unspecified criteria help initialDisplayCapabilities behave sensibly with terse display mode descriptions.

Here is an example using initialDisplayCapabilities:

    initialDisplayCapabilities $= [ With  DisplayRGB,
                                    Where DisplayDepth IsAtLeast 16,
                                    With  DisplaySamples,
                                    Where DisplayStencil IsNotLessThan 2,
                                    With  DisplayDouble ]
 

The above call requests a window with an RGBA color model (but requesting no bits of alpha), a depth buffer with at least 16 bits of precision but preferring more, multisampling if available, at least 2 bits of stencil (favoring less stencil to more as long as 2 bits are available), and double buffering.