Winteracter

OpenGL^TM

Overview

Developed originally by Silicon Graphics Inc., OpenGL is a 2D/3D graphics library which is available on most Win32, Unix and Linux systems. OpenGL's main strengths are in the areas of 3 dimensional visualisation and animation.

Calls to OpenGL routines in the GL and GLU libraries (v1.10) can be included in Winteracter programs. While other OpenGL interfaces exist for use from Fortran based applications, the Winteracter OpenGL interface offers some significant advantages

	OpenGL graphics can be routed to a window, memory bitmap or dialog field. Other interfaces typically just offer output to a window.
	OpenGL images can be printed via IGrPrintImage. Other interfaces do not typically offer printing facilities.
	The full range of menu types (horizontal menu bar, toolbar and floating menus are all available). Some other interfaces only offer floating menus.
	All the other Winteracter facilities are simultaneously available, combining state of the art 3D graphics, with extensive user-interface and scientific graph plotting capabilities.
	Text handling has been added (see below).

Winteracter's interface to OpenGL consists of two main components:

	A routine called WglSelect which selects a target drawing surface for OpenGL output.
	A module called OPENGL which provides a Fortran 9x interface to the various OpenGL graphics routines. The routine names are the same as the C originals. Fortran 90 data types are also defined which are directly analagous to the C equivalents. Together, these allow easy translation of C based OpenGL code to Fortran 90/95.

A Winteracter-based program therefore needs to specify USE OPENGL in each program unit which will call OpenGL. A call to WglSelect will be required to specify the target drawing surface.

Supported Platforms

Win32 programs which call OpenGL routines require the presence of two Windows system DLL's called OPENGL32.DLL and GLU32.DLL (the so-called GL and GLU libraries). These are usually located in the Windows SYSTEM or SYSTEM32 directory. These are provided under Windows NT/2000/XP/98/Me and Windows 95 OSR2. Users of Windows 95 release 1 will need to download the OpenGL DLL's from Microsoft's web site.

OpenGL support in Windows is 'generic'. In other words, it will work on any of the systems noted above. Special 'OpenGL compatible' video hardware is not required. Accelerated OpenGL support on PC video hardware has become much more widespread in recent times, but the generic software based interface can still be used where this is not available. Where accelerated facilities exist, some older drivers may only provide full-screen support or only support certain colour depths. However, substantial performance benefits can be expected with suitable combinations of 3D video hardware and OpenGL-aware drivers.

OpenGL is also supported under Linux. Typically, this is achieved by linking with the Mesa workalike library.

Documentation and Examples

We recommend use of a suitable reference book when writing applications which use OpenGL. However, since most of the available reference material is C oriented, the supplied on-line documentation includes brief Fortran oriented descriptions of all of the supported OpenGL functions. A selection of example programs are also included to illustrate the use of OpenGL in Winteracter-based applications.

Text Handling

Since OpenGL provides no text output facilities as standard, Winteracter includes a set of text support routines which are closely modelled on its own graphics text handling facilities. These OpenGL text support functions provide access to any True Type font under Windows and to a handful of built-in software-based vector fonts under both Windows and Linux.

Acknowledgements

OpenGL is a trademark of Silicon Graphics Inc.

The OPENGL module included with Winteracter is a derivation of f90gl, the official Fortran 90 OpenGL interface written by William F. Mitchell of the Mathematical and Computational Sciences Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA. While ISS provided some minor assistance in the Win32 implementation of the f90gl interface, the credit for that interface belongs to William Mitchell. The Winteracter implementation of the OpenGL interface differs from f90gl in several ways:

	The internal Fortran/C calling interfaces have been revised to ensure their correct operation with all the Win32 Fortran 9x compilers supported by Winteracter.
	The GLUT interface has been omitted since this is not required in Winteracter based programs.
	The various separate modules in the f90gl interface have been consolidated into a single module. It is only necessary to add a single USE OPENGL statement per program unit to gain access to all the OpenGL routines and data types.
	The additional object code libraries which accompany the f90gl interface are subsumed in the winter.lib Winteracter library in most Win32 implementations, thereby simplifying the linking procedure. The Linux version provides a separate libwintGL.a OpenGL support library.
	Support for implementation-specific OpenGL extension routines can optionally be built into f90gl via a series of pre-processor switches. However, since this involves rebuilding the interface for each target OpenGL implementation (which in turn requires a C compiler) this support has been omitted from the Winteracter OpenGL interface.