OpenGL

OpenGL [1] is:

• is a library for programming of 2D and 3D graphics.
• is established as an industry standard and reference standard.
• is developed by Silicon Graphics.
• has a long history under other names, GL.
• was developed under control of an Architecture Review Board, which now is a part of The Khronos Group. [2]

OpenGL is continuously developed, with new versions. Latest version, may 2009, is 3.1. One major addition to the OpenGL concept is OpenGL Shading Language [3] . OpenGL is developed as platform independent package and runs on a lot of platforms: MS-Windows NT/2000/95/Vista, MS-.Net, Linux, Unix, MacOS.

OpenGL is a flat library. It is not object-oriented and it has no standardized export or import of graphical models. OpenGL is often referred to as a "state machine": We specify a lot of details as transformations, eye point, perspective, materials etc. When all this states are set, we start rendering.That is we send our point-sequences in a pipeline through the state machine where all our settings influence the result.

There are lots of material, examples and tutoriels, available on the net. Some sources are:

• LightHouse3d OpenGL-tutorial [4]
• NEHE, NeonHelium Productions [5]

Language bindings

We can use OpenGL from a lot of languages, C, C++, C#, Fortran, Java, Python,.... How the library is reached from the language depends on the implementation of the language binding. In Java/JOGL we work against OpenGL as an object. That means that we typically do this:

  // get the OpenGL object associated with a drawing context
  GL gl = drawable.getGL();
  ...
  // use it
  gl.glEnable(GL.GL_LIGHTING);

In a typical C++ environment we do like this

  // we have linked to OpenGL and we use it
  glEnable(GL_LIGHTING);

It is important to notice that as a programmer it is easy to move sequences of source code from C/C++ to Java since most examples found in books or on the net is written in C/C++. Basically we add the "gl." and "GL.", and there are a few syntactical differences in how we define arrays, and JOGL has a few minor changes in how we use arrays. In Java:

 float ambient[] = {1.0f,1.0f,1.0f,1.0f };
 gl.glLightfv(GL.GL_LIGHT0, GL.GL_AMBIENT,ambient,0);

In C++

 GLfloat ambient[] = {0.2f,0.2f,0.2f,1.0f };
 glLightfv(GL_LIGHT0, GL_AMBIENT, ambient);

More than gl

It is important to be aware of 3 additional libraries in the OpenGL - family.

glu

gl utilities is a set of methods that are based on gl, can be expressed in a series of gl-calls, and is supported to make some standard operations simpler for us as programmers. Typically:

GLU glu = new GLU();
...
glu.gluPerspective(45.0f, h, 1.0, 20.0);

glut

The OpenGL Utility Toolkit is basically a set of routines that manage platform independent simple windowing and mousing. We have access to glut when programming Java/JOGL. The Utah Teapot [6] is included in glut:

GLUT glut=new GLUT();
...
glut.glutSolidTeapot(1.0);

wgl

Windows specific routines for OpenGL. The purpose is to manage window specific concepts. One usage is 3D text based on Windows font descriptions.