JOGL information

CS 428 - JOGL information

Online resources

JOGL API (description and downloads)
JSR 231: Java Binding for the OpenGL API

Why are we using JOGL?

OpenGL is perhaps most directly used with C/C++. JOGL serves two purposes. First, it provides "wrapper functions" via JNI so you can call OpenGL functions from Java. Second, it extends classes in Java.awt to allow for the creation of OpenGL windows. (From C/C++, this is typically done with a GUI library such as GLUT, Tck/Tk, Motif, or the MFC in Visual C++ in Windows).

Using OpenGL with JOGL

The use of OpenGL via JOGL is quite simple, and can be briefly summarized as:

You need to import the appropriate classes (This will be done for you in the provided skeleton code.)
All GL function calls are prefixed with "gl."
All GLU function calls are prefixed with "glu."
OpenGL constants/enumerations are prefixed with "GL."
Java types are used in place of OpenGL types, although explicit casts or type specifiers will be required

For example, the following fragment of C code:

      glBegin(GL_POLYGON);
      glVertex3f(0.25, 0.25, 0.0);
      glVertex3f(0.75, 0.25, 0.0);
      glVertex3f(0.75, 0.75, 0.0);
      glVertex3f(0.25, 0.75, 0.0);
      glEnd();

would be written in Java as:

      gl.glBegin(GL.GL_POLYGON);
      gl.glVertex3f(0.25f, 0.25f, 0.0f);
      gl.glVertex3f(0.75f, 0.25f, 0.0f);
      gl.glVertex3f(0.75f, 0.75f, 0.0f);
      gl.glVertex3f(0.25f, 0.75f, 0.0f);
      gl.glEnd();

Notice the explicit type specifications (the f's) in the arguments to gl.glVertex3f(). As a result, it's probably easier to use double for everything:

      gl.glBegin(GL.GL_POLYGON);
      gl.glVertex3d(0.25, 0.25, 0.0);
      gl.glVertex3d(0.75, 0.25, 0.0);
      gl.glVertex3d(0.75, 0.75, 0.0);
      gl.glVertex3d(0.25, 0.75, 0.0);
      gl.glEnd();

There are also some differences in argument structure, in particular when passing arrays to OpenGL functions. For instance, when using the vector versions of vertex functions, like gl.glVertex3dv(), or gl.glColor3dv(), you need to add a second argument with the value zero:

      double[] p = { 1.0, 1.0, 2.0 };

      gl.glVertex3dv(p, 0);

or when specifying a clipping plane, a third argument of zero:

      double[] eqn = { 0.0, 1.0, 0.0, 1.5 };

      gl.glClipPlane(GL.GL_CLIP_PLANE0, eqn, 0);

The skeleton code you'll be using defines gl and (when needed) glu.

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