openGL and JOGL

JOGL Components and GLEventListener

The first thing we need to do to get JOGL into an AWT application is to create a GLCanvas component. (The Swing version does not currently enjoy hardware-accelerated rendering, that means it is slow):

      GLCapabilities caps = new GLCapabilities();
      caps.setDoubleBuffered( true );
      caps.setHardwareAccelerated( true );

      canvas = new GLCanvas( caps );

We have to ask this GLCapabilities object for a component that is tuned to the characteristics of the current display, such as its color depth.

The next thing we have to do with our canvas is to register it as a GLEventListener:

      canvas.addGLEventListener(this);

The GLEventListener interface defines four methods:

init (GLDrawable drawable):
called when OpenGL is initialized, and thus useful for any one-time-only setup work.
display (GLDrawable drawable):
a request for the component to draw itself.
reshape (GLDrawable drawable, int i, int x, int width, int height):
signals that the component's location or size has been changed.
displayChanged (GLDrawable drawable, boolean modeChanged, boolean deviceChanged):
used to signal that the display mode or device has changed, such as when the user changes the color depth from 16-bit to 32-bit color or to indicate that the window has been dragged from one monitor (a "device") to another.

In the sample application, init() is used for debug and to set the color for erasing the canvas (to white or black):

GL gl = drawable.getGL(); 
gl.glClearColor( 1.0f, 1.0f, 1.0f, 1.0f );

The GL class is "the basic interface to OpenGL." Think of it as a handle for making openGL (gl.h) method calls.
glu.-type calls to glu.h are made via the GLU object also retrieved from the GLDrawable.

The reshape() method sets or re-sets its size and "viewport," which represents what part of the component is being drawn into:

GL gl = drawable.getGL();
gl.glMatrixMode(GL.GL_PROJECTION);
gl.glLoadIdentity();
gl.glFrustum( -0.1f, 0.1f, -0.1f, 0.1f, 0.2f, 2.0f );

GL gl = drawable.getGL(); 
GLU glu = drawable.getGLU(); 
gl.glViewport( 0, 0, width, height ); 
gl.glMatrixMode( GL.GL_PROJECTION );  
gl.glLoadIdentity(); 
glu.gluOrtho2D( 0.0, 450.0, 0.0, 375.0);

The display() method performs the drawing after init() and reshape() at startup. It could also be called by JOGL's Animator class, which exists to call display() repeatedly from a loop. This has obvious use for games, media, and other applications -- they perform animation by slightly changing the component on each successive call to display().

display() also erases the component with:

gl.glClear(GL.GL_COLOR_BUFFER_BIT)