import javax.media.opengl.GL;
import javax.media.opengl.GL2;
import javax.media.opengl.GLContext;
import javax.media.opengl.GLDrawableFactory;
import javax.media.opengl.GLProfile;
import javax.media.opengl.glu.GLU;

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.opengl.GLCanvas;
import org.eclipse.swt.opengl.GLData;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Listener;


public class Triangle extends Composite {

	GLCanvas glcanvas;

	/**
	 * @param arg0
	 * @param arg1
	 */
	public Triangle(Composite arg0, int arg1) {
		super(arg0, arg1);
		this.setLayout(new FillLayout());

		GLData gldata = new GLData();
		gldata.doubleBuffer = true;
		// need SWT.NO_BACKGROUND to prevent SWT from clearing the window
		// at the wrong times (we use glClear for this instead)
		glcanvas = new GLCanvas( this, SWT.NO_BACKGROUND, gldata );
		glcanvas.setCurrent();
		GLProfile glprofile = GLProfile.getDefault();
		final GLContext glcontext = GLDrawableFactory.getFactory( glprofile ).createExternalGLContext();

		// fix the viewport when the user resizes the window
		glcanvas.addListener( SWT.Resize, new Listener() {
			public void handleEvent(Event event) {
				System.out.println("resize");
				Rectangle rectangle = glcanvas.getClientArea();
				glcanvas.setCurrent();
				glcontext.makeCurrent();
				setup( glcontext.getGL().getGL2(), rectangle.width, rectangle.height );
				glcontext.release();
			}
		});

		// draw the triangle when the OS tells us that any part of the window needs drawing
		glcanvas.addPaintListener( new PaintListener() {
			public void paintControl( PaintEvent paintevent ) {
				System.out.println("render");
				Rectangle rectangle = glcanvas.getClientArea();
				glcanvas.setCurrent();
				glcontext.makeCurrent();
				render(glcontext.getGL().getGL2(), rectangle.width, rectangle.height);
				glcanvas.swapBuffers();
				glcontext.release();
			}
		});
	}

	private void setup( GL2 gl2, int width, int height ) {
        gl2.glMatrixMode( GL2.GL_PROJECTION );
        gl2.glLoadIdentity();

        // coordinate system origin at lower left with width and height same as the window
        GLU glu = new GLU();
        glu.gluOrtho2D( 0.0f, width, 0.0f, height );

        gl2.glMatrixMode( GL2.GL_MODELVIEW );
        gl2.glLoadIdentity();

        gl2.glViewport( 0, 0, width, height );
    }

    private void render( GL2 gl2, int width, int height ) {
        gl2.glClear( GL.GL_COLOR_BUFFER_BIT );

        // draw a triangle filling the window
        gl2.glLoadIdentity();
        gl2.glBegin( GL.GL_TRIANGLES );
        gl2.glColor3f( 1, 0, 0 );
        gl2.glVertex2f( 0, 0 );
        gl2.glColor3f( 0, 1, 0 );
        gl2.glVertex2f( width, 0 );
        gl2.glColor3f( 0, 0, 1 );
        gl2.glVertex2f( width / 2, height );
        gl2.glEnd();
    }

	/* (non-Javadoc)
	 * @see org.eclipse.swt.widgets.Widget#dispose()
	 */
	@Override
	public void dispose() {
		glcanvas.dispose();
		super.dispose();
	}


}