/* draw a point */
/* Java's supplied classes are "imported". Here the awt (Abstract Windowing Toolkit) is imported to provide "Frame" class, which includes windowing functions
*/
import java.awt.*;

// JOGL: OpenGL functions
import net.java.games.jogl.*; 


/* Java class definition: "extends" means "inherits". So J1_0_Point is a subclass of Frame, and it inherits Frame's variables and methods. "implements" means GLEventListener is an interface, which only defines methods (init(), reshape(), display(), and displaychanged()) without implementation. J1_0_Point will implement GLEventListener's methods and use them. 
*/
public class J1_0_Point extends Frame implements GLEventListener {

	 static int HEIGHT = 400, WIDTH = 400; 
	 static GL gl; //interface to OpenGL
	 static GLCanvas canvas; // drawable in a frame


	 public J1_0_Point() { // constructor

		//1. specify a drawable: canvas
		GLCapabilities capabilities = new GLCapabilities(); 
		canvas = GLDrawableFactory.getFactory().createGLCanvas(capabilities);

		//2. listen to the events related to canvas: reshape
		canvas.addGLEventListener(this);						

		//3. add the canvas to fill the Frame container
		add(canvas, BorderLayout.CENTER);
		/* In Java, a method belongs to a class object. 
		Here the method "add" belongs to J1_0_Point's 
		instantiation, which is frame in "main" function. 
		It is equivalent to use "this.add(canvas, ...)" */

		//4. interface to OpenGL functions
		gl = canvas.getGL();				
	}
	
   
	public static void main(String[] args) {

		J1_0_Point frame = new J1_0_Point();

		//5. set the size of the frame and make it visible 
		frame.setSize(WIDTH, HEIGHT);
		frame.setVisible(true);
	}


	// Called once for OpenGL initialization
	public void init(GLDrawable drawable) { 
	
		//6. specify a drawing color: red
		gl.glColor3f(1.0f, 0.0f, 0.0f);						
	}


	// Called for handling reshaped drawing area 
	public void reshape(
		GLDrawable drawable,
		int x,
		int y,
		int width,
		int height) {

		//7. specify the drawing area (frame) coordinates										
		gl.glMatrixMode(GL.GL_PROJECTION);
		gl.glLoadIdentity();
		gl.glOrtho(0, width, 0, height, -1.0, 1.0);
	}


	// Called for OpenGL rendering every reshape
	public void display(GLDrawable drawable) {

		//8. specify to draw a point
		gl.glBegin(GL.GL_POINTS);
			gl.glVertex2i(WIDTH/2, HEIGHT/2);
		gl.glEnd();
	}


	// called if display mode or device are changed
	public void displayChanged(
		GLDrawable drawable,
		boolean modeChanged,
		boolean deviceChanged) {
	}
}