/*
 * select.java
 * This is an illustration of the selection mode and 
 * name stack, which detects whether objects which collide 
 * with a viewing volume.  First, four triangles and a 
 * rectangular box representing a viewing volume are drawn 
 * (drawScene routine).  The green triangle and yellow 
 * triangles appear to lie within the viewing volume, but 
 * the red triangle appears to lie outside it.  Then the 
 * selection mode is entered (selectObjects routine).  
 * Drawing to the screen ceases.  To see if any collisions 
 * occur, the four triangles are called.  In this example, 
 * the green triangle causes one hit with the name 1, and 
 * the yellow triangles cause one hit with the name 3.
 */

import java.awt.Frame;
import java.io.IOException;
import java.lang.String;
import java.lang.System;

import jgl.GL;
import jgl.GLCanvas;

public class select extends GLCanvas {

    /*
     * draw a triangle with vertices at (x1, y1), (x2, y2) 
     * and (x3, y3) at z units away from the origin.
     */
    private void drawTriangle (float x1, float y1, float x2, float y2, float x3, float y3, float z) {
	myGL.glBegin (GL.GL_TRIANGLES);
	myGL.glVertex3f (x1, y1, z);
	myGL.glVertex3f (x2, y2, z);
	myGL.glVertex3f (x3, y3, z);
	myGL.glEnd ();
    }

    /* draw a rectangular box with these outer x, y, and z values */
    private void drawViewVolume (float x1, float x2, float y1, float y2, float z1, float z2) {
	myGL.glColor3f (1.0f, 1.0f, 1.0f);
	myGL.glBegin (GL.GL_LINE_LOOP);
	    myGL.glVertex3f (x1, y1, -z1);
	    myGL.glVertex3f (x2, y1, -z1);
	    myGL.glVertex3f (x2, y2, -z1);
	    myGL.glVertex3f (x1, y2, -z1);
	myGL.glEnd ();

	myGL.glBegin (GL.GL_LINE_LOOP);
	    myGL.glVertex3f (x1, y1, -z2);
	    myGL.glVertex3f (x2, y1, -z2);
	    myGL.glVertex3f (x2, y2, -z2);
	    myGL.glVertex3f (x1, y2, -z2);
	myGL.glEnd ();

	myGL.glBegin (GL.GL_LINES);	/* 4 lines */
	    myGL.glVertex3f (x1, y1, -z1);
	    myGL.glVertex3f (x1, y1, -z2);
	    myGL.glVertex3f (x1, y2, -z1);
	    myGL.glVertex3f (x1, y2, -z2);
	    myGL.glVertex3f (x2, y1, -z1);
	    myGL.glVertex3f (x2, y1, -z2);
	    myGL.glVertex3f (x2, y2, -z1);
	    myGL.glVertex3f (x2, y2, -z2);
	myGL.glEnd ();
    }

    /*
     * drawScene draws 4 triangles and a wire frame
     * which represents the viewing volume.
     */
    private void drawScene () {
	myGL.glMatrixMode (GL.GL_PROJECTION);
	myGL.glLoadIdentity ();
	myGLU.gluPerspective (40.0, 4.0/3.0, 0.01, 100.0);

	myGL.glMatrixMode (GL.GL_MODELVIEW);
	myGL.glLoadIdentity ();
	myGLU.gluLookAt (7.5f, 7.5f, 12.5f, 2.5f, 2.5f, -5.0f, 0.0f, 1.0f, 0.0f);
	myGL.glColor3f (0.0f, 1.0f, 0.0f);	/* green triangle   */
	drawTriangle (2.0f, 2.0f, 3.0f, 2.0f, 2.5f, 3.0f, -5.0f);
	myGL.glColor3f (1.0f, 0.0f, 0.0f);	/* red triangle     */
	drawTriangle (2.0f, 7.0f, 3.0f, 7.0f, 2.5f, 8.0f, -5.0f);
	myGL.glColor3f (1.0f, 1.0f, 0.0f);	/* yellow triangles */
	drawTriangle (2.0f, 2.0f, 3.0f, 2.0f, 2.5f, 3.0f, 0.0f);
	drawTriangle (2.0f, 2.0f, 3.0f, 2.0f, 2.5f, 3.0f, -10.0f);
	drawViewVolume (0.0f, 5.0f, 0.0f, 5.0f, 0.0f, 10.0f);
    }

    /*
     * processHits prints out the contents of the selection array
     */
    private void processHits (int hits, int buffer []) {
	int i, j;
	int names, ptr;

	System.out.println ("hits = " + hits);
	ptr = 0;
	for (i = 0; i < hits; i++) {        /*  for each hit  */
	    names = buffer [ptr];
	    System.out.println (" number of names for hit = " + names); ptr++;
	    System.out.print ("  z1 is " + buffer [ptr] + ";"); ptr++;
	    System.out.println (" z2 is " + buffer [ptr]); ptr++;
	    System.out.print ("   the name is ");
	    for (j = 0; j < names; j++) {   /*  for each name */
		System.out.print (buffer [ptr] + " "); ptr++;
	    }
	    System.out.println ();
	}
    }

    /*
     * selectObjects "draws" the triangles in selection mode, 
     * assigning names for the triangles.  Note that the third
     * and fourth triangles share one name, so that if either 
     * or both triangles intersects the viewing/clipping volume, 
     * only one hit will be registered.
     */
    private static final int BUFSIZE = 512;

    private void selectObjects () {
	int selectBuf [] = new int [BUFSIZE];
	int hits;

	myGL.glSelectBuffer (BUFSIZE, selectBuf);
	myGL.glRenderMode (GL.GL_SELECT);

	myGL.glInitNames ();
	myGL.glPushName (0);

	myGL.glPushMatrix ();
	myGL.glMatrixMode (GL.GL_PROJECTION);
	myGL.glLoadIdentity ();
	myGL.glOrtho (0.0f, 5.0f, 0.0f, 5.0f, 0.0f, 10.0f);
	myGL.glMatrixMode (GL.GL_MODELVIEW);
	myGL.glLoadIdentity ();
	myGL.glLoadName (1);
	drawTriangle (2.0f, 2.0f, 3.0f, 2.0f, 2.5f, 3.0f, -5.0f);
	myGL.glLoadName (2);
	drawTriangle (2.0f, 7.0f, 3.0f, 7.0f, 2.5f, 8.0f, -5.0f);
	myGL.glLoadName (3);
	drawTriangle (2.0f, 2.0f, 3.0f, 2.0f, 2.5f, 3.0f, 0.0f);
	drawTriangle (2.0f, 2.0f, 3.0f, 2.0f, 2.5f, 3.0f, -10.0f);
	myGL.glPopMatrix ();
	myGL.glFlush ();

	hits = myGL.glRenderMode (GL.GL_RENDER);
	processHits (hits, selectBuf);
    }

    private void myinit () {
	myGL.glEnable (GL.GL_DEPTH_TEST);
	myGL.glShadeModel (GL.GL_FLAT);
    }

    public void display () {
    	myGL.glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
	myGL.glClear (GL.GL_COLOR_BUFFER_BIT | GL.GL_DEPTH_BUFFER_BIT);
	drawScene ();
	selectObjects ();
	myGL.glFlush ();
    }

    /* ARGSUSED1 */
    public void keyboard (char key, int x, int y) {
	switch (key) {
	    case 27:
		System.exit(0);
	    default:
		break;
	}
    }

    public void init () {
	myUT.glutInitWindowSize (200, 200);
	myUT.glutInitWindowPosition (0, 0);
	myUT.glutCreateWindow (this);
	myinit ();
	myUT.glutDisplayFunc ("display");
	myUT.glutKeyboardFunc ("keyboard");
	myUT.glutMainLoop ();
    }

    /* Main Loop */
    static public void main (String args[]) throws IOException {
	Frame mainFrame = new Frame ();
	mainFrame.setSize (208, 227);
	select mainCanvas = new select ();
	mainCanvas.init();
	mainFrame.add (mainCanvas);
	mainFrame.setVisible (true);
    }

}