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This program demonstrates use of OpenGL feedback. First, a lighting environment is set up and a few lines are drawn. Then feedback mode is entered, and the same lines are drawn. The results in the feedback buffer are printed.
The example is ported from C examples in the OpenGL Programming Guide (known as the "red book").
-> Copyright and Permission Notice
package glredbook10;
import javax.swing.*;
import java.awt.event.*;
import java.nio.*;
import javax.media.opengl.*;
import javax.media.opengl.glu.*;
import com.sun.opengl.util.*;
/**
* This program demonstrates use of OpenGL feedback. First, a lighting
* environment is set up and a few lines are drawn. Then feedback mode is
* entered, and the same lines are drawn. The results in the feedback buffer are
* printed.
*
* @author Kiet Le (Java conversion)
*/
public class feedback
extends JFrame
implements GLEventListener, KeyListener
{
private GLCapabilities caps;
private GLCanvas canvas;
private FPSAnimator animator;
private GLU glu;
private GLUT glut;
public feedback()
{
super("feedback");
canvas = new GLCanvas();
canvas.addGLEventListener(this);
canvas.addKeyListener(this);
getContentPane().add(canvas);
}
public void run()
{
setSize(200, 200);
setLocationRelativeTo(null);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setVisible(true);
canvas.requestFocusInWindow();
}
public static void main(String[] args)
{
new feedback().run();
}
public void init(GLAutoDrawable drawable)
{
GL gl = drawable.getGL();
glu = new GLU();
glut = new GLUT();
gl.glEnable(GL.GL_LIGHTING);
gl.glEnable(GL.GL_LIGHT0);
}
public void display(GLAutoDrawable drawable)
{
GL gl = drawable.getGL();
float feedBuffer[] = new float[1024];
FloatBuffer feedBuf = BufferUtil.newFloatBuffer(1024);
int size;
gl.glMatrixMode(GL.GL_PROJECTION);
gl.glLoadIdentity();
gl.glOrtho(0.0, 100.0, 0.0, 100.0, 0.0, 1.0);
gl.glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
gl.glClear(GL.GL_COLOR_BUFFER_BIT);
drawGeometry(gl, GL.GL_RENDER);
gl.glFeedbackBuffer(1024, GL.GL_3D_COLOR, feedBuf);
gl.glRenderMode(GL.GL_FEEDBACK);
drawGeometry(gl, GL.GL_FEEDBACK);
size = gl.glRenderMode(GL.GL_RENDER);
feedBuf.get(feedBuffer);
printBuffer(gl, size, feedBuffer);
}
public void reshape(GLAutoDrawable drawable, int x, int y, int width,
int height)
{
}
public void displayChanged(GLAutoDrawable drawable, boolean modeChanged,
boolean deviceChanged)
{
}
/*
* Draw a few lines and two points, one of which will be clipped. If in
* feedback mode, a passthrough token is issued between the each primitive.
*/
void drawGeometry(GL gl, int mode)
{
gl.glBegin(GL.GL_LINE_STRIP);
gl.glNormal3f(0.0f, 0.0f, 1.0f);
gl.glVertex3f(30.0f, 30.0f, 0.0f);
gl.glVertex3f(50.0f, 60.0f, 0.0f);
gl.glVertex3f(70.0f, 40.0f, 0.0f);
gl.glEnd();
if (mode == GL.GL_FEEDBACK) gl.glPassThrough(1.0f);
gl.glBegin(GL.GL_POINTS);
gl.glVertex3f(-100.0f, -100.0f, -100.0f); /* will be clipped */
gl.glEnd();
if (mode == GL.GL_FEEDBACK) gl.glPassThrough(2.0f);
gl.glBegin(GL.GL_POINTS);
gl.glNormal3f(0.0f, 0.0f, 1.0f);
gl.glVertex3f(50.0f, 50.0f, 0.0f);
gl.glEnd();
}
/* Write contents of one vertex to stdout. */
void print3DcolorVertex(int size, int count, float[] buffer)
{
int i;
System.out.println(" ");
for (i = 0; i < 7; i++)
{
System.out.println(" "+ buffer[size - count]);
count = count - 1;
}
System.out.println();
}
/* Write contents of entire buffer. (Parse tokens!) */
private void printBuffer(GL gl, int size, float[] buffer)
{
int count;
float token;
count = size;
while (count > 0)
{
token = buffer[size - count];
count--;
if (token == GL.GL_PASS_THROUGH_TOKEN)
{
System.out.println("GL.GL_PASS_THROUGH_TOKEN");
System.out.println("\t " + buffer[size - count]);
count--;
}
else if (token == GL.GL_POINT_TOKEN)
{
System.out.println("GL.GL_POINT_TOKEN");
print3DcolorVertex(size, count, buffer);
}
else if (token == GL.GL_LINE_TOKEN)
{
System.out.println("GL.GL_LINE_TOKEN ");
print3DcolorVertex(size, count, buffer);
print3DcolorVertex(size, count, buffer);
}
else if (token == GL.GL_LINE_RESET_TOKEN)
{
System.out.println("GL.GL_LINE_RESET_TOKEN ");
print3DcolorVertex(size, count, buffer);
print3DcolorVertex(size, count, buffer);
}
}
}
public void keyTyped(KeyEvent key)
{
}
public void keyPressed(KeyEvent key)
{
switch (key.getKeyChar()) {
case KeyEvent.VK_ESCAPE:
System.exit(0);
break;
default:
break;
}
}
public void keyReleased(KeyEvent key)
{
}
}
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Source:
Kiet Le's The Red Book Examples using JOGL
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