Posted by moeabdol on Nov 01, 2012; 11:14am
URL: https://forum.jogamp.org/How-to-MultiThread-in-JOGL-tp4026697.html

Dear All,
I have been trying so hard to wrap my head around the multithreading concept in JOGL. I looked into many documentations and it seems to me that every documentation I go through passes me to a next one without me finding a complete and simple code that implements multithreaded rendering.

The program that i'm trying ti implement is simple. Within the class that implement GLEventListener and inside the display() method I have a simple algorithm which is a for loop. Inside the loop am generating random x and y coordinates. What I want to do is draw these points as they are being determined by the random generator to give the viewer a sense of how the points are generated in real-time.

To solve this, I have read documentations on JOGL's website that suggested using GLWindow instead of a JFrame to enable  concurrency. I did that! Moreover, I have created a work class that implements a GLRunnable this class includes all the code necessary to do the work of drawing each point following is the content of this class

  1 import javax.media.opengl.GLRunnable;
  2 import javax.media.opengl.GLAutoDrawable;
  3 import javax.media.opengl.GL2;
  4
  5 public class GLWork implements GLRunnable{
  6         private float x;
  7         private float y;
  8         private boolean in;
  9
 10         GLWork(){
 11                 x = 0.0f;
 12                 y = 0.0f;
 13                 in = false;
 14         }
 15
 16         GLWork(float x, float y, boolean in){
 17                 this.x = x;
 18                 this.y = y;
 19                 this.in = in;
 20         }
 21
 22         @Override
 23         public boolean run(GLAutoDrawable drawable){
 24                 GL2 gl = drawable.getGL().getGL2();
 25
 26                 gl.glPointSize(10.0f);
 27                 gl.glPushMatrix();
 28                 gl.glBegin(GL2.GL_POINTS);
 29                         if(in)
 30                                 gl.glColor3f(1.0f, 0.0f, 0.0f);
 31                         else
 32                                 gl.glColor3f(0.0f, 0.0f, 1.0f);
 33                         gl.glVertex3f(x, y, 0.0f);
 34                 gl.glEnd();
 35                 gl.glPopMatrix();
 36
 37                 return true;
 38         }
 39 }

Following I created another work class that implements Runnable and has a private variable of type GLWork. following is the code

1 import javax.media.opengl.GLAutoDrawable;
  2 import javax.media.opengl.GLRunnable;
  3
  4 public class PointWork implements Runnable{
  5         private GLAutoDrawable drawable;
  6         private GLRunnable runnable;
  7
  8         PointWork(){
  9         }
 10
 11         PointWork(float x, float y, boolean in, GLAutoDrawable drawable){
 12                 this.drawable = drawable;
 13                 this. runnable = new GLWork(x, y, in);
 14         }
 15
 16         public void run(){
 17                 synchronized(drawable){
 18                         drawable.invoke(true, runnable);
 19                 }
 20         }
 21 }

Note that I have synchronized the GLAutoDrawable so no other thread can draw on the drawable while this thread is. I'm not really sure if this is the correct way to do it or not.

Now, for the simple algorithm that does the creation of each point and instantiating threads to draw the point. This is inside the display() method.

57                         float x;                                        // x coordinate
 58                         float y;                                        // y coordinate
 59                         boolean in;                                     // true if point is inside circle
 60                         int inCount = 0;                                // counter for points that are in
 61                         float pi;                                       // estimated pi value
 62                         int totalPoints = 1000;                         // total number of random points
 63                         Random floatRandomGenerator = new Random();     // random number generator
 64                         for(int i = 0; i < totalPoints; i++){
 65                                 x = floatRandomGenerator.nextFloat();
 66                                 y = floatRandomGenerator.nextFloat();
 67                                 if((Math.pow(x - 0.5, 2) + Math.pow(y - 0.5, 2)) <= Math.pow(RADIUS, 2)){
 68                                         in = true;
 69                                         inCount++;
 70                                 }
 71                                 else
 72                                         in = false;
 73                                 new Thread(new PointWork(x, y, in, drawable)).start();
 74                         }

The in variable is just to determine if I should draw the point in red or blue.

I hope that my explanation and code is easy to follow and understand, and I hope that someone out there can help me with this issue. Once I understand how to multithread in JOGL I will be able to do many awesome stuff :) thank you