using gluUnProject

OpenGL Development JOGL Development
#1

Greetings, once more. I’m trying to use gluUnProject to get world coordinates for my mouse. However the calls to glGetIntegerv, glGetDoublev to get the viewport, modelview and projection matrices return 0 values.
My questions are:
Can I do this inside the Mouse Listener methods:
I still need a gl, glu object. How do I pass these to:
public void mouseClicked(MouseEvent e)

right now I’ve created a helper class:


class TransformMouseCoords {
    GLDrawable glDrawable;
    
    public void initClass(GLDrawable glDrawable) {
      this.glDrawable = glDrawable;
      
    }
    public void makeTransform(int x, int y, double worldX, double worldY) {
      GL gl = glDrawable.getGL();
      GLU glu = glDrawable.getGLU();
      
      int[] viewport = new int[4];
      double[] mvmatrix = new double[16];
      double[] projmatrix = new double[16];
      int realy;
      double[] worldCoords = new double[3];
      /*double[] wy = new double[1];
      double[] wz = new double[1];*/
      
      gl.glGetIntegerv(GL.GL_VIEWPORT, viewport);
      gl.glGetDoublev(GL.GL_MODELVIEW_MATRIX, mvmatrix);
      gl.glGetDoublev(GL.GL_PROJECTION_MATRIX, projmatrix);
      realy = viewport[3] - y  - 1;
      System.out.println("Coordinates at cursor: (" + x + ", " + realy + ")");
      for (int i = 0; i < 4; i++) 
          System.out.println(viewport[i]);
      
      for (int i = 0; i < 16; i++) {
          System.out.println(projmatrix[i]);
      }
      for (int i = 0; i < 16; i++) {
          System.out.println(mvmatrix[i]);
      }
      glu.gluUnProject((double)x, (double)realy, 0.0, 
            mvmatrix, projmatrix, viewport,
            worldCoords);
      worldX = worldCoords[0];
      worldY = worldCoords[1];
      System.out.println("Coordinates at world: (" + worldCoords[0] + ", " + worldCoords[1] + ")");
    }
}

which I call in mouseClicked.


public void mouseClicked(MouseEvent e) {
        int x = e.getX();
        int y = e.getY();
        double worldX = 0, worldY = 0;
        tmc.makeTransform(x, y, worldX, worldY);
        System.out.println("we got coordinates: (" + worldX + ", " + worldY + ")");
    }

Am I missing something in passing variables in Java? Why are my viewport, modelview and projection matrices filled with zeros?
PS. I call initClass inside my display callback, just to be sure I get a valid glDrawable each time. Is this correct?

#2

Bluntly, no.

OpenGL calls are only valid from the thread that the OpenGL context was created from, which is what the GLEventListener display callbacks are attempting to enforce. In general, its a bad idea to maintain a reference to the GL object, instead just keep passing it down as a method arg and you can’t make calls from an invalid thread.

The mouse events come from an AWT event thread, so GL calls won’t be valid. A half-assed solution is to set a flag and queue up calls to gluUnProject etc. and do them later. A more general method that I’ve used is to queue up all your mouse events when they actually happen, and then flush this queue (performing any actual handling logic) during a display callback. This is fairly easy to do with just a simple wrapper around where you add your mouse event listeners to your GL display.