Model Translations

OpenGL OpenGL: Basic Coding
1

Please Help,

I am sure this is a common problem with OpenGL newbies. I am having some difficulty with the glRotatef and glTranslatef functions I hope someone can help me with. I want to allow the user to rotate (with left-mouse button) and move the Model (with right-mouse button). When I comment out either the rotations or translates separately they work fine, but when used together I get basically a rotation with some periodic jittering.

A snippet of my code follows:

public void draw() {
       glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  glPushMatrix();
  // Rotate around the X, Y, and Z axes
  glRotatef(angleX, 1.0f, 0.0f, 0.0f);
  glRotatef(angleY, 0.0f, 1.0f, 0.0f);
  gl.glRotatef(angleZ, 0.0f, 0.0f, 1.0f); 

  // Move the Model
  glTranslatef(xTrans, 0.0f, 0.0f);
  glTranslatef(0.0f, yTrans, 0.0f);
  glTranslatef(0.0f, 0.0f, 1.0f);

  // Draw Model here
  drawCube();

  glPopMatrix(); 
  glFlush();
}

The xTrans, yTrans, angleX, angleY, and angleZ have been previously calculated from coordinates from the mouse. I think the problem may be the order of the Matrix transformations? Can anyone give me some hints as to why this is happening?

Thanks in advance

2

Put glTranslatef first.

And, why you won’t combine 3 of your translates into one: “glTranslatef(xTrans, yTrans, 1.0f)”;?

No clue why you get jittering, though.

3

Thanks for the reply, Gremour.
You’re right, I don’t know why I didn’t just put the glTranslatef into one function. However, I get no translation when I place the glTranslatef. Perhaps the way I am calculating the rotates and translates is not correct. The following is a sample of my code:

// Constructor
  public myClass() {
     mouseRButtonDown = false;
     view_rotx = 20.0f;
     view_roty = 30.0f;
     view_rotz = 0.0f; 
     xTrans = yTrans = 0.0f;
     xTransInit = yTransInit = 0.0f;
  }

  public void mousePressed(MouseEvent e) {
    prevMouseX = e.getX();
    prevMouseY = e.getY();
    if ((e.getModifiers() & e.BUTTON3_MASK) != 0) {
      mouseRButtonDown = true;
      Rectangle bounds = e.getComponent().getBounds();
      xTransInit = ((e.getX()/(float)bounds.getMaxX())*2.0f) - 1.0f;
      yTransInit = ((((float)bounds.getMaxY() - e.getY())/(float) bounds.getMaxY()) * 2.0f) - 1.0f;
    }
  }

  public void mouseReleased(MouseEvent e) {
    if ((e.getModifiers() & e.BUTTON3_MASK) != 0) {
      mouseRButtonDown = false;
   }
  }

  public void mouseDragged(MouseEvent e) {
		int x = e.getX();
    		int y = e.getY();
    		Dimension size = e.getComponent().getSize();

    		float thetaY = 360.0f * ( (float)(x-prevMouseX)/(float)size.width);
    		float thetaX = 360.0f * ( (float)(prevMouseY-y)/(float)size.height);
    
    		prevMouseX = x;
    		prevMouseY = y;

    		view_rotx += thetaX;
    		view_roty += thetaY;


		// Calculate the Change for MouseMovement
		if (mouseRButtonDown) {
			Rectangle bounds = e.getComponent().getBounds();
			
			float xVal = ((e.getX()/(float)bounds.getMaxX())*2.0f) - 1.0f;
			float yVal = ((((float)bounds.getMaxY() - e.getY())/(float)bounds.getMaxY())*2.0f) - 1.0f;

			xTrans -= (xTransInit - xVal);
			yTrans -= (yTransInit - yVal);

			xTransInit = xVal;
			yTransInit = yVal;
		}

	}

I have no idea why the translations are not showing but the rotations are. BTW, I am using Java JOGL but the bindings to OpenGL are basically one-to-one.

Thanks.

4

Does anybody know if the code I have posted has any kind of obvious problem with the way I am calculating the rotations? I am not so sure about the Z-Rotational value.

Thanks.