View Full Version : Model Translations

03-13-2007, 01:31 PM
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() {
// 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

}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

03-14-2007, 07:59 AM
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.

03-14-2007, 08:59 AM
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.


03-15-2007, 06:04 AM
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.