# gluLookAt

Gidday! I am trying to move the lookAt part of gluLookat around a sphere centered on the camera. I.E By left clicking I can move my lookAt point ( like left click in WoW ).

I am a little confused about how I calculate the new positions of the lookAt point after my rotations.

Lets say my EyeXYZ = (0,0,4) so 4 back from the scene. and my current lookat point is the origin.

Now lets say I rotate my LookAt point about the camera, 45 degrees on the Y axis, and 30 on the X axis. How do i calculate the new lookAtpoint whilst ensuring its distance from the camera is always the same.

Much appreaciation 2 any replies. Thankyou.   Beware this is z-up (from wikipedia)

phi and theta are your x and y angles

Purespider> If I am not mistaken, these coordinates are cartesian coordinates of the new target position in the camera space (before rotations) which is not necessarly aligned with the world space.
So, I think that FreshFacedNewbie need then to transform these coordinates back in world space to be usable in the gluLookAt function.

You may use it as cam’s position or its lookat, not changing the position at all.
If you want to have a spherical lookat “area” that calcs would just be fine.

Thanks for the replies. I’m checking out some sample code atm, will post back with a small amount of code rather than an open question.

Ok I’ve found some very cool code, most of which I understand. This has rotation on the y axis, (no up and down).

Anyone able to explain how the middle block figures out the new values?

``````
xLookDirection *= l; //the old normalised lookat vector
yLookDirection *= l;
zLookDirection *= l;

//only ySpeed is set to 1. Both xSpeed & zSpeed = 0
//This is because we are only rotating on the y axis.

//Don't understand this block
xNewLookDirection = (CosineAngle + (1 - CosineAngle) * xSpeed) * xLookDirection;
xNewLookDirection += ((1 - CosineAngle) * xSpeed * ySpeed - zSpeed * SineAngle)* yLookDirection;
xNewLookDirection += ((1 - CosineAngle) * xSpeed * zSpeed + ySpeed * SineAngle) * zLookDirection;
zNewLookDirection = ((1 - CosineAngle) * xSpeed * zSpeed - ySpeed * SineAngle) * xLookDirection;
zNewLookDirection += ((1 - CosineAngle) * ySpeed * zSpeed + xSpeed * SineAngle) * yLookDirection;
zNewLookDirection += (CosineAngle + (1 - CosineAngle) * zSpeed) * zLookDirection;

//add new direction vector with length, to camera position to get new lookatpoint.

xView = xPos + xNewLookDirection;
zView = zPos + zNewLookDirection;

``````