Here is a great example of what I would like to do:

http://www.vizmo.com/rgizmo.html

Will do Egon.  Thanks!

Hi Egon,

Thanks for the code!  I tried messaging you before but I think my browser was acting up.. the replies never end up in the outbox. :-S

Your example seems to be similar to my Euler Angle Rotation example here:

http://testcod07.fortunecity.com/rotate/EulerRotateCamTest/

It's not really what I'm trying to accomplish. I'm trying to get the same effect that google earth has.  The use clicks on the screen, the code calculates the closet point on an imaginary sphere as the drag point. As the user drags the cursor around the screen, the camera moves such that the original point grabbed is rotated to where the current mouse position is.  If the user drags outside the sphere area and around it would rotate around the Z axis (i believe).

Does that make sense?   I think the term is called Trackball Rotation? or Virtual Trackball Rotation.


Very grateful for your time.

Storm.

Hi again,

I'm trying to figure out how to rotate an object relative to the X Y axis of the screen space.

This *seemed* at first to almost work, but when I move the camera behind or under the object, I get inverse and / or reverse rotations - so I guess I'm way off here. :-(

Any suggestions?

Thank you,

S.

public SimpleVector rotateRespect2Cam(float rotX, float rotY)
{
   SimpleVector dir = theCamera.getDirection();

   dir.rotateX(rotX);
   dir.rotateY(rotY);

   return dir.calcSub(theCamera.getDirection());
}

SimpleVector rotate = rotateRespect2Cam(delta.x * -camRotSpeed, delta.y * -camRotSpeed);

object.rotateX(rotate.x);  // rx rz ry to avoid gimbal lock.
object.rotateZ(rotate.z);
object.rotateY(rotate.y);


A tutorial would be good! Can't we wiki it somehow? Then we could all help out...

A wiki would be great.

EDIT: This, of course, does not depend on the user actually grabbing the sphere. If that's an issue then you could use Interact2D to check if the user is actually clicking on the sphere or not, and then calculating the distance from that point to the center of the sphere (instead of calculating the distance from the click and to the center of the screen).

The sphere is imaginary.     Basically I have a 3D graph chart as a scene and I wanted to implement "natural rotations" around the chart (scene).  The effect is that if the user grabs a point and drags it in any zig zag direction, they can return to the scene to the original view by simply dragging the mouse back to its original mouse down position -  "zero-hysteresis rotation".  With normal rotations you cant really do this. :-S  Also, the original mouse-down point can not be rotated behind the sphere.

I believe this sort of explains it better:
http://www.mactech.com/articles/mactech/Vol.15/15.03/NaturalObjectRotation/index.html

The main idea is to think in terms of arc intervals. If we have two arbitrary points A and B on the surface of a unit sphere, the most natural way to get from A to B is to rotate the sphere so that A follows the shortest path (or geodesic) from A to B. Thus the rotation occurs in the plane of the geodesic. If a = (xa, ya, za) and b = (xb,yb,zb) are the position vectors of the points, the axis of rotation is given by a 5 b. The angle of the rotation can be obtained from cos-1 (a × b).

How do we get from 2D mouse coordinates to 3D rotations? We construct a pseudo-3D coordinate space as follows. (This is essentially the method of Shoemake in Graphic Gems IV, p. 176.) Superimpose an imaginary sphere on our 3D object such that the center of the sphere is at the position vector c = (screen_x, screen_y, 0), where screen_x and screen_y are the local screen coordinates of the center of the object. We assume that any mouse-downs will happen on the surface of our imaginary sphere, which has a radius of r pixels.

I'd prefer to rotate the camera rather than the scene ^_^  To be honest my math is rusty to achieve this :-(

I'd love this feature too :-D

Hi,

Still working on my grid lines.   

project3D2D wont render if "the center is behind the viewplane".   How can I adjust my vectors to clip at the approriate end?

Much thanks.

S.

   
    private void drawLine(FrameBuffer fb, Graphics2D g, SimpleVector v1, SimpleVector v2)
    {
        SimpleVector point1 = Interact2D.project3D2D(theWorld.getCamera(), fb, v1);
        SimpleVector point2 = Interact2D.project3D2D(theWorld.getCamera(), fb, v2);


        if(point1 != null && point2 != null)
        {
            g.drawLine((int)point1.x, (int)point1.y, (int)point2.x, (int)point2.y);
        }  // if
    }