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Thread: My rotations is not correct.

  1. #1
    Junior Member Newbie
    Join Date
    Mar 2001
    Location
    Sweden
    Posts
    8

    My rotations is not correct.

    Hi.
    I have tried to do some scene lately where I want to rotate my object around it self and after that translate it to an arbitrary point in space. After that I want to use gluLookAt... But when I do this I get my object to rotate around itself but then after the gluLookAt it continue to rotate but now in reference to its new point in space. How do I solve this?
    Here is my code:

    glLoadIdentity();
    gluLookAt(-wld->cam->posx,-wld->cam->posy,-wld->cam->posz,wld->cam->lx,wld->cam->ly,wld->cam->lz,0,1,0);

    glRotatef(obj->xv, 1.0f, 0.0f, 0.0f);
    glRotatef(obj->zv, 0.0f, 1.0f, 0.0f);
    glRotatef(obj->yv, 0.0f, 0.0f, 1.0f);
    glTranslatef(float(obj->xp),float(obj->yp),float(obj->zp));

    I have tried to put the gluLookAt after the rotations and the translations but then it disappears from the screen.
    What am I doing wrong?

    /Dew

  2. #2
    Member Newbie
    Join Date
    Oct 2000
    Location
    Toronto, Ontario, Canada
    Posts
    33

    Re: My rotations is not correct.

    If i understand correctly in order to make the object rotate about itself at an arbitrary point in space you should do this

    glLoadIdentity()
    glGluLookAt(...);
    glTranslatef(...);
    glRotatef(xAngle, 1.0, 0.0, 0.0);
    glRotatef(yAngle, 0.0, 1.0, 0.0);
    glRotatef(zAngle, 0.0, 0.0, 1.0);
    draw(...);

    BTW, check your second rotate as it uses the z-angle to rotate about the y-axis.

  3. #3
    Senior Member Regular Contributor
    Join Date
    Feb 2001
    Location
    Australia
    Posts
    431

    Re: My rotations is not correct.

    One other thing to be aware of: if you perform your rotations around the x, y and z axes in order like that, you could come across everyone's favourite topic "gimbal lock". I won't go into it here - it's been covered many times already. Do a search of the discussion boards for "gimbal lock" and "quaternions" and you'll find heaps of links.

    Cheers.

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