rotate an object in Opengl

This is a discussion on rotate an object in Opengl within the Game Programming forums, part of the General Programming Boards category; Hi, i'm learning opengl through a little app and now ive bumped into the 3d rotational problem. I store data ...

  1. #1
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    rotate an object in Opengl

    Hi, i'm learning opengl through a little app and now ive bumped into the 3d rotational problem.

    I store data for my object both the Rotation matrix and the quaternion. I want to visualize it and i tried to use glrotatef() with a quaternion_toAxisAngle() function but it doesnt quite work since glrotatef() accepts angles from 0 to 360 degrees and my quaternion_toAxisAngle() delivers an angle between -180 and 180 so when it starts to rotate around the x axis it does well between 0 and 180 degrees but then it stops rotating and gets stuck at 180 degrees. This happens when i apply a torque in the x axis.

    I think i cannot modify my quaternion_toAxisAngle() function to match the angle requirements so what are the alternatives?
    How can i do in order to have the object rotating 360 degrees?


    thanks in advance from Spain!!

  2. #2
    Super Moderator VirtualAce's Avatar
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    -180 to 180 is 360 degrees. The function is using values relative to PI instead of 2 * PI. I don't see the problem.

  3. #3
    C++11 User Tux0r's Avatar
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    You um don't actually rotate objects in OpenGL you rotate your projection matrix...

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    -180 to 180 is 360 degrees. The function is using values relative to PI instead of 2 * PI. I don't see the problem.
    the rotation must be 360 degrees clockwise o counterclockwise, not just only 180

  5. #5
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    You um don't actually rotate objects in OpenGL you rotate your projection matrix...
    I thought the vertex data was modified by the model view matrix?

    To the question: Why not write a converter which maps 0..180 to the corresponding value and -180..-1 to 180..359? But I think this is unneccessary.

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    Ok, solved!!, the strange rotation i was having made me think there was somthing with the angles range but there wasn't.

    The error was i was rotating a vector by a quaternion when what i really wanted was to perform a multiplication between a quaternion and another quaternion from a vector:

    v2 = Q *v*Q'

    instead of

    Q2 = Q * Qv where Qv is (0, vx, vy, vz)

    (this happens when we use math libraries we arent familiar with!!)


    thanks for your responses

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