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  1. #1
    Registered User
    Join Date
    Apr 2005
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    2

    bug in OpenGL ES glRotatex ?

    It seems that rotations around vectors
    (1, 0, 0) and (-1, 0, 0) at the some angle are equal (at least visualy) instead of supplemnt each other to 360 degrees. does someone experinced the same problem?

    I am new in Symbian and OpenGL so may
    be it's just my misunderstanding of what glRoate does?

    Can anyoune help?

    I am using SDK S60 2nd fp2
    Last edited by rsalmin; 2005-04-14 at 16:24.

  2. #2
    Nokia Developer Expert
    Join Date
    Mar 2003
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    68
    The reason why they are equivalent is that the rotation vector is the same vector.

    Vectors (1,0,0) ; (-1000,0,0) ; (0.001,0,0) all translate to same normalized vector but with different scale (negative or positive).

    Jani Vaarala
    Graphics Architect
    Nokia
    Last edited by Flame; 2005-04-15 at 09:51.

  3. #3
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    Apr 2005
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    2
    but the rotation around vector (-1, -1, 0) not the same as rotation around (1, 1, 0)
    the sign is significant! when you inverse vector the direction of rotation is also changed. It seems this isn't happen only for vectors with only one non zero coordiante.

  4. #4
    Nokia Developer Expert
    Join Date
    Mar 2003
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    68
    Actually you are right (I just had a look at the GL spec). I forward this to our OpenGL ES implementation team to check.

    Jani Vaarala
    Graphics Architect
    Nokia

  5. #5
    Nokia Developer Expert
    Join Date
    Mar 2003
    Posts
    68
    OK. This is actually a bug in the implementation. Good thing about it is that
    It only affects to axis-aligned rotation vectors (also the reason why it wasn't picked up earlier).

    Thanks for the info.

    Jani Vaarala
    Graphics Architect
    Nokia

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