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Thread: have problem to calc normal to surface

  1. #1
    Newbie Newbie
    Join Date
    Apr 2013

    have problem to calc normal to surface

    i use a guide in this site that explain how to calc normalized normal
    i try to do that in my project and it not showing the light correctly

    glVertex3d( -3, -3, 0);//v1
    glVertex3d( -3, 3, 0);//v2
    glVertex3d (3, 3, 0);//i did'nt use this vertex only the three other
    glVertex3d (3, -3, 0);//v3

    in the and i get that the normalized normal = (0,0,1.002322884)

  2. #2
    Senior Member OpenGL Guru
    Join Date
    Jun 2013
    The calculated normal is correct (other than some minor rounding error; it should be (0,0,1)) for a clockwise face. For a counter-clockwise face, it should be (0,0,-1). Reversing the order of the vertices will invert the normal.

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