arcball.cpp

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/*
    Sheep - A Rigid Body Dynamics Engine
    Copyright (C) 2001-2004 Francois Beaune
    Contact: http://toxicengine.sourceforge.net/

    This file is part of Sheep.

    Sheep is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    Sheep is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with Sheep; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

#include "arcball.h"    // include first
#include "common/math/real.h"

#include <cmath>

using namespace sheep;

Vector3 Arcball::point_on_sphere(const Vector2 &p) const {
    Vector3 p1;

    p1.m_x = p.m_x;
    p1.m_y = p.m_y;

    Real m = sq(p.m_x) + sq(p.m_y);

    if(m < 1.0)
        // Point (x, y) is above the unit sphere.
        p1.m_z = sqrt(1.0 - m);
    else {
        // If the point does not lie on the sphere, push it back
        // to the sphere border.
        m = sqrt(m);
        p1.m_x /= m;
        p1.m_y /= m;
        p1.m_z = 0.0;
    }

    assert(feq(p1.Norm(), 1.0));

    return p1;
}

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