plane.cpp

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/*
 * plane.cpp
 *
 * Copyright (C) 2010  Thomas A. Vaughan
 * All rights reserved.
 *
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the <organization> nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THOMAS A. VAUGHAN ''AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THOMAS A. VAUGHAN BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 *
 * Geometry methods specific to 3D planes (2D planes in 3D space)
 */

// includes --------------------------------------------------------------------
#include "plane.h"              // always include our own header first


static const float s_eps                = 1.0e-6;


////////////////////////////////////////////////////////////////////////////////
//
//      static helper methods
//
////////////////////////////////////////////////////////////////////////////////


////////////////////////////////////////////////////////////////////////////////
//
//      public API
//
////////////////////////////////////////////////////////////////////////////////

bool
getLineOfIntersection
(
IN const plane_t& A,
IN const plane_t& B,
OUT point3d_t& p0,
OUT point3d_t& pt
)
throw()
{
        // intersection line direction is cross product of two plane normals
        pt = crossProduct(A.n, B.n);
        float n2 = dotProduct(pt, pt);
        if (n2 < s_eps) {
                DPRINTF("length of cross product: %f", n2);
                return false;   // cross product is zero--no intersection
        }
        normalize(pt);

        // now we need to find p0, a point on the intersection line
        float ab = dotProduct(A.n, B.n);
        float ab2 = ab * ab;
        float denom = 1.0 - ab2;
        if (denom < s_eps) {
                DPRINTF("1 - ab2 = %f", denom);
                // normals are nearly coincident
                return false;
        }

        float b = (B.d - A.d * ab) / denom;
        float a = A.d - b * ab;

        p0 = a * A.n + b * B.n;
        return true;
}