visibility.h

/*****************************************************************************
 * VCLib                                                                     *
 * Visual Computing Library                                                  *
 *                                                                           *
 * Copyright(C) 2021-2025                                                    *
 * Visual Computing Lab                                                      *
 * ISTI - Italian National Research Council                                  *
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 * This program is free software; you can redistribute it and/or modify      *
 * it under the terms of the Mozilla Public License Version 2.0 as published *
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 * (at your option) any later version.                                       *
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 * This program 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              *
 * Mozilla Public License Version 2.0                                        *
 * (https://www.mozilla.org/en-US/MPL/2.0/) for more details.                *
 ****************************************************************************/
 
#ifndef VCL_MESH_ELEM_ALGORITHMS_VISIBILITY_H
#define VCL_MESH_ELEM_ALGORITHMS_VISIBILITY_H
 
#include <vclib/mesh/elements.h>
 
#include <vclib/algorithms/core.h>
 
namespace vcl {
 
template<FaceConcept FaceType, Point3Concept PointType>
auto halfSpaceDeterminant(const FaceType& face, const PointType& point)
{
    // - if it is a triangle, compute the determinant using the triangle
    // - if it is a polygon, use its normal to compute the determinant
    if constexpr (TriangleFaceConcept<FaceType>) {
        return halfSpaceDeterminant(
            face.vertex(0)->position(),
            face.vertex(1)->position(),
            face.vertex(2)->position(),
            point);
    }
    else {
        if (face.vertexNumber() == 3) {
            return halfSpaceDeterminant(
                face.vertex(0)->position(),
                face.vertex(1)->position(),
                face.vertex(2)->position(),
                point);
        }
        else {
            PointType n = faceNormal(face);
            return n.dot(point - face.vertex(0)->position());
        }
    }
}
 
template<FaceConcept FaceType, Point3Concept PointType>
bool facePointVisibility(const FaceType& face, const PointType& point)
{
    return halfSpaceDeterminant(face, point) > 0;
}
 
} // namespace vcl
 
#endif // VCL_MESH_ELEM_ALGORITHMS_VISIBILITY_H