knot_path.cpp

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#include "knot_path.hpp"
 
using namespace generator;
 
namespace
{
 
gml::dvec3 knot(int p, int q, double t)
{
    t *= gml::radians(360.0);
 
    const double pt = p * t;
    const double qt = q * t;
 
    const double sinpt = std::sin(pt);
    const double cospt = std::cos(pt);
    const double sinqt = std::sin(qt);
    const double cosqt = std::cos(qt);
 
    const double r = 0.5 * (2.0 + sinqt);
 
    return gml::dvec3{r * cospt, r * sinpt, r * cosqt};
}
} // namespace
 
knot_path_t::knot_path_t(int p, int q, int segments)
    : parametric_path_{[p, q](double t)
                       {
                           path_vertex_t vertex;
 
                           vertex.position = knot(p, q, t);
 
                           const gml::dvec3 prev = knot(p, q, t - 0.01);
                           const gml::dvec3 next = knot(p, q, t + 0.01);
 
                           vertex.tangent = normalize(next - prev);
 
                           vertex.normal = normalize(cross(next - prev, next + prev));
 
                           vertex.tex_coord = t;
 
                           return vertex;
                       },
                       segments}
{
}