BezierMesh.hpp

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//
//  CeresEngine - A game development framework
//
//  Created by Rogiel Sulzbach.
//  Copyright (c) 2018-2022 Rogiel Sulzbach. All rights reserved.
//
 
#pragma once
 
#include "ParametricMesh.hpp"
 
#include <algorithm>
#include <limits>
 
namespace CeresEngine::MeshGenerator {
 
    template<int D0, int D1> class BezierMesh {
    private:
        static_assert(D0 > 1, "D0 must be > 1.");
        static_assert(D1 > 1, "D1 must be > 1.");
 
        using Impl = ParametricMesh;
        Impl mParametricMesh;
 
        struct ArrayWrapper {
            Vector3 data[D1][D0];
 
            ArrayWrapper(const Vector3 (&p)[D1][D0]) { std::copy(&p[0][0], &p[0][0] + D1 * D0, &data[0][0]); }
        };
 
        explicit BezierMesh(const ArrayWrapper& p, const Vector2i& segments)
                : mParametricMesh{[p](const Vector2& t) {
                                      MeshVertex vertex;
 
                                      vertex.position = bezier2(p.data, t);
 
                                      Matrix2x3 J = bezier2Jacobian<1>(p.data, t);
                                      vertex.normal = cross(J[0], J[1]);
 
                                      // If the normal was zero try a again near by.
                                      const double e = std::numeric_limits<double>::epsilon();
                                      if(dot(vertex.normal, vertex.normal) < e) {
                                          J = bezier2Jacobian<1>(p.data, t + 10.0 * e);
                                          vertex.normal = cross(J[0], J[1]);
                                      }
                                      vertex.normal = normalize(vertex.normal);
 
                                      vertex.texCoord = t;
 
                                      return vertex;
                                  },
                      segments} {}
 
    public:
        explicit BezierMesh(const Vector3 (&p)[D1][D0], const Vector2i& segments = {16, 16})
                : // Work around a msvc lambda capture bug by wrapping the array.
                  BezierMesh{ArrayWrapper{p}, segments} {}
 
        using Triangles = typename Impl::Triangles;
        [[nodiscard]] Triangles triangles() const noexcept { return mParametricMesh.triangles(); }
 
        using Vertices = typename Impl::Vertices;
        [[nodiscard]] Vertices vertices() const noexcept { return mParametricMesh.vertices(); }
    };
 
} // namespace CeresEngine::MeshGenerator