Cube.hpp

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#pragma once
 
#include <array>
#include <cstdint>
#include <glm/geometric.hpp>
#include <glm/vec3.hpp>
 
namespace sKit {
 
struct Cube {
  Cube() = default;
  Cube(float size) : size(size) {
    std::array<glm::vec3, 8> base;
    auto p = size * 0.5;
    base[0] = {-p, -p, p};
    base[1] = {p, -p, p};
    base[2] = {p, -p, -p};
    base[3] = {-p, -p, -p};
    base[4] = {-p, p, p};
    base[5] = {p, p, p};
    base[6] = {p, p, -p};
    base[7] = {-p, p, -p};
 
    // Face 1
    vertices[0] = base[0];
    vertices[1] = base[4];
    vertices[2] = base[5];
    vertices[3] = base[1];
    // Face 2
    vertices[4] = base[1];
    vertices[5] = base[5];
    vertices[6] = base[6];
    vertices[7] = base[2];
    // Face 3
    vertices[8] = base[2];
    vertices[9] = base[6];
    vertices[10] = base[7];
    vertices[11] = base[3];
    // Face 4
    vertices[12] = base[3];
    vertices[13] = base[7];
    vertices[14] = base[4];
    vertices[15] = base[0];
    // Face 5
    vertices[16] = base[4];
    vertices[17] = base[7];
    vertices[18] = base[6];
    vertices[19] = base[5];
    // Face 6
    vertices[20] = base[3];
    vertices[21] = base[0];
    vertices[22] = base[1];
    vertices[23] = base[2];
 
    // Face 1 - Tri 1 - 2
    indices[0] = 0;
    indices[1] = 1;
    indices[2] = 2;
    indices[3] = 0;
    indices[4] = 2;
    indices[5] = 3;
    // Face 2 - Tri 3 - 4
    indices[6] = 4;
    indices[7] = 5;
    indices[8] = 6;
    indices[9] = 4;
    indices[10] = 6;
    indices[11] = 7;
    // Face 3 - Tri 5 - 6
    indices[12] = 8;
    indices[13] = 9;
    indices[14] = 10;
    indices[15] = 8;
    indices[16] = 10;
    indices[17] = 11;
    // Face 4 - Tri 7 - 8
    indices[18] = 12;
    indices[19] = 13;
    indices[20] = 14;
    indices[21] = 12;
    indices[22] = 14;
    indices[23] = 15;
    // Face 5 - Tri 9 - 10
    indices[24] = 16;
    indices[25] = 17;
    indices[26] = 18;
    indices[27] = 16;
    indices[28] = 18;
    indices[29] = 19;
    // Face 6 - Tri 11 - 12
    indices[30] = 20;
    indices[31] = 21;
    indices[32] = 22;
    indices[33] = 20;
    indices[34] = 22;
    indices[35] = 23;
 
    for (size_t i = 0; i < vertices.size(); ++i) {
      v[i * 3] = vertices[i].x;
      v[i * 3 + 1] = vertices[i].y;
      v[i * 3 + 2] = vertices[i].z;
    }
    for (size_t i = 0; i < 12; i++) {
      size_t ia = i * 3;
      size_t ib = i * 3 + 1;
      size_t ic = i * 3 + 2;
      auto a = vertices[indices[ia]];
      auto b = vertices[indices[ib]];
      auto c = vertices[indices[ic]];
      auto normal = glm::normalize(glm::cross(b - a, c - a));
      normals[indices[ia]] = normal;
      normals[indices[ib]] = normal;
      normals[indices[ic]] = normal;
    }
 
    for (size_t i = 0; i < normals.size(); ++i) {
      n[i * 3] = normals[i].x;
      n[i * 3 + 1] = normals[i].y;
      n[i * 3 + 2] = normals[i].z;
    }
  };
 
  std::array<glm::vec3, 24> vertices;
  std::array<float, 72> v;
  std::array<uint16_t, 36> indices;
  std::array<glm::vec3, 24> normals;
  std::array<float, 72> n;
  float size;
};
 
}  // namespace sKit