MeshGeneratorCylinder.h

#pragma once
 
#include "MeshGeneratorCommon.h"
 
namespace
{
  void cylinderFactory(Mesh * m, const ShapeDefinition & definition, int kRefinementLevels, int kMaxSamples)
  {
    int n = samplesFromLevel(definition.refinement, kRefinementLevels, kMaxSamples) + 3; // +2 is minimum (one triangle at end), but looks bad.
 
    //Uses X dimension for radius, Z for height. Ignores Y
    auto & r = definition.size.x;
    auto & h = definition.size.z;
 
    // End-cap duplication of center vertex, one per triangle in the
    // triangle fan, to reduce texture coordinate twirl-distortion.
    std::vector<PositionNormalTexVertex> V(2 * n + 4 * (n + 1));
    for (int i = 0; i < n; i++) {
      float u = (i + 0.5f) / float(n);
      V[i] = PositionNormalTexVertex({ glm::vec3(0.f, 0.f, -h), glm::vec3(0.f, 0.f, -1.f), glm::vec2(u, 0.f) });
      V[n + 4 * (n + 1) + i] = PositionNormalTexVertex({ glm::vec3(0.f, 0.f, h), glm::vec3(0.f, 0.f, 1.f), glm::vec2(u, 1.f) });
    }
 
    // Cylinder vertices, duplicated along seam. Two set of vertices
    // at each end, one with normals for cylinder body, and one with
    // normals for the caps.
    for (int i = 0; i <= n; i++) {
      float u = float(i) / float(n);
      float cu = r * std::cos(glm::pi<float>() * 2.0f * u);
      float su = r * std::sin(glm::pi<float>() * 2.0f * u);
      V[n + 0 * (n + 1) + i] = PositionNormalTexVertex({ glm::vec3(su, cu, -h), glm::vec3(0.f, 0.f, -1.f), glm::vec2(u, 0.f) });
      V[n + 1 * (n + 1) + i] = PositionNormalTexVertex({ glm::vec3(su, cu, -h), glm::vec3(su, cu, 0.f), glm::vec2(u, 0.f) });
      V[n + 2 * (n + 1) + i] = PositionNormalTexVertex({ glm::vec3(su, cu,  h), glm::vec3(su, cu, 0.f), glm::vec2(u, 1.f) });
      V[n + 3 * (n + 1) + i] = PositionNormalTexVertex({ glm::vec3(su, cu,  h), glm::vec3(0.f, 0.f, 1.f), glm::vec2(u, 1.f) });
    }
 
    std::vector<uint32_t> I;
    I.reserve(3 * 4 * n);
    for (int i = 0; i < n; i++) { // start cap
      I.push_back(i);
      I.push_back(n + i);
      I.push_back(n + i + 1);
    }
 
    for (int i = 0; i < n; i++) { // body
      I.push_back(n + 1 * (n + 1) + i);
      I.push_back(n + 2 * (n + 1) + i);
      I.push_back(n + 1 * (n + 1) + i + 1);
 
      I.push_back(n + 1 * (n + 1) + i + 1);
      I.push_back(n + 2 * (n + 1) + i);
      I.push_back(n + 2 * (n + 1) + i + 1);
    }
 
    for (int i = 0; i < n; i++) { // end cap
      I.push_back(n + 3 * (n + 1) + i + 1);
      I.push_back(n + 3 * (n + 1) + i);
      I.push_back(n + 4 * (n + 1) + i);
    }
 
    m->setVertexData(V.data(), V.size());
    m->setIndexData(I.data(), I.size());
    m->setBounds(computeBoundingBoxFromVertexFormat(V.begin(), V.end()));
  }
}