CylinderGeometryWireframeFriendly function

GeometryBuilder CylinderGeometryWireframeFriendly(double radTop, double radBot, double height, int radialSubdivisions)

Like CylinderGeometry but with duplicate Vertices to make it possible to add aCenter attributes with GenerateWireframeCenters()

Implementation

GeometryBuilder CylinderGeometryWireframeFriendly(
    double radTop, double radBot, double height, int radialSubdivisions) {
  // Compute points on edges
  final double halfHeight = height / 2;
  List<VM.Vector3> top = [];
  List<VM.Vector3> bot = [];
  for (int i = 0; i < radialSubdivisions; i++) {
    double u = i / radialSubdivisions * Math.pi * 2.0;
    double x = Math.sin(u);
    double z = Math.cos(u);
    top.add(VM.Vector3(radTop * x, halfHeight, radTop * z));
    bot.add(VM.Vector3(radBot * x, -halfHeight, radBot * z));
  }
  // repeat three first point so we can safely index with +1
  top.add(top[0]);
  bot.add(bot[0]);
  assert(top.length == radialSubdivisions + 1);
  assert(bot.length == radialSubdivisions + 1);

  final VM.Vector2 zero = VM.Vector2(0.0, 0.0);
  final VM.Vector3 centerTop = VM.Vector3(0.0, halfHeight, 0.0);
  final VM.Vector3 centerBot = VM.Vector3(0.0, -halfHeight, 0.0);

  GeometryBuilder gb = GeometryBuilder();
  gb.EnableAttribute(aTexUV);

  // Q: Why do we have to repeat the vertices?
  // A: Without it example wireframe does not work
  // top and bottom are Face3
  gb.AddFaces3(2 * radialSubdivisions);
  for (int i = 0; i < radialSubdivisions; i++) {
    gb.AddVertices([centerTop, top[i], top[i + 1]]);
    gb.AddVertices([centerBot, bot[i + 1], bot[i]]);
    // TODO: fix these:
    gb.AddAttributesVector2(aTexUV, [zero, zero, zero]);
    gb.AddAttributesVector2(aTexUV, [zero, zero, zero]);
  }

  gb.AddFaces4(radialSubdivisions);
  for (int i = 0; i < radialSubdivisions; i++) {
    gb.AddVertices([top[i + 1], top[i], bot[i], bot[i + 1]]);
    // TODO: fix these:
    gb.AddAttributesVector2(aTexUV, [zero, zero, zero, zero]);
  }
  return gb;
}