AppExperiments

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

namespace Leap.Unity.MeshUtilities {

  public enum Face {
    None = 0,
    Back = 1,
    Front = 2,
    All = 3
  }

  public static class CubeBuilder {
    private static List<Vector3> _verts = new List<Vector3>();
    private static List<int> _tris = new List<int>();

    public static void CreateCubeMesh(Mesh mesh,
                                Bounds bounds,
                                Face bottom = Face.None,
                                Face left = Face.None,
                                Face right = Face.None,
                                Face back = Face.None,
                                Face top = Face.None,
                                Face front = Face.None) {
      _verts.Clear();
      _tris.Clear();

      for (int sx = -1; sx <= 1; sx += 2) {
        for (int sy = -1; sy <= 1; sy += 2) {
          for (int sz = -1; sz <= 1; sz += 2) {
            Vector3 delta = bounds.size * 0.5f;
            delta.x *= sx;
            delta.y *= sy;
            delta.z *= sz;

            Vector3 corner = bounds.center + delta;
            _verts.Add(corner);
          }
        }
      }

      {
        addQuad(0, 4, 5, 1, bottom); //bottom
        addQuad(0, 1, 3, 2, left); //left
        addQuad(4, 6, 7, 5, right); //right
        addQuad(1, 5, 7, 3, back); //back
        addQuad(2, 3, 7, 6, top); //top
        addQuad(0, 2, 6, 4, front); //front
      }

      mesh.SetVertices(_verts);
      mesh.SetTriangles(_tris, 0);
      mesh.RecalculateBounds();
    }

    public static void CreateQuadMesh(Mesh mesh, Rect rect, Face face = Face.All) {
      _verts.Clear();
      _tris.Clear();

      _verts.Add(rect.position);
      _verts.Add(rect.position + Vector2.right * rect.width);
      _verts.Add(rect.position + rect.size);
      _verts.Add(rect.position + Vector2.up * rect.height);

      addQuad(0, 1, 2, 3, face);

      mesh.SetVertices(_verts);
      mesh.SetTriangles(_tris, 0);
      mesh.RecalculateBounds();
    }

    private static void addQuad(int a, int b, int c, int d, Face face) {
      if ((face & Face.Front) != 0) {
        _tris.Add(a);
        _tris.Add(b);
        _tris.Add(c);

        _tris.Add(a);
        _tris.Add(c);
        _tris.Add(d);
      }

      if ((face & Face.Back) != 0) {
        _tris.Add(a);
        _tris.Add(c);
        _tris.Add(b);

        _tris.Add(a);
        _tris.Add(d);
        _tris.Add(c);
      }
    }
  }

}