Hex Grid Math

HexMath.cs

using UnityEngine;

public struct HexCoord
{
  public float q;
  public float r;
  public float s;

  public HexCoord(float q, float r)
  {
    this.q = q;
    this.r = r;
    this.s = -q - r;
  }

  public HexCoord(float q, float r, float s)
  {
    this.q = q;
    this.r = r;
    this.s = s;
  }
}

public static class HexMath
{
  public const float kSqrt3 = 1.73205080757f;
  public const float kHexSize = 0.5f;
  public const float kHexWidth = kSqrt3 * kHexSize;
  public const float kHexHeight = 2 * kHexSize;

  public static HexCoord CartesianToHex(Vector3 pos)
  {
    HexCoord hex;
    hex.q = (kSqrt3 / 3f * pos.x - 1f / 3f * pos.z) / kHexSize;
    hex.r = (2f / 3f * pos.z) / kHexSize;
    hex.s = -hex.q - hex.r;

    return hex;
  }

  public static Vector3 HexToCartesian(HexCoord hex)
  {
    Vector3 pos = Vector3.zero;
    pos.x = kHexSize * (kSqrt3 * hex.q + kSqrt3 / 2f * hex.r);
    pos.z = kHexSize * (3f / 2f * hex.r);
    return pos;
  }

  public static HexCoord RoundHex(HexCoord hex)
  {
    HexCoord rounded = new HexCoord(Mathf.Round(hex.q), Mathf.Round(hex.r), Mathf.Round(hex.s));
    HexCoord diff = new HexCoord(Mathf.Abs(rounded.q - hex.q), Mathf.Abs(rounded.r - hex.r), Mathf.Abs(rounded.s - hex.s));

    if (diff.q > diff.r && diff.q > diff.s)
      rounded.q = -rounded.r - rounded.s;
    else if (diff.r > diff.s)
      rounded.r = -rounded.q - rounded.s;
    else
      rounded.s = -rounded.q - rounded.r;

    return rounded;
  }
}