Unity : Hexagonal Grids

I recently started working on a project with a friend that involves a hex map.

There is an amazing guide here I couldn’t possibly top. I’m going to cover a few items that were absent I needed.  I used an axial coordinate system.  I haven’t seen a better method.

This post will cover:

Instantiating hex pieces, calculating Unity world coordinates from array coords.

I stored my hexagons in a 2d array let’s say HexMap[,].  The picture to the left shows an example.  Please note on an axial system (aka slanted) the Z axis is slanted and the Y axis is vertical.  To find where to place hexagons at their correct ‘world coordinate:”

Create a variable that stores the hex models radius (it’s side length in Unity)
Next calculate the apothem which is :

 Mathf.Sqrt(Mathf.Pow(radius, 2) – Mathf.Pow((radius / 2), 2));

Once you have the apothem you can easily calculate the world coordinates for any Hex based on the following :

x world coordinate = (x Array Coordinate * (1.5 * radius))
z world coordinate = ((z Array Coordinate * (2 * apothem)) + (x Array Coordinate * apothem))

Trimming the edges to create a Hex shaped map

To accomplish this look the array (map)  needs to be an odd number of hexes and square, the example above is 5×5.  To locate of the unwanted Hexagons marked in yellow above, red to the right.

amountToTrim = xMax / 2;  (floor division)
mapSize = (xSize-1)*2

Every tile that meets the following conditions needs trimmed:

if (x+z < hexAmountToTrim || x+z > (mapSize  – hexAmountToTrim ) ) {}

Marking a Border

I marked the border for two reasons.  I felt it would look nicer to add a trim piece to the map and my path finding algorithm does not check if coordinates are valid.  To handle this I flag border pieces as invalid/non-traversable so if/when they are reached they are ignored.

When generating the map catch the pieces and flag as a border only  if they are not caught while trimming the edges above.  This will only catch a 1 hex deep border.  If you want more you’ll need to check for different conditions.

(x + z < hexAmountToTrim + 1 || (x + z > ((mapSize  – 1) * 2) – (hexAmountToTrim + 1)) || z == 0 || x == 0 || z == mapSize  – 1 || x == mapSize  – 1)

Finding a hexgons neighbor’s

The example code will find the coords within a perimeter of three around the hexagon at the coordinates of 27,24.

1 int perimeter = 3;
2 int startingX = 27;
3 int startingZ = 24;
 
4 int areaToCutAround = startingX+startingZ;
5 for (int x = startingX - perimeter; x <= startingX + perimeter; x++)
6 {
7      for (int z = startingZ + perimeter; z >= startingZ - perimeter; z--)
8      {
9           if ((x + z < areaToCutAround - perimeter) || (x + z > (areaToCutAround + perimeter)))
10           {
11               //area being trimmed
12           }
13           else { //mark this x,z its within the perimeter }
14      }
15 }