I was doing some work on a Mystery Dungeon-like game, with procedurally generated meshes and a grid-based movement system.

I needed to check whether my controller was using the correct cell and whether my character mesh was positioned appropriately so I tried to check using a play-mode grid.

Grid in play mode using Gizmos
Current active cell is detected and displayed

Unity doesn’t offer a grid visualizer for play mode in Editor so you have to use your own system. There are 3 main possibilities:

  • Replace your ground material with a debug grid-material
  • Write a shader
  • Use Gizmos

In my case I decided to go with Gizmos since I was only interested with editor play-mode.
The logic is simple: create a monobehaviour and add a OnDrawGizmos function. You can also add this function to any other monobehaviour in your scene if you want to. Then, we’ll just iterate and draw lines in a grid format.

public class GridDraw: Monobehaviour {
  public int minX;
  public int maxX;
  public int minY;
  public int maxY;


  void OnDrawGizmos() {
    Gizmos.color = Color.white;
    
    Vector3 pos0 = new Vector3();
    Vector3 pos1 = new Vector3();
    for (int i = -minX; i < maxX; i++)
    {
        pos0.x = i;
        pos0.z = -minY;
        pos1.x = i;
        pos1.z = maxY;
        Gizmos.DrawLine(
            pos0,
            pos1
        );
        /*for (int j = 0; j < 100; j++) {

        }*/
    }

    for (int i = -minY; i < maxY; i++)
    {
        pos0.x = -minX;
        pos0.z = i;
        pos1.x = maxX;
        pos1.z = i;
        Gizmos.DrawLine(
            pos0,
            pos1
        );
}  

And that’s it for our grid! I’ll also draw a square over the current square in which my character is located. Add this code to your controller.

void OnDrawGizmos() {
  Gizmos.color = Color.cyan;
  Vector3 pos = new Vector3(Mathf.RoundToInt(transform.position.x), 0f, Mathf.RoundToInt(transform.position.z));
  Gizmos.DrawCube(pos + new Vector3(-0.5f, 0.5f, -0.5f), new Vector3(1f, 1f, 1f));

}   

The added Vector3 offsets the position to put it in the center of the cell so the square is drawn appropriately.