public string ThumbImage;


using UnityEngine;
using Volplane;

public class Demo : VolplaneBehaviour
    void OnConnect(VPlayer player)
        // New element properties
        ElementProperties ep = new ElementProperties();
        ep.ThumbImage = "a-thumb-image.png";

        // Apply element properties
        player.ChangeElementProperties("joystick", ep);

Sets the thumb image of a relative joystick. Specified image must exist in the img folder in the WebGL template: Assets/WebGLTemplates/Volplane/img/ (images and fonts in your controller).