node-haxball/examples/plugins/modifyBallSize.js

The most powerful and lightweight API that allows you to develop your original Haxball(www.haxball.com) host, client, and standalone applications both on node.js and browser environments and also includes every possible hack and functionality that you can

module.exports = function(API){
  const { OperationType, VariableType, ConnectionState, AllowFlags, Direction, CollisionFlags, CameraFollow, BackgroundType, GamePlayState, BanEntryType, Callback, Utils, Room, Replay, Query, Library, RoomConfig, Plugin, Renderer, Errors, Language, EventFactory, Impl } = API;

  Object.setPrototypeOf(this, Plugin.prototype);
  Plugin.call(this, "modifyBallSize", true, {
    version: "0.1",
    author: "abc",
    description: `This plugin can modify ball size on demand.`,
    allowFlags: AllowFlags.CreateRoom | AllowFlags.JoinRoom // We allow this plugin to be activated on both CreateRoom and JoinRoom.
  });

  this.defineVariable({
    name: "coefficient",
    description: "This number is multiplied with the original ball radius", 
    type: VariableType.Number,
    value: 1,
    range: {
      min: 0,
      max: 1000,
      step: 0.1
    }
  });
  
  var that = this, originalExtrapolate = null;
  
  this.initialize = function(){
    originalExtrapolate = that.room.extrapolate;
    that.room.extrapolate = function(...params){
      var state = originalExtrapolate.call(that.room, ...params);
      var ball = state.gameState?.physicsState.discs[0];
      if (ball)
        ball.radius *= that.coefficient;
      return state;
    };
  };
  
  this.finalize = function(){
    that.room && (that.room.extrapolate = originalExtrapolate);
  };
}