node-haxball/examples/plugins/autoPlay_followBall.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, "autoPlay_followBall", true, { // "autoPlay_followBall" is plugin's name, "true" means "activated just after initialization". Every plugin should have a unique name.
    version: "0.4",
    author: "abc",
    description: `This is an auto-playing bot that always follows the ball blindly, and kicks it whenever it is nearby without any direction checking. This bot uses real events and controls real players.`,
    allowFlags: AllowFlags.CreateRoom | AllowFlags.JoinRoom // We allow this plugin to be activated on both CreateRoom and JoinRoom.
  });

  this.defineVariable({
    name: "minCoordAlignDelta",
    description: "Minimum delta value for coordinate alignment", 
    type: VariableType.Number,
    value: 0.5, 
    range: {
      min: 0,
      max: 10,
      step: 0.5
    }
  });

  this.defineVariable({
    name: "minKickDistance",
    description: "Minimum distance between ball and bot player for the bot player to start kicking the ball", 
    type: VariableType.Number,
    value: 8, 
    range: {
      min: 0,
      max: 15,
      step: 0.5
    }
  });

  var that = this;
  
  this.onGameTick = function(customData){

    // ensure extrapolation of the room state before calculating stuff.
    that.room.extrapolate();

    // get the extrapolated disc of the data object of the current player
    var cp = that.room.currentPlayer, playerDisc = cp?.disc?.ext;
    if (!playerDisc) // check or else error occurs after changing a player's team to spectators, if the player is not actually in the game, or the game is stopped.
      return;

    // get the extrapolated game state object
    var { state, gameState, gameStateExt } = that.room;
    gameState = gameStateExt || gameState;

    // get the original extrapolated data object of the ball
    var ball = gameState.physicsState.discs[0];

    // get the coordinates of the ball
    var {x, y} = ball?.pos || {};

    // if ball is not reachable, do nothing.
    if (x==null || isNaN(x) || !isFinite(x) || y==null || isNaN(y) || !isFinite(y)) // check 
      return;

    // speed: playerDisc.speed.x, playerDisc.speed.y
    // radius: playerDisc.radius

    // calculate delta difference for both x and y axis.
    var deltaX = x - playerDisc.pos.x, deltaY = y - playerDisc.pos.y, dirX, dirY, kick;

    // x direction:
    if (Math.abs(deltaX) < that.minCoordAlignDelta) // we can omit small delta.
      dirX = 0;
    else 
      dirX = Math.sign(deltaX); // direction is +1 or -1, depending on the delta difference

    // y direction
    if (Math.abs(deltaY) < that.minCoordAlignDelta) // we can omit small delta.
      dirY = 0;
    else
      dirY = Math.sign(deltaY); // direction is +1 or -1, depending on the delta difference

    // kick is true if the distance between ball and player is less than minKickDistance
    kick = (deltaX * deltaX + deltaY * deltaY < (playerDisc.radius + ball.radius + that.minKickDistance) * (playerDisc.radius + ball.radius + that.minKickDistance));

    // apply current keys
    that.room.setKeyState(Utils.keyState(dirX, dirY, kick));
  };
};