Bundled Enemies

JsBattle comes with a set of enemies that are bundled with game distribution. This chapter explains some of their implementation details.

Dummy

Strategy

It literally does nothing. No movement, no shooting. Dummy could be a pretty good target for the start when you are testing your own tank.

Source Code

importScripts('lib/tank.js');

tank.init(function(settings, info) {
  settings.SKIN = 'forest';
});

tank.loop(function(state, control) {

});

Crawler

Strategy

Moving through the battlefield searching for the enemy. It turns every time when hitting a wall and keep going. Crawler is not actively scanning for enemies however, when it spots a target in front of the radar, it will shoot.

Source Code

importScripts('lib/tank.js');

var turnDirection, turnTimer;

tank.init(function(settings, info) {
  settings.SKIN = 'forest';
  // the direction where tank will turning.
  // 1 is clockwise, -1 is counter clockwise
  turnDirection = Math.random() < 0.5 ? 1 : -1;
  turnTimer = Math.round(Math.randomRange(0, 30));
})

tank.loop(function(state, control) {

  // when hit an obstacle, start turning until
  // time of turnTimer doesn't run out
  if(state.collisions.wall || state.collisions.enemy || state.collisions.ally) {
    turnTimer = Math.round(Math.randomRange(20, 50));
  }
  if(turnTimer > 0) {
    turnTimer--;
    // when turnTimer is on, do not move forward because there is
    // probably an obstacle in front of you. Turn instead.
    control.THROTTLE = 0;
    control.TURN = turnDirection;
  } else {
    // keep going forward at full speed
    control.THROTTLE = 1;
    control.TURN = 0;
  }
  // Shoot whenever you see an enemy
  if(state.radar.enemy) {
    control.SHOOT = 0.5;
  }
});

Crazy

Strategy

Not much strategy here. Just keep turning and shooting in all directions. Maybe some bullets will hit a target :) Could be a good enemy when testing bullets dodging algorithms.

Source Code

importScripts('lib/tank.js');

tank.init(function(settings, info) {
  settings.SKIN = 'forest';
});

tank.loop(function(state, control) {
  // keep shooting
  control.GUN_TURN = 1;
  // keep turning the radar because it is fun :)
  // there is no reason to do that :)
  control.RADAR_TURN = -1;
  // keep shooting bullets. Make them small
  // but shoot them frequently
  control.SHOOT = 0.1;

});

Chicken

Strategy

Goes to one of corners of the battlefield and shoot bullets around.

Source Code

importScripts('lib/tank.js');

/* moves tank in defined direction
* @param targetAngle - direction of movement
* @param state - state object of the tank
* @param control - control object of the tank
* @param done - callback executed when tank is close to the wall and the movement is over
*/
function goToDirection(targetAngle, state, control, done) {
  var angleDelta = Math.deg.normalize(targetAngle - state.angle);
  control.TURN = angleDelta * 0.2;
  // use boost to hide in corner ASAP
  control.BOOST = 1;

  // if any enemy on the radar - shoot!
  if(state.radar.enemy) {
    control.SHOOT = 1;
  } else {
    control.SHOOT = 0;
  }

  if(Math.abs(angleDelta) < 5) {
    // do not move forward if a tank is on your way
    if(state.collisions.enemy || state.collisions.ally) {
      control.THROTTLE = 0;
    } else {
      control.THROTTLE = 1;
    }
    // finish movement when close to a wall
    if(state.radar.wallDistance && state.radar.wallDistance < 50) {
      control.THROTTLE = 0;
      control.TURN = 0;
      control.BOOST = 0;
      done();
    }
  }
}

// strategy of moving north/south
// used at the beginning to go close to a wall
function goVerticalStrategy(state, control) {
  goToDirection(verticalAngle, state, control, function() {
    // when done - go to a corner
    strategy = goHorizontalStrategy;
  });
  control.DEBUG.strategy = "goVerticalStrategy:" + verticalAngle;
}

// strategy of moving east/west
// used when you are close to the wall so you can find a corner
function goHorizontalStrategy(state, control) {
  goToDirection(horizontalAngle, state, control, function() {
    // when done - start shooting
    strategy = shootStrategy;
  });
  control.DEBUG.strategy = "goHorizontalStrategy:" + horizontalAngle;
}

// shoot wave of bullets
function shootStrategy(state, control) {
  // 20*Math.sin(timer*0.1) cause rotation +-20 degrees over the time
  var angleDelta = Math.deg.normalize(shootAngle + 20*Math.sin(timer*0.1) - state.angle);
  control.TURN = angleDelta * 0.2;
  control.SHOOT = 0.1;
  control.DEBUG.strategy = "shootStrategy:" + shootAngle;
}


// strategy function that is currently used
var strategy;

// random direction of the tank that results in vertical movement (north or south)
var verticalAngle;
// random direction of the tank that results in horizontal movement (east or west)
var horizontalAngle;
// best direction to shoot when the tank is hidden i battlefield's corner
var shootAngle;
// timer used to change shooting angle over the time
var timer = 0;

tank.init(function(settings, info) {
  settings.SKIN = 'forest';

  // randomize direction of tank movement
  verticalAngle = Math.random() < 0.5 ? -90 : +90;
  horizontalAngle = Math.random() < 0.5 ? 0 : -180;
  // find direction that is opposite to the corner where the tank is
  shootAngle = Math.deg.normalize(verticalAngle + horizontalAngle)/2;
  if(horizontalAngle == 0) {
    shootAngle += 180;
  }

  // start from moving north/south
  strategy = goVerticalStrategy;
});

tank.loop(function(state, control) {
  // execute current strategy
  strategy(state, control);
  timer++;
});

Dodge

Strategy

There are a few elements of the strategy:

Find an enemy and keep it on your radar
Have perpendicularly position and move sideways to avoid bullets
Keep shooting the target

This tank is not moving through the battle field to search for an enemy. The only reason to move is to dodge a bullet.

Source Code

importScripts('lib/tank.js');

// keep information about all bullets that was spot
var bulletMap;
// avoid bullets by movement in random direction.
// avoidDirection = 1: move forward
// avoidDirection = -1: move backward
var avoidDirection;

// initialize your tank
tank.init(function(settings, info) {
  settings.SKIN = 'forest';
  bulletMap = [];
  changeAvoidDirection();
});

// randomly change direction of movement
function changeAvoidDirection() {
  avoidDirection = Math.random() > 0.5 ? -1 : 1;
}

tank.loop(function(state, control) {
  var i, bullet, bodyAngleDelta;

  // Rotate radar around to find an enemy.
  // When enemy found, keep radar beam on him
  if(state.radar.enemy) {
    // calculate angle of the enemy relating to your tank
    // this is the angle that you should aim your radar and gun to
    var enemyAngle = Math.deg.atan2(
      state.radar.enemy.y - state.y,
      state.radar.enemy.x - state.x
    )
    // calculate the difference between current and desired angle
    // of the radar.
    var radarAngleDelta = Math.deg.normalize(enemyAngle - (state.radar.angle + state.angle));
    // Turn the radar. If the difference between current and desired
    // angle is getting smaller, speed of turning will get lower too.
    // When the difference will be zero, turning will stop.
    control.RADAR_TURN = radarAngleDelta * 0.2;

    // Turn body of the tank so it is perpendicular to the enemyAngle
    // it will be easier to dodge bullets by moving back and forth
    bodyAngleDelta = Math.deg.normalize(enemyAngle - 90 - state.angle);
    if(Math.abs(bodyAngleDelta) > 90) bodyAngleDelta += 180;
    control.TURN = bodyAngleDelta * 0.2;

    // aim your gun at the enemy
    var gunAngleDelta = Math.deg.normalize(enemyAngle - (state.gun.angle + state.angle));
    control.GUN_TURN = gunAngleDelta*0.2;

    // shoot if you have aimed at the enemy
    control.SHOOT = 0.1;

  } else {
    // keep searching for opponents
    control.TURN = 0;
    control.RADAR_TURN = 1;
    bodyAngleDelta = 180;
  }

  // find bullets using radar
  for(i in state.radar.bullets) {
    bullet = state.radar.bullets[i];
    bullet.age = 0;
    bulletMap[bullet.id] = bullet;

    // calculate velocity components and distance between bullet and the tank
    bullet.vx = bullet.speed * Math.cos(bullet.angle*(Math.PI/180));
    bullet.vy = bullet.speed * Math.sin(bullet.angle*(Math.PI/180));
    bullet.tankDistance = Math.distance(state.x, state.y, bullet.x, bullet.y);
  }

  var bulletCount = 0;
  // predict position of all bullets scanned so far
  for(i in bulletMap) {
    bullet = bulletMap[i];
    if(!bullet) continue;
    // skip bullets that was not updated for long time
    // if they were not spotted by radar recently, they
    // probably are too far or hit something
    if(bullet.age > 50) {
      bulletMap[i] = null;
      continue;
    }
    // track age of the bullet so they can be removed if out-dated
    bullet.age++;
    // predict position of the bullet basing on its velocity
    bullet.x += bullet.vx;
    bullet.y += bullet.vy;
    // calculate distance between bullet and the tank. It will be used to
    // find how fast the distance is changing
    var newDistance = Math.distance(state.x, state.y, bullet.x, bullet.y);
    bullet.approachingSpeed = bullet.tankDistance - newDistance;
    bullet.tankDistance = newDistance;

    // If distance between tank and the bullet is negative, it means that it
    // is moving away from the tank and can be ignored (if will not hit it)
    //
    // In addition, if the speed of approaching the tank is too low, it means
    // that the trajectory of the bullet is away of the tank and it will
    // not hit it. Such bullets can be ignored too. The threshold value set
    // experimentally to 3.85
    if(bullet.approachingSpeed < 3.85) {
      bulletMap[i] = null;
      continue;
    }
    // count how many bullets are really dangerous and will probably hit the tank
    bulletCount++;
  }

  // avoid bullets when any of them is aiming at you and
  // you are rotated in a way that you can dodge it
  if(bulletCount && Math.abs(bodyAngleDelta) < 45) {
    control.BOOST = 1;
    control.THROTTLE = avoidDirection;
  } else {
    control.BOOST = 0;
    control.THROTTLE = 0;
    // change direction of bullets dodging
    changeAvoidDirection();
  }
});

Sniper

Strategy

Find a target by scanning surroundings and keep shooting it. Sniper never moves

Source Code

importScripts('lib/tank.js');

var power;

tank.init(function(settings, info) {
  settings.SKIN = 'forest';
  power = Math.random()*0.9 + 0.1;
})

tank.loop(function(state, control) {

  if(!state.radar.enemy) {
    control.RADAR_TURN = 1;
  } else {
    // find target angle to aim the enemy
    var targetAngle = Math.deg.atan2(
      state.radar.enemy.y - state.y,
      state.radar.enemy.x - state.x
    );

    var radarAngleDelta = Math.deg.normalize(targetAngle - (state.radar.angle + state.angle));

    // adjust radar direction to follow the target
    control.RADAR_TURN = radarAngleDelta*0.2;

    var gunAngleDelta = Math.deg.normalize(targetAngle - (state.gun.angle + state.angle));

    // adjust radar direction to follow the target
    control.GUN_TURN = gunAngleDelta * 0.2;

    if(Math.abs(gunAngleDelta) < 3) { // gun aimed at the target
      control.SHOOT = power;
    }
    control.DEBUG = "power=" + power.toFixed(2);
  }
});

Kamikaze

Strategy

Crush the enemy by diving into it. Kamikaze uses the boost to increase collision force.

Source Code

importScripts('lib/tank.js');

var turnDirection, turnTimer, direction, backTimer, boostTimer;

tank.init(function(settings, info) {
  settings.SKIN = 'forest';
  // the direction where tank will turning.
  // 1 is clockwise, -1 is couter clockwise
  turnDirection = Math.random() < 0.5 ? 1 : -1;
  turnTimer = Math.round(Math.randomRange(0, 30));
  direction = 1;
  backTimer = 0;
})

tank.loop(function(state, control) {

  if(state.collisions.enemy || state.collisions.ally) {
    backTimer = 12;
    boostTimer = 40;
  }
  if(backTimer > 0) {
    backTimer--;
    direction = -1;
  } else {
    direction = 1;
  }

  if(boostTimer > 0) {
    boostTimer--;
    control.BOOST = 1;
  } else {
    control.BOOST = 0;
  }
  control.THROTTLE = direction;

  if(!state.radar.enemy) {
    control.RADAR_TURN = 1;
    if(state.collisions.wall) {
      turnTimer = Math.round(Math.randomRange(20, 50));
    }
    if(turnTimer > 0) {
      turnTimer--;
      control.THROTTLE = 0;
      control.TURN = turnDirection;
    } else {
      control.THROTTLE = direction;
      control.TURN = 0;
    }

  } else {
    // find target angle to aim the enemy
    var targetAngle = Math.deg.atan2(
      state.radar.enemy.y - state.y,
      state.radar.enemy.x - state.x
    );

    // make sure that the angle is between (-180 and 180)
    var radarAngleDelta = Math.deg.normalize(targetAngle - (state.radar.angle + state.angle));

    // adjust radar direction to follow the target
    control.RADAR_TURN = radarAngleDelta*0.2;

    // make sure that the angle is between (-180 and 180)
    var tankAngleDelta = Math.deg.normalize(targetAngle - state.angle);


    // adjust radar direction to follow the target
    control.TURN = tankAngleDelta * 0.2;
  }

  control.DEBUG = {
    boost: state.boost
  };
  control.SHOOT = state.radar.enemy ? 0.3 : 0;
});

JsBattle Docs

Bundled Enemies

Dummy

Strategy

Source Code

Crawler

Strategy

Source Code

Crazy

Strategy

Source Code

Chicken

Strategy

Source Code

Dodge

Strategy

Source Code

Sniper

Strategy

Source Code

Kamikaze

Strategy

Source Code