Gnat class

gnat.dart

class Gnat extends SpriteComponent with Tapable {
  Sprite sprite;
  double xMax, yMax;
  double xSpeed, ySpeed;
  double spriteSize;
  final spriteSpeed = 18.0;
  final spriteMin = 30.0;
  final spriteMax = 60.0;
  bool wall = false;
  bool remove = false;
  Gnat(this.sprite) : super.fromSprite(16.0, 16.0, sprite);

  @override
  void resize(Size size) {
    Random random = Random();
    spriteSize = spriteMin + random.nextDouble() * (spriteMax - spriteMin);
    width = spriteSize;
    height = spriteSize;

    xMax = size.width;
    x = random.nextDouble() * (xMax - width);
    xSpeed = 120.0 + random.nextDouble() * 120.0;
    if (random.nextBool()) xSpeed = -xSpeed;

    yMax = size.height;
    y = random.nextDouble() * (yMax - height);
    ySpeed = 60.0 + random.nextDouble() * 240.0;
    if (random.nextBool()) ySpeed = -ySpeed;
  }

  @override
  void update(double dt) {
    x += xSpeed * dt;
    if (((x >= xMax - width) && xSpeed > 0) || (x < 0.0)) {
      xSpeed = -xSpeed;
      wall = true;
    }
    y += ySpeed * dt;
    if (((y > yMax - height) && (ySpeed > 0)) || ((y < 35.0 && (ySpeed < 0)))) {
      ySpeed = -ySpeed;
      wall = true;
    }
    spriteSize += spriteSpeed * dt;
    if ((spriteSize > spriteMax) && wall) spriteSize = spriteMin;
    width = spriteSize;
    height = spriteSize;
    wall = false;

    renderFlipX = xSpeed > 0 ? false : true;
    angle = atan(ySpeed / xSpeed);
  }

  @override
  void onTapDown(TapDownDetails details) {
    MyGame.kills++;
    remove = true;
  }

  @override
  bool destroy() {
    return remove;
  }
}