without arrays

spc_inv.pde

MySpaceship S1;
AllienSpaceship A1, A2, A3;

float x = 30;
int counter;

void setup() {
  size(400, 400);
  counter = 0;
  S1 = new MySpaceship();
  A1 = new AllienSpaceship();
  A2 = new AllienSpaceship();
  A3 = new AllienSpaceship();
}

void draw() {
  background(0);

  textSize(10);
  fill(#42FC1F);
  text(">>SCORE:" + counter, 10, 20);

  noStroke();
  fill(#42FC1F);
  rectMode(CORNER);
  rect(0, height - 2, width, 2);

  S1.display();
  S1.control();

  A1.display();
  A1.attack();
  
  A2.display();
  A2.attack();
  
  A3.display();
  A3.attack();

  if (mousePressed == true) {
    S1.laser();
    if (S1.hit(A1)) {
      counter += 1;
      A1 = new AllienSpaceship();
    }
    
    if (S1.hit(A2)) {
      counter += 1;
      A2 = new AllienSpaceship();
    }
    
    if (S1.hit(A3)) {
      counter += 1;
      A3 = new AllienSpaceship();
    }
  }

  if (A1.win(S1)) {
    background(0);
    textSize(10);
    fill(#42FC1F);
    text(">>SCORE:" + counter, width / 2, height / 2);
    noLoop();
  }
  
  if (A2.win(S1)) {
    background(0);
    textSize(10);
    fill(#42FC1F);
    text(">>SCORE:" + counter, width / 2, height / 2);
    noLoop();
  }
  
  if (A3.win(S1)) {
    background(0);
    textSize(10);
    fill(#42FC1F);
    text(">>SCORE:" + counter, width / 2, height / 2);
    noLoop();
  }  
}

class AllienSpaceship {
  float x, y, w, h, speedY;

  AllienSpaceship() {
    w = 30;
    h = w;
    x = random(50, width - 50);
    y = h;
    speedY = 1;
  }

  void display() {
    rectMode(CENTER);
    noStroke();
    fill(255);

    rect(x, y, w, 1.6 * h / 5);
    rect(x, y + h / 5, w / 1.6, h / 5);
    rect(x, y + 2 * h / 5, w / 1.3, h / 5);
    fill(#2C0E20);
    rect(x, y, w / 10, h / 4);
  }

  void attack() {
    x = x + random(- 5, 5);
    y = y + speedY;
  }

  boolean win(MySpaceship other) {
    if (y > height) return true;
    if (x + w/2 >= other.x - other.w/2 && x - w/2 <= other.x + other.w/2) {
      if (y + h/2 >= other.y - other.h/2) {
        return true;
      }
    }
    return false;
  }
}


class MySpaceship {
  float x, y, w, h, speed;

  // w = spaceShipWidth; h = spaceShipHeight;
  // spaceShip consist of 3 parts.

  MySpaceship() {
    speed = 5;
    w = 30;
    h = w;
    x = width / 2;
    y = height - h;
  }

  void display() {
    rectMode(CENTER);
    noStroke();
    fill(#42FC1F);

    rect(x, y, w, 1.6 * h / 5);
    rect(x, y - h / 5, w / 1.6, h / 5);
    rect(x, y - 2 * h / 5, w / 10, h / 5);
  }

  void control() {
    if (keyPressed) {
      if (key == 'd') {
        x = x + speed;
      } else if (key =='a') {
        x = x - speed;
      }
    }

    if (x + w / 2 > width) {
      x = - w / 2;
    } else if (x + w / 2 < 0) {
      x = width - w / 2;
    }
  }

  void laser() {
    fill(#FF21A7); 
    rectMode(CORNERS);
    rect(x, y - h / 1.6, x + w / 20, 0);
  }

  boolean hit(AllienSpaceship other) {
    if (x > other.x - other.w / 2 && x < other.x + other.w / 2) return true;
    return false;
  }
}