Creating A Game With PHP Part 4: Side Scrolling Shooter (see https://www.hashbangcode.com/article/creating-game-php-part-4-side-scrolling-shooter)

shoot.php

<?php

class Entity {
  public $positionX = 0;
  public $positionY = 0;

  public function __construct($x, $y) {
    $this->positionX = $x;
    $this->positionY = $y;
  }
}

class Spaceship extends Entity {
  public $movementX = 0;
  public $movementY = 0;

  public $fire = FALSE;
}

class Enemy extends Entity {}

class Bullet extends entity {}


class Scene {
  public $height;
  public $width;

  public $ship;
  public $enemies = [];
  public $bullets = [];
  public $score = 0;

  public function __construct($width, $height) {
    $this->width = $width;
    $this->height = $height;
    $this->ship = new Spaceship(2, round($this->height / 2));
  }

  public function renderGame() {
    $output = '';

    for ($i = 0; $i < $this->height; $i++) {
      for ($j = 0; $j < $this->width; $j++) {
        if ($this->ship->positionX == $i && $this->ship->positionY == $j) {
          $cell = '>';
        }
        else {
          $cell = ' ';
        }
        foreach ($this->enemies as $enemy) {
          if ($enemy->positionX == $i && $enemy->positionY == $j) {
            $cell = 'X';
          }
        }
        foreach ($this->bullets as $bullet) {
          if ($bullet->positionX == $i && $bullet->positionY == $j) {
            $cell = '-';
          }
        }
        $output .= $cell;
      }
      $output .= PHP_EOL;
    }

    $output .= PHP_EOL;

    $output .= 'Score:' . $this->score . PHP_EOL;

    return $output;
  }

  public function moveEnemies() {
    foreach ($this->enemies as $enemyId => $enemy) {
      $enemy->positionY--;
      if ($enemy->positionY == 0) {
        // Remove the enemy if it goes beyond the left hand side of the scene.
        unset($this->enemies[$enemyId]);
        continue;
      }
      foreach ($this->bullets as $bulletId => $bullet) {
        if ($bullet->positionX == $enemy->positionX && ($bullet->positionY == $enemy->positionY || $bullet->positionY == $enemy->positionY - 1)) {
          unset($this->enemies[$enemyId]);
          unset($this->bullets[$bulletId]);
          $this->score++;
        }
      }
    }
  }

  public function moveBullets() {
    foreach ($this->bullets as $bullet) {
      $bullet->positionY++;
    }
  }

  public function shoot() {
    if ($this->ship->fire == TRUE) {
      $this->bullets[] = new Bullet($this->ship->positionX, $this->ship->positionY + 1);
      $this->ship->fire = FALSE;
    }
  }

  public function spawnEnemies() {
    if (count($this->enemies) < 15) {
      $y = rand($this->width, $this->width * 2);
      $x = rand(0, $this->height - 1);
      $this->enemies[] = new Enemy($x, $y);
    }
  }

  public function gameOver() {
    foreach ($this->enemies as $enemy) {
      if ($this->ship->positionX == $enemy->positionX && $this->ship->positionY == $enemy->positionY) {
        die('dead :(');
      }
    }
  }

  public function moveShip() {
    $this->ship->positionX += $this->ship->movementX;
    $this->ship->positionY += $this->ship->movementY;

    $this->ship->movementX = 0;
    $this->ship->movementY = 0;

    if ($this->ship->positionX < 0) {
      $this->ship->positionX = 0;
    }
    if ($this->ship->positionX >= $this->height) {
      $this->ship->positionX = $this->height - 1;
    }
    if ($this->ship->positionY < 0) {
      $this->ship->positionY = 0;
    }
    if ($this->ship->positionY > $this->width / 4) {
      $this->ship->positionY = $this->width / 4;
    }
  }

  public function action($stdin) {
    // Listen to the button being pressed.
    $key = fgets($stdin);
    if ($key) {
      $key = $this->translateKeypress($key);
      switch ($key) {
        case "UP":
          $this->ship->movementX = -1;
          $this->ship->movementY = 0;
          break;
        case "DOWN":
          $this->ship->movementX = 1;
          $this->ship->movementY = 0;
          break;
        case "RIGHT":
          $this->ship->movementX = 0;
          $this->ship->movementY = 1;
          break;
        case "LEFT":
          $this->ship->movementX = 0;
          $this->ship->movementY = -1;
          break;
        case "ENTER":
        case "SPACE":
          $this->ship->fire = TRUE;
          break;
        case "ESC":
          die();
      }
    }
  }

  private function translateKeypress($string) {
    switch ($string) {
      case "\033[A":
        return "UP";
      case "\033[B":
        return "DOWN";
      case "\033[C":
        return "RIGHT";
      case "\033[D":
        return "LEFT";
      case "\n":
        return "ENTER";
      case " ":
        return "SPACE";
      case "\e":
        return "ESC";
    }
    return $string;
  }
}

$seed = 1;
srand($seed);

$scene = new Scene(50, 10);

system('stty cbreak -echo');
$stdin = fopen('php://stdin', 'r');
stream_set_blocking($stdin, 0);

while (1) {
  system('clear');
  $scene->action($stdin);
  $scene->moveShip();
  $scene->shoot();
  $scene->moveBullets();
  $scene->moveEnemies();
  echo $scene->renderGame();
  $scene->gameOver();
  $scene->spawnEnemies();
  usleep(100000);
}