Get a random Y position for a new enemy being spawned, which is NOT "crowded" (no other active enemy must have the same rough Y position).

gistfile1.js

function getYPositionNotCrowded() {
  var radius   = 8
  var y        = 0
  var blocking = false

  do {
    y = randIntRange(height, canvas.height - height)
    for (var i = 0; i < enemies.length; ++i)
      if (enemies[i].isActive)
        blocking = y > enemies[i].y && y < (enemies[i].y + height)
  } while (blocking)

  return y
}


/*

  // Get a random Y position for a new enemy being spawned, which is NOT "crowded" (no other active enemy must have the same rough Y position).
  function getYPositionNotCrowded()
  {
    var theHeight = 8;
    var theY = 0;
    var numberOfEnemiesWhoAreNotBlocking = 0;
    var numberOfActiveEnemies = 0;

    while (1)
    {
      theY = randIntRange(theHeight, canvas.height - theHeight);
      numberOfEnemiesWhoAreNotBlocking = 0;
      numberOfActiveEnemies = 0;

      for (var i = 0; i < enemies.length; i++)
      {
        if (enemies[i].isActive)
        {
          numberOfActiveEnemies++;

          if (!(theY > enemies[i].y && theY < (enemies[i].y + theHeight)))
            numberOfEnemiesWhoAreNotBlocking++;
        }
      }

      if (numberOfEnemiesWhoAreNotBlocking == numberOfActiveEnemies)
        break;
    }

    return theY;
  }

*/