Using Python in the Blender Game Engine - Part 7

Hey. So here's part 7 of using Python in the BGE. In this one, we've created an enemy!
So, I went ahead and made an enemy from the base 'template' of our character - our enemy's a bit fatter, and has fangs hanging from his mouth. We give the enemy an 'enemy' property that will tell us when our Player runs into an enemy, so that we can deal with that. We also added a property, bullet, to our Bullet, so that we can tell when a bullet collides with an enemy. Finally, we've added a bullet collision sensor to our Enemy object, and an Enemy collision sensor to our player.


Okay, so now that we've done the necessary Blender property changes, we change our source code to do some extra things. We've added a new Python source file - the Enemy.py file. Let's take a look at our new module.

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from bge import logic
from bge import events

import math       

def Enemy():

    cont = logic.getCurrentController()
    sce = logic.getCurrentScene()
    obj = cont.owner
   
    bulletcol = cont.sensors['BulletCol']
   
    def Init():
        if not 'init' in obj:
            obj['init'] = 1
            obj['hp'] = 3                    # Set your HP at the beginning
   
    def Update():
   
        if bulletcol.positive:
            obj['hp'] -= 1                    # Decrement your HP one
            bullet = bulletcol.hitObject    # Get the bullet you collided with
            bullet.endObject()                # And destroy it
       
        if obj['hp'] <= 0:                    # If you have 0 HP
            obj.endObject()                    # Then destroy yourself
           
    Init()
    Update()
    
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Okay, so we see our Enemy's source code here. There's actually not too much here - we initialize the enemy object's health variable, and in the Update function, check the status of the Bullet Collision sensor. If the sensor returns true, then we decrement the enemy's health variable. When the health variable is equal to (or less than) 0, then the Enemy's been killed.

Next, we'll take a look at just the changed portion of our Player code. This portion of our Player code tests for the Player to collide with the Enemy, and when he does, what should happen...

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enemycol = cont.sensors['EnemyCol']

if enemycol.positive:
            print ("You've died. Great.")
            logic.restartGame()

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That's... Pretty much it. If the player collides with the enemy, then we print a simple debug line saying that we've been killed and restart the game. Nooooo! Heheh - so that's it for now, though in the future we can easily expand it to, say, display a screen that says, "You've died. Press Enter to restart", or something more complex than that, obviously.

I noticed that the code restarts the entire game, which works alright, but in the future, it should be changed to restart just the current scene, or better yet, restart from a checkpoint.

Note that in this whole tutorial series, we've been executing logic every game frame. While this may be necessary for certain games, some elements don't need to execute every frame, like the bullet - a collision sensor for the enemy checking for the bullet would be fine. Of course, we'll need to execute the bullet's movement code every frame, but for an example, the idea is the same.

So, that's about it. Download the Part 7 source code here:

Mirror 1: MediaFire
Mirror 2: Box.net