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10. PIXEL COLLISIONS

 

 

YOU LEARN HERE...

 

precise collision detection using so-called pixel collisions. Unlike grid collisions, where two actors are located in the same cell, here two actors collide when at least two pixels of their figures overlap. The GameGrid module provides the necessary functions to detect such collisions.

 

 

EXAMPLES

 

 

 Example 1: Two rectangular figures move freely in the game window and reflect off the window edge. When they collide, a sound is emitted and the two sticks change their direction of movement by 180°.
 

The collisions are recorded as events. The collide() method is called..

Mit stick1.addCollisionActor(stick2)tells Stick1 to react to collisions with stick2. Even if the two figures touch at their corners, a collision event is triggered.

With return 10, you specify the number of simulation cycles until the collision event is reactivated. Here you have to wait a little until the sticks are no longer touching.

  

Program: 

from gamegrid import *
from soundsystem import *

# --------------------- class Stick ----------------------------------
class Stick(Actor):
    def __init__(self):
        Actor.__init__(self, True, "sprites/stick.gif", 2)  
   
    def act(self):
        step = 1
        loc = self.getLocation()
        dir = (self.getDirection() + step) % 360;
        if loc.x < 50:
            dir = 180 - dir
            self.setLocation(Location(55, loc.y))
        if loc.x > 450:
            dir = 180 - dir
            self.setLocation(Location(445, loc.y))
        if loc.y < 50:
            dir = 360 - dir
            self.setLocation(Location(loc.x, 55))
        if loc.y > 450:
            dir = 360 - dir
            self.setLocation(Location(loc.x, 445))
        self.setDirection(dir)
        self.move()

    def collide(self, actor1, actor2):
        actor1.setDirection(actor1.getDirection() + 180)
        actor2.setDirection(actor2.getDirection() + 180)
        play()
        return 10

# --------------------- main -----------------------------------------
makeGameGrid(500, 500, 1, False)
setSimulationPeriod(10)
stick1 = Stick()
addActor(stick1, Location(200, 200), 30)
stick2 = Stick()
addActor(stick2, Location(400, 400), 30)
stick2.show(1)
stick1.addCollisionActor(stick2)
show()
doRun()
openSoundPlayer("wav/ping.wav")
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Example 2: Five coloured balls move freely around the playing field and bounce off the edges. As soon as one ball touches another, a collision is triggered. Each ball bounces back at the same angle at which it rolled in, and a sound is played.

The collide() method defines the behaviour of the two colliding balls. With balls[i].addCollisionActor(balls[k]), collision with all other balls is activated for each ball.

  

Program: 

from gamegrid import *
from soundsystem import *
from random import randint

# --------------------- class Ball ----------------------------------
class Ball(Actor):

   def __init__(self):
      Actor.__init__(self, True, "sprites/peg.png", 5)  
      
   def act(self):
      step = 1
      loc = self.getLocation()
      dir = (self.getDirection() + step) % 360;

      if loc.x < 20:
         dir = 180 - dir
         self.setLocation(Location(20, loc.y))
      if loc.x > 480:
         dir = 180 - dir
         self.setLocation(Location(478, loc.y))
      if loc.y < 20:
         dir = 360 - dir
         self.setLocation(Location(loc.x, 22))
      if loc.y > 480:
         dir = 360 - dir
         self.setLocation(Location(loc.x, 478))
      self.setDirection(dir)
      self.move()

   def collide(self, actor1, actor2):
      actor1.setDirection(actor1.getDirection() + 180)
      actor2.setDirection(actor2.getDirection() + 180)
      play()
      return 10

# --------------------- main -----------------------------------------
makeGameGrid(500, 500, 1, False)
setSimulationPeriod(10)
balls = []
for i in range(5):
   ball = Ball()
   ball.show(i)
   addActor(ball, Location(randint(30, 470), randint(30, 470)))
   balls.append(ball)

for i in range(5):
   for k in range(i + 1, 5):
      balls[i].addCollisionActor(balls[k])

openSoundPlayer("wav/ping.wav")  
show()
doRun()
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Example 3: A mouse-controlled arrow can pop balloons.
20 balloons are generated at randomly selected positions. You can move the arrow by holding down the mouse button. When the arrow tip touches a balloon, it pops and a sound is played.

With dart.addCollisionActor(ballon) , each balloon becomes a collision partner for the arrow.
actor2.removeSelf() makes the hit balloon disappear.

  

Program: 

from gamegrid import *
from soundsystem import *
from random import randint

# --------------------- class Dart --------------------------
class Dart(Actor, GGMouseListener):
    def __init__(self):
        Actor.__init__(self, True, "sprites/dart.gif") 
        self.oldLocation = Location()
    
    def mouseEvent(self, e):
        location = toLocationInGrid(e.getX(),e.getY())
        self.setLocation(location)
        self.oldLocation.x = location.x
        self.oldLocation.y = location.y

    def collide(self, actor1, actor2):
        play()
        actor2.removeSelf()
        return 5

# --------------------- main -----------------------------------
makeGameGrid(600, 600, 1, None, "sprites/town.jpg", False)
setTitle("Move dart with mouse to pick the balloon")
setSimulationPeriod(50)
dart = Dart()
addActor(dart, Location(100, 300))
addMouseListener(dart, GGMouse.lDrag)
for i in range(20):
    balloon = Actor("sprites/balloon.gif")
    addActor(balloon, Location(randint(50,550),randint(50,550)))
    dart.addCollisionActor(balloon)
show()
openSoundPlayer("wav/explode.wav")
doRun()
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REMEMBER YOU...
 

Collisions are recorded as events. The method collide(self, actor1, actor2) is called, which defines what should happen when the two actors collide.
actor1.addCollisionActor(actor2) tells actor1 to react to collisions with actor2.

 

 

TO SOLVE BY YOURSELF
 

1.

Two aliens move freely in the game window and reflect off the window edge. When they collide, a sound is heard and the two aliens change their direction of movement by 180°.
For the aliens, use the sprites alien_0.gif and alien_1.gif, and for the background, use the image sprites/town.jpg from the GameGrid image library.		  
 

2.

60 aliens move freely around the playing field and bounce off the edges. As soon as one alien touches another, a collision is triggered. The first alien bounces back at the same angle at which it rolled in, and the second alien disappears from the game window. Let the programme run until only one alien remains.

Use the sprite alien.png for the aliens.

  
 

 
3.

Nemo eliminates jellyfish.
30 jellyfish are generated at randomly selected positions. When the mouse-controlled Nemo touches a jellyfish, it is destroyed.

For the jellyfish, use the image
jellyfisch.gif’ and for Nemo, use the image
nemo.gif.