Sensors

Sensors#

Actors have sensors that allow them to scan their environment — for example, to detect other actors at their position.

There are two ways to use sensors:

  1. You can actively detect other objects.

  2. You can register events that are triggered by sensor detection.

Actively Detecting Objects#

You can actively detect objects by using an actor’s sensors directly. Here’s an example of how it works:

import miniworlds 

world = miniworlds.World(200, 100)

r = miniworlds.Rectangle((10, 10), 50, 100)
c = miniworlds.Circle((200, 50), 20)

@c.register
def act(self):
    self.move_left()

@r.register
def act(self):
    actor = self.detect()  # Sensor detects objects at current position
    if actor:
        self.color = (255, 0, 0)  # Change color if an object is detected

world.run()

Output#

Explanation#

  • In the rectangle’s act() method, the sensor self.detect() checks if there’s another actor at the same position.

  • If another actor is detected, the rectangle changes color.

  • The variable actor contains the detected object, or None if nothing is found.

  • The line if actor is shorthand for if actor != None.

Registering Detection Events#

In the example above, actors actively checked for collisions. Alternatively, you can register a method that is automatically triggered when a sensor detects something:

from miniworlds import World, Rectangle, Circle

world = World(200, 100)

r = Rectangle((10, 10), 50, 100)
c = Circle((200, 50), 20)

@c.register
def act(self):
    self.move_left()

@r.register
def on_detecting(self, other):
    self.color = (255, 0, 0)  # Change color when another object is detected

world.run()

Explanation:#

  • The method on_detecting(self, other) is called automatically when an object is detected.

  • The other parameter refers to the detected object, allowing you to identify what was found.

Detecting Specific Objects#

Using sensors along with if-else statements, you can distinguish which object was detected:

import miniworlds 

world = miniworlds.World(200, 100)

r = miniworlds.Rectangle((10, 10), 50, 100)

c1 = miniworlds.Circle((200, 50), 20)
c2 = miniworlds.Circle((120, 50), 20)

@c1.register
def act(self):
    self.move_left()

@c2.register
def act(self):
    self.move_left()

@r.register
def on_detecting(self, other):
    if other == c1:
        self.color = (255, 0, 0)  # Turn red when detecting c1
    elif other == c2:
        self.color = (0, 255, 0)  # Turn green when detecting c2

world.run()

Output#

Explanation#

In the on_detecting method, the actor checks whether it has detected c1 or c2 and changes color accordingly.

Note

Note: Global Variables — Normally, variables are only accessible within a method.
Accessing global variables (as in this example) is simple but can cause unwanted side effects.
You’ll learn how to avoid this in the classes_first tutorial.

Example: Prevent Actors from Passing Through Walls#

Sensors can also be used to prevent actors from walking through walls. Here’s an example:

import miniworlds 

world = miniworlds.TiledWorld()
world.columns = 8
world.rows = 2
world.speed = 30

player = miniworlds.Actor()
player.add_costume("images/player_1.png")

wall = miniworlds.Actor((4, 0))
wall.add_costume("images/wall.png")

@player.register
def act(self):
    if player.position != (0, 4):
        player.direction = "right"
        player.move()

@player.register
def on_detecting(self, other):
    if other == wall:
        self.move_back()  # Move back when wall is detected

world.run()

FAQ#

My collision detection doesn’t work — what can I do?

First, test whether your method is even being called. Add a print statement like this:

@player.register
def on_detecting(self, actor):
    print(actor)

If nothing prints, the sensor is not working as expected.

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