Lesson 3

Jupyter Notebooks

Run the jupyter notebook command to get started. See the tutorial for a list of shortcuts here.

The Update Design Pattern

Each sprite created has an update function called repeatedly from the time created until the time deleted or if the application is closed.

The Sprite Life-Cycle

sprite = window.create_sprite()
The window creates a new sprite object and calls the sprites on_create() method. Then it returns the .sprite object.
The on_update(self, dt) method is called repeatedly at about 60 frames per second. If you subclass the sprite, you can define a custom on_update(self, dt) method to add new behavior (e.g., movement, collision detection, image and color changed, etc.) to your sprite. The dt argument can tell us the precise time since the last on_update() was called.

Keyboard Interaction

The `KeyCode` class

Each key that can be pressed on a keyboard is defined by a constant value defined by the KeyCode class.

Checking For Key Events

In a sprite’s on_update method we can detect three possible types of key events. We use KeyCode constant values to check for specific keys.

window.is_key_down(KeyCode.A)
window.is_key_press(KeyCode.B)
window.is_key_up(KeyCode.C)

What is the difference? When would we want to use one vs. the other?

These three methods all return boolean values and are used together with an if statement to detect the correct key event. For example, the code below will continuously move a sprite to the left while a user holds down the A key.

def on_update(self, dt):
    if window.is_key_press(KeyCode.A):
        self.x -= 5