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Timers and countdowns: make things happen on time

A power-up that lasts ten seconds. A snake that steps eight times a second. A banner that fades after a moment. Games are full of things that happen on time.

The big idea

A game counts time in frames. every(n) is True once every n frames, and a countdown is a number that loses 1 each frame until it hits 0.

See it in code

1Start simple

every(8) is True on frame 0, frame 8, frame 16, and so on. Put a move inside it and the piece steps on a beat, not on every frame:

python
cell = 20
step_time = 8
head = Thing(x=110, y=250, size=18, color="lime green")
game.steps = 0

def play():
    if every(step_time):
        head.x = head.x + cell
        game.steps = game.steps + 1

def draw():
    paper("dark olive green")
    for col in range(32):
        line(x1=col * cell, y1=0, x2=col * cell, y2=HEIGHT, color="dark green", width=1)
    for row in range(24):
        line(x1=0, y1=row * cell, x2=WIDTH, y2=row * cell, color="dark green", width=1)
    head.draw()
    write(f"Steps: {game.steps}", x=320, y=30, color="white")
After two seconds, the snake's head has taken 15 steps:
A dark green lawn with faint grid lines and a bright green square that has stepped across to the right, with "Steps: 15" written at the top.

The game runs 60 frames a second. One step every 8 frames is about 7 or 8 steps a second. A smaller step_time makes a faster snake.

2A step further

A countdown makes something last a while. Set a number when the power starts, take 1 away on every frame, and act when it reaches 0:

python
paddle = Thing(x=320, y=430, width=90, height=18, color="white")
normal_width = 90
wide_width = 180
power_frames = 120
bar_scale = 3
game.power_timer = 0

def play():
    if key_pressed("space"):
        game.power_timer = power_frames
        paddle.width = wide_width
    if game.power_timer > 0:
        game.power_timer = game.power_timer - 1
        if game.power_timer == 0:
            paddle.width = normal_width

def draw():
    paper("black")
    paddle.draw()
    if game.power_timer > 0:
        box(x=320, y=60, width=game.power_timer * bar_scale, height=12, color="gold", corner=6)
    write(f"Power: {game.power_timer}", x=320, y=30, color="white")
A second after the power-up, half the time is left:
A black game window with a wide white paddle at the bottom, a gold power bar at the top about half its full length, and the words "Power: 60".

The paddle stays wide until the countdown ends, then one line shrinks it back. The gold bar reads the same number, so it shrinks as time runs out.

3In the arcade

Timers combine. This ship starts with a shield that lasts 180 frames. While it lasts, every() makes a ring blink around the ship, and a banner shows for the first 120:

python
ship = Thing(x=320, y=400, width=44, height=24, color="light sky blue")
shield_frames = 180
banner_frames = 120
blink_time = 6
game.shield = shield_frames
game.banner = banner_frames

def play():
    if game.shield > 0:
        game.shield = game.shield - 1
    if game.banner > 0:
        game.banner = game.banner - 1

def draw():
    paper("black")
    ship.draw()
    if game.shield > 0 and not every(blink_time):
        ring(x=ship.x, y=ship.y, size=70, color="deep sky blue", width=3)
    if game.banner > 0:
        write("Shield on!", x=320, y=220, size=56, color="gold")
    write(f"Shield: {game.shield}", x=320, y=30, color="white")
Partway through the shield, with the banner still showing:
A black space scene with a pale blue ship near the bottom ringed by a blue shield, a "Shield on!" banner in the middle, and a shield countdown at the top.

Two countdowns run side by side, and each one ends by itself. not every(blink_time) hides the ring for one frame in six, which is what makes it flicker.

The same idea, everywhere

Counting frames gives a game its sense of time. A serve after a pause. A wave banner. A sparkle that fades. A speed that goes up every thirty seconds.

Try it yourself

Change step_time = 8 to 4 in the snake game and watch the head race. Then set power_frames to 40 and see how short a power-up can feel.

The common mistake

Forgetting to stop at zero. Without the check if game.power_timer > 0, the number keeps falling: -1, -2, -3. Then == 0 never comes true again. Count down only while there's time left.

What it unlocks

Timers tick inside the game loop, once per frame. A countdown is a running total that goes down, and it often switches a game state when it ends.

Related concepts