Mini-Game — Endless Runner — Part 1 (Movement)

By the end of this lesson you can:

• Scroll a ground strip left by decreasing its x offset each frame, and wrap it seamlessly.
• Apply gravity and an upward velocity so the player jumps on SPACE.
• Run the complete Part 1 game and see the player bounce on a scrolling ground.

In PZ-35 you applied gravity with vy += GRAVITY each frame. What does this print after 3 frames if GRAVITY = 0.5 and vy starts at 0?

vy = 0
GRAVITY = 0.5
for frame in range(3):
    vy += GRAVITY
    print(vy)

0.5
1.0
1.5

Think of a treadmill. The runner stays in the same spot while the belt moves under their feet. Our game works the same way: the player's x position never changes, but every frame we subtract a few pixels from the ground's x offset.

Ground scrolling

We keep one variable, ground_x, that starts at 0. Each frame we subtract SPEED. We draw the ground rectangle twice — once at ground_x and once at ground_x + WIDTH — so there is always something on screen. When ground_x falls below -WIDTH we reset it to 0 and the loop is invisible.

# update() — ground scroll
ground_x -= SPEED
if ground_x <= -WIDTH:
    ground_x = 0

Jump with gravity

The player has a vertical velocity vy. Pressing SPACE sets it to a negative number (upward in Pygame Zero's coordinate system — remember, y=0 is the top). Each frame gravity adds to it; when the player reaches the ground, we stop the fall.

# on_key_down — jump
def on_key_down(key):
    if key == keys.SPACE and player_y >= GROUND_Y:
        globals()["vy"] = -JUMP_SPEED

Faiz wants to build a side-scrolling runner. Save this as runner.py. We will extend it in PZ-39 to add obstacles and scoring.

Part A — constants and state

# runner.py — Endless Runner Part 1
import pgzrun

WIDTH = 600
HEIGHT = 300
TITLE = "Endless Runner"

GROUND_Y = 240          # y where the player stands
GRAVITY = 0.6
JUMP_SPEED = 12
SPEED = 4               # pixels the ground moves left per frame
GROUND_H = 60           # height of the ground strip

player_x = 80
player_y = GROUND_Y
vy = 0.0                # vertical velocity
ground_x = 0            # scroll offset

Part B — draw

def draw():
    screen.fill("lightyellow")
    # draw player as a coloured rectangle
    screen.draw.filled_rect(
        Rect((player_x - 15, player_y - 30), (30, 30)),
        "royalblue",
    )
    # draw scrolling ground (two copies side by side)
    screen.draw.filled_rect(
        Rect((ground_x, GROUND_Y), (WIDTH, GROUND_H)),
        "saddlebrown",
    )
    screen.draw.filled_rect(
        Rect((ground_x + WIDTH, GROUND_Y), (WIDTH, GROUND_H)),
        "saddlebrown",
    )

Part C — update and jump

def update():
    global player_y, vy, ground_x
    # gravity
    vy += GRAVITY
    player_y += vy
    # land on the ground
    if player_y >= GROUND_Y:
        player_y = GROUND_Y
        vy = 0.0
    # scroll ground
    ground_x -= SPEED
    if ground_x <= -WIDTH:
        ground_x = 0

def on_key_down(key):
    global vy
    if key == keys.SPACE and player_y >= GROUND_Y:
        vy = -JUMP_SPEED

pgzrun.go()

What you will see

An endless runner keeps the player at a fixed x position and scrolls the world leftward. Drawing the ground strip twice — at ground_x and ground_x + WIDTH — gives a seamless loop. Gravity plus an upward velocity on SPACE delivers a smooth jump. In Part 2 we add obstacles and a score.