week13.py

# Week 13: Pygame Zero - Moving Dot (No images needed)
# Goal: Learn Pygame Zero basics - automatic game loop, update() and draw()
# Run with: pgzrun week13.py (or just F5 in Thonny if pgzero installed)

# === CONFIGURATION ===
# These MUST be at the top, outside functions
# Pygame Zero uses these to create the window
WIDTH = 600
HEIGHT = 400

# === GAME VARIABLES ===
# Position of the dot
x = WIDTH // 2   # Start at horizontal center (// = integer division)
y = HEIGHT // 2  # Start at vertical center

# Velocity (speed and direction)
vx = 3  # Positive = move right, negative = move left

# === UPDATE FUNCTION ===
# Called automatically 60 times per second!
# This is where game logic happens (movement, collisions, etc.)
def update():
    global x, vx  # Need 'global' to modify variables from outside function
    
    # Move the dot
    x += vx  # Same as: x = x + vx
    
    # Bounce off edges
    if x < 10 or x > WIDTH - 10:
        vx = -vx  # Reverse direction (flip the sign)

# === DRAW FUNCTION ===
# Called automatically after each update()
# This is where we display everything
def draw():
    screen.clear()  # IMPORTANT: Erase previous frame
    
    # Draw background text
    screen.draw.text("Moving Dot", (20, 20))
    
    # Draw the dot (filled circle)
    # Parameters: (x, y), radius, color
    screen.draw.filled_circle((x, y), 10, "white")

# === NO MAINLOOP NEEDED! ===
# Pygame Zero runs the game loop automatically
# It calls update() then draw(), 60 times per second
# This is MUCH simpler than turtle.ontimer()

# === KEY CONCEPTS ===
# 1. WIDTH/HEIGHT create window (must be CAPITALS)
# 2. update() = change game state
# 3. draw() = show game state
# 4. screen is automatic (no import needed!)
# 5. 60 FPS = 60 frames (updates) per second

# === TRY THIS ===
# 1. Change vx to 5 (faster)
# 2. Remove screen.clear() - see trails!
# 3. Add vy for vertical movement
# 4. Change color to "red" or "yellow"