How to Prevent Ball from Crossing Boundaries in PyGame?

How to Make a Ball Bounce Off Walls with PyGame

Problem

In PyGame, how do you prevent a ball from going inside a wall when it hits one?

Solution

Nested Loops:

The issue arises from using multiple nested loops. It's more efficient to handle movement within the application loop.

<code class="python">while run:                     
    # Handle movement continuously
    box.y -= box.vel_y        
    box.x += box.vel_x</code>

Boundary Definition:

Define a rectangular region for ball movement using a pygame.Rect object:

<code class="python">bounds = window.get_rect() # full screen
bounds = pygame.Rect(450, 200, 300, 200)  # rectangular region</code>

Boundary Collision Handling:

Update ball direction when it intersects with the boundaries:

<code class="python">if box.x - box.radius < bounds.left or box.x + box.radius > bounds.right:
    box.vel_x *= -1 
if box.y - box.radius < bounds.top or box.y + box.radius > bounds.bottom:
    box.vel_y *= -1</code>

Example

<code class="python">box = Circle(600,300,10)

run = True
start = False
clock = pygame.time.Clock()

while run:                     
    clock.tick(120)  

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            run = False

    keys = pygame.key.get_pressed()
    if keys[pygame.K_SPACE]:
        start = True

    bounds = pygame.Rect(450, 200, 300, 200)
    if start:
        box.y -= box.vel_y        
        box.x += box.vel_x

        if box.x - box.radius < bounds.left or box.x + box.radius > bounds.right:
            box.vel_x *= -1 
        if box.y - box.radius < bounds.top or box.y + box.radius > bounds.bottom:
            box.vel_y *= -1 

    window.fill((0,0,0))
    pygame.draw.rect(window, (255, 0, 0), bounds, 1)
    pygame.draw.circle(window, (44,176,55), (box.x, box.y), box.radius)
    pygame.display.update()</code>

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