Why Does My Pong Ball Slide Along the Paddle Instead of Bouncing?

Ball Refuses to Bounce off Paddle in Pong Game

In certain instances, players may encounter an anomaly in their pong game: the ball inexplicably slides along the paddle instead of bouncing off it. This aberrant behavior stems from a subtle flaw in the collision detection mechanism.

Collision Detection Flaws

When the ball collides with the paddle rectangle, its direction is altered. However, sometimes the collision occurs not on the paddle's front but at its top or bottom. While the collision is detected and the ball's trajectory is reversed appropriately, the ball has already penetrated deeply into the paddle.

In the subsequent frame, the ball cannot exit the collision area. As a result, a second collision is detected, reversing the ball's direction once more. This pattern repeats until the ball eventually "falls" off the paddle's bottom edge.

Resolving the Issue

To rectify this problem, several solutions exist. One approach involves adjusting the ball's direction. Instead of simply reversing it, we can set the direction to the left (or right) upon a collision with the left (or right) paddle, respectively:

if ball.colliderect(paddleLeft):
    move_x = abs(move_x)
if ball.colliderect(paddleRight):
    move_x = -abs(move_x) 

Alternatively, we can adjust the ball's position precisely. Upon a collision with the left (or right) paddle, we ensure that the ball's left (or right) edge is situated to the right (or left) of the corresponding paddle boundary:

if ball.colliderect(paddleLeft):
    move_x *= -1
    ball.left = paddleLeft.right
if ball.colliderect(paddleRight):
    move_x *= -1
    ball.right = paddleRight.left

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