Workshop › Pinball › Step 12 of 42

Bounce off the wall

What we are doing

Pushing the ball out is not enough: its speed still points into the wall. We reflect the part of the velocity that goes into the wall, keeping half of it (bounce = 0.5).

```js
const vn = ball.vx * nx + ball.vy * ny
if (vn < 0) {
  ball.vx -= (1 + bounce) * vn * nx
  ball.vy -= (1 + bounce) * vn * ny
}
```

What it means

• vn is the dot product of the velocity and the normal: how fast the ball moves out of the wall. Negative means into it.
• Only then do we change the velocity: taking away vn along the normal would stop it; taking away (1 + bounce) × vn sends it back out at bounce times the speed.

Your turn

In hitSegment, write the five lines under ball.y = py + ny * R, above return true.

Skills: Velocity and gravity, Collision detection

← Push the ball out Small steps and a speed limit →

All steps

1. Paint the table
2. Draw one wall
3. A list of walls
4. The game loop
5. A ball in the lane
6. Draw the ball
7. Move by the velocity
8. Launch with Space
9. Gravity
10. Does the ball touch a wall?
11. Push the ball out
12. Bounce off the wall
13. Small steps and a speed limit
14. Ready or playing
15. The next ball
16. Three bumpers
17. The ball meets a bumper
18. A bumper kicks
19. A score and a fresh start
20. Points for every hit
21. Remember which bumper was hit
22. Light it up
23. Lit for a moment, points once
24. Two flippers
25. Where is the tip?
26. Flippers stop the ball
27. Which keys are held?
28. Which way to turn
29. Flip!
30. A moving wall
31. The flipper throws
32. Three balls
33. Balls left and game over
34. Play again
35. Remember the best score
36. Launch on letting go
37. Pull the spring
38. Show the spring
39. Two thumbs
40. Pull with a finger
41. Tap to play again
42. Build it yourself: slingshots