Workshop › Pinball › Step 28 of 42

Which way to turn

What we are doing

Each frame a flipper picks a target (up if its key is held, rest otherwise) and a turning speed towards it: FLIP_SPEED a frame, or just the rest of the way when it is nearly there.

```js
const FLIP_SPEED = 0.25 // radians per frame

  for (const f of flippers) {
    // Up while the key is held, back down when it is let go, and stop at either end.
    const target = pressed[f.key] ? f.up : f.rest
    const dir = Math.sign(target - f.angle)
    f.speed = Math.abs(target - f.angle) < FLIP_SPEED ? (target - f.angle) : dir * FLIP_SPEED
  }
```

What it means

• pressed[f.key] reads the field named by f.key: pressed.left for the left flipper.
• Math.sign gives 1, -1 or 0: which way to turn. Math.abs drops the minus: how far there is to go.
• If the distance is less than one step, the speed is exactly the distance; otherwise a full step in direction dir.
• Using dir instead of assuming "up is smaller" makes the same code right for the right flipper, whose up angle is the bigger one.

Your turn

1. Under FLIPPER_LENGTH write FLIP_SPEED.
2. In update, under the flash = ... line, write the for loop.

Skills: Velocity and gravity, Game states

← Which keys are held? Flip! →

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