Workshop › Pool › Step 28 of 33

Smaller steps

What we are doing

Hit a ball hard and at an angle, and it can go off in the wrong direction: at power 16 a ball moves 16 pixels a frame, so by the time we notice two balls touch they may overlap a lot, and the line between their centres is no longer the one at first contact. The fix: split each frame into SUB smaller steps.

```js
const SUB = 8 // physics steps per frame, so fast balls cannot jump through each other

    b.x += b.vx / SUB
    b.y += b.vy / SUB

  for (let i = 0; i < SUB; i++) step()
```

What it means

• Each step moves a ball by an eighth of its velocity; update runs eight steps per frame, so a frame still moves the full velocity.
• Collisions and pockets are checked in every small step.

Your turn

1. Under MAX_POWER write SUB.
2. In step, divide the velocities by SUB.
3. In update, replace step() with the for line.

Skills: Velocity and gravity, Collision detection

← Pull back and let go Predict the hit →

All steps

1. The room
2. The table
3. The cue ball
4. Draw the balls
5. The rack
6. Numbers on the balls
7. An aim line
8. Turn the aim
9. A shot is a velocity
10. Roll
11. Friction
12. Cushions
13. Aiming and rolling
14. Hide the aim while rolling
15. Count the shots
16. Balls that touch
17. Swap the push
18. Six pockets
19. In the pocket
20. Scratch
21. Balls left
22. Clear the table
23. Choose the power
24. A power bar
25. A slingshot
26. Press to aim
27. Pull back and let go
28. Smaller steps
29. Predict the hit
30. Draw the ghost ball
31. Where the hit ball goes
32. Your best
33. Build it yourself: two players