Workshop › Scorched Earth-style Artillery › Step 22 of 23

The atan2 trap

What we are doing

Point below your barrel and the barrel points into the ground: atan2 happily gives angles between 0 and π there (down is positive on a canvas). The barrel must stay in the upper half, so below it we aim flat to that side instead.

```js
// Below the barrel, atan2 gives an angle between 0 and π: aim flat to that side instead.
t.angle = angle > 0 ? (angle > Math.PI / 2 ? -Math.PI : 0) : angle
```

What it means

• A positive angle means "below": more than a quarter turn is the left side (flat left, −π), less is the right side (0).
• Negative angles are already up, so they are kept.

Your turn

Above the atan2 line, write the comment; replace t.angle = angle with the checked version.

Skills: Velocity and gravity

← Drag and let go Build it yourself: a trail →

All steps

1. The ground
2. Hills
3. Two tanks
4. The barrel
5. The game loop
6. Aim
7. Angle and power
8. Fire!
9. Flight
10. Boom
11. Craters
12. Falling tanks
13. Damage
14. Taking turns
15. The computer's shot
16. Hitting a tank
17. Win or lose
18. Wind
19. The computer aims
20. Aim with the mouse
21. Drag and let go
22. The atan2 trap
23. Build it yourself: a trail