Workshop › Angry Birds-style Slingshot › Step 4 of 47

The aim: an angle and a pull

What we are doing

The shot is decided by two numbers: an angle (where the bird will fly) and a pull (how far the band is stretched). We keep them in aim, set up by a reset function.

```js
let aim // { angle, pull }

function reset() {
  aim = { angle: -0.6, pull: 50 }
}

reset()
requestAnimationFrame(loop)
```

What it means

• let aim declares a variable whose value will change; the comment says what it will hold.
• Angles are in radians: half a turn is Math.PI (about 3.14). 0 points right; because y grows downwards, negative angles point up. -0.6 (about 34°) aims up and to the right.
• reset() is called once before the loop starts.

Your turn

1. Under the SLING line leave an empty line and write let aim and the reset function.
2. At the end, write reset() above requestAnimationFrame(loop).

Skills: Game states

← Draw it again and again A bird in the sling →

All steps

1. The sling
2. Sky and ground
3. Draw it again and again
4. The aim: an angle and a pull
5. A bird in the sling
6. Pull the bird back
7. The rubber band
8. Aim with the arrow keys
9. Bodies
10. Launch!
11. Move by the velocity
12. Gravity
13. Land on the ground
14. Aiming or flying
15. An empty sling in flight
16. Gone off the screen
17. Wait for calm
18. The next bird
19. See the path before you shoot
20. From a point to an aim
21. Grab the sling
22. Drag and let go
23. Wood and stone
24. A level as data
25. Push overlapping boxes apart
26. Bounce by mass
27. Every pair meets
28. Friction
29. Smaller steps
30. Hit points
31. Hard hits hurt
32. Things break
33. Pigs
34. Score
35. Show the score
36. Cracks
37. Three birds
38. Count the birds
39. Won or lost
40. The end panel
41. Play again
42. Three levels of data
43. Start any level
44. On to the next level
45. The best score
46. The right words
47. Build it yourself: the yellow bird