Workshop › Lunar Lander › Step 19 of 31

Landing or crashing

What we are doing

A touch is a landing only if everything is right: both feet on the pad, falling slowly, hardly drifting and nearly upright. The limits live in one object, SAFE.

```js
const SAFE = { vy: 1.2, vx: 0.6, angle: 0.2 } // the most a landing may have

function touchdown() {
  const onPad = lander.x - FEET >= pad.x1 && lander.x + FEET <= pad.x2
  const gentle = lander.vy <= SAFE.vy && Math.abs(lander.vx) <= SAFE.vx && Math.abs(lander.angle) <= SAFE.angle
  if (onPad && gentle) {
    state = 'landed'
    lander.y = pad.y - 10
    return
  }
  state = 'crashed'
}
```

What it means

• onPad: the left foot is right of the pad's start and the right foot left of its end.
• gentle: the falling speed, the sideways speed and the tilt are all within SAFE. Math.abs ignores the sign, so drifting left or right (and tilting either way) count the same.
• A landing sets the lander exactly on the pad; anything else is a crash.

Your turn

1. Above const FEET write the SAFE constant.
2. Replace the body of touchdown with the new lines.

Skills: Collision detection, Game states

← Touch controls Fly again →

All steps

1. Random hills
2. Draw the hills
3. A landing pad
4. The height at any x
5. The lander
6. Draw it around its own middle
7. Two feet
8. The game loop
9. Moon gravity
10. Around the sides
11. Flying or not
12. Touching the ground
13. Remember held keys
14. Tilt
15. The engine
16. A flickering flame
17. Fuel
18. Touch controls
19. Landing or crashing
20. Fly again
21. Landed or crashed?
22. Readouts
23. Levels
24. Score
25. Next level or new game
26. A narrower pad
27. A high score
28. Burst into pieces
29. Pieces fall and fade
30. Draw the wreck
31. Build it yourself: wind