Workshop › Mario-style Platformer › Step 26 of 37

Enemies that walk

What we are doing

Here the work on moveX and moveY pays off: they take any body. An enemy walks one pixel a frame in its direction, turns around when moveX reports a wall, and falls and lands with the same gravity as the player.

```js
function updateEnemy(enemy) {
  enemy.vx = enemy.dir
  if (moveX(enemy)) enemy.dir = -enemy.dir
  enemy.vy = Math.min(MAX_FALL, enemy.vy + GRAVITY)
  moveY(enemy)
}

  for (const enemy of enemies) updateEnemy(enemy)
```

What it means

• vx = dir: one pixel per frame left or right.
• moveX returns true at a wall; then dir = -dir turns the enemy around.
• Gravity and moveY exactly as for the player.
• update calls it for every enemy, after the player.

Your turn

1. Above function update() { write updateEnemy, with an empty line after it.
2. In update, under updatePlayer(), write the enemy loop.

Skills: Velocity and gravity, Functions

← Enemies Do not walk off ledges →

All steps

1. The sky
2. A level made of text
3. Draw the tiles
4. What is solid?
5. Is a box touching anything?
6. Find the start
7. Draw the player
8. Gravity
9. Landing on tiles
10. Which keys are held?
11. Speed up
12. Friction
13. Walls
14. Jump
15. Bump your head
16. Short hops
17. A few frames of grace
18. Coyote time
19. A camera that follows
20. Stop at the ends
21. Draw only what is on screen
22. Coins
23. Collect them
24. Count, and screen versus world
25. Enemies
26. Enemies that walk
27. Do not walk off ledges
28. Lives and a fresh start
29. Falling into a pit
30. Enemies hurt
31. Stomp!
32. Squashed enemies are gone
33. Game over
34. Play again
35. The flag
36. Reach the flag
37. Build it yourself: jump buffering