Workshop › Flappy-style Bird › Step 7 of 30

Gravity

What we are doing

A real fall starts slowly and speeds up. We give the bird a velocity vy, and gravity adds a little to it every frame. Then the bird moves by its velocity.

```js
const GRAVITY = 0.5 // added to the bird's speed every frame

let bird = { x: 100, y: 300, vy: 0, r: 14 }

function update() {
  bird.vy += GRAVITY
  bird.y += bird.vy
}
```

What it means

• GRAVITY is how much the speed grows each frame. Names in capitals are settings that never change.
• vy: 0: the bird starts still.
• First the speed grows, then the bird moves by the speed: 0.5 px, then 1, then 1.5... a smooth, speeding-up fall.

Your turn

1. Under const ctx = ..., leave an empty line and write the GRAVITY line.
2. Add vy: 0, to bird, after y: 300,.
3. In update, replace bird.y += 2 with the two new lines.

Skills: Velocity and gravity

← The game loop A flap →

All steps

1. Get the canvas and the pen
2. Paint the sky
3. Draw the bird
4. A function that draws
5. A function that moves
6. The game loop
7. Gravity
8. A flap
9. Space, Up arrow or a tap
10. Wait for the first flap
11. The ground and the sky
12. Tell the player
13. A pipe as data
14. Draw the pipes
15. The world moves, not the bird
16. A new pipe at a random height
17. A pipe every 90 frames
18. Remove the pipes you passed
19. Is the bird level with a pipe?
20. Through the opening
21. Score each pipe once
22. Show the score
23. A function for a fresh start
24. Try again
25. One place where the game ends
26. Remember the best score
27. Show the best score
28. The same speed on every screen
29. No catching up after a pause
30. Build it yourself: a medal