Workshop › Pong › Step 6 of 26

A function that draws

What we are doing

A game redraws its picture many times a second. We put the drawing lines in a function named draw, so one word repaints everything.

```js
function draw() {
  ctx.fillStyle = 'black'
  ctx.fillRect(0, 0, canvas.width, canvas.height)

  ctx.fillStyle = 'white'
  for (let y = 0; y < canvas.height; y += 30) {
    ctx.fillRect(canvas.width / 2 - 2, y, 4, 15)
  }

  ctx.fillRect(left.x, left.y, PADDLE_W, PADDLE_H)
  ctx.fillRect(right.x, right.y, PADDLE_W, PADDLE_H)
}

draw()
```

What it means

• function draw() { ... } defines the recipe; it does not run yet.
• The body is indented by two spaces.
• draw() with parentheses runs it. It paints the court black first, which wipes the old picture.

Your turn

Wrap all the drawing lines in function draw() { ... } (indent them by two spaces) and call draw() after it.

Skills: Functions

← Two paddles The game loop →

All steps

1. Get the canvas and the pen
2. A black court
3. One dash of the net
4. The whole net
5. Two paddles
6. A function that draws
7. The game loop
8. Remember held keys
9. Move the paddles
10. Stay on the court
11. The ball
12. The ball moves
13. Bounce off the top and bottom
14. Does the ball touch a paddle?
15. The paddles hit back
16. Serve again
17. Keep the score
18. Show the score
19. First to five
20. Who won?
21. Play again
22. Aim with the paddle
23. Faster every hit
24. A computer opponent
25. One player or two
26. Build it yourself: a serve pause