Workshop › Conway's Game of Life › Step 31 of 32

Tap the buttons

What we are doing

A press at or below BAR_Y is on a button: Math.floor(point.x / BUTTON_W) finds which one, and we call the same press as the keyboard.

```js
canvas.addEventListener('pointerdown', (event) => {
  const point = toCanvas(event)
  if (point.y >= BAR_Y) {
    press(BUTTONS[Math.floor(point.x / BUTTON_W)])
    return
  }
  const cell = cellAt(point)
  if (!cell) return
```

What it means

• The point is computed once and kept in point.
• At or below BAR_Y, Math.floor(point.x / BUTTON_W) is the button's number: x = 150 gives 1, 'Step'. We press it and return, so no cell is painted.
• Otherwise cellAt(point) works as before.

Your turn

In the pointerdown listener, replace the line const cell = cellAt(toCanvas(event)) with the new lines.

Skills: Keyboard and mouse input

← Buttons on the screen Build it yourself: a world at rest →

All steps

1. The board
2. Measure the grid
3. One living cell
4. A function that draws
5. The world in memory
6. Draw every living cell
7. A random soup
8. Count the neighbours
9. Four rules
10. Draw again and again
11. Next generation with N
12. Count the generations
13. Show the generation
14. A world without edges
15. Count the living
16. A generation every few frames
17. Let it live
18. Running or not
19. One place for the buttons
20. Space to play, N to step
21. Clear and shuffle
22. Where is the pointer?
23. Which cell?
24. Click a cell
25. Paint or erase?
26. Drag to paint
27. Patterns from text
28. The glider gun
29. Fire the gun
30. Buttons on the screen
31. Tap the buttons
32. Build it yourself: a world at rest