Workshop › Klondike Solitaire › Step 29 of 40

Follow the pointer

What we are doing

While a card is held, every pointer move updates drag.x and drag.y. A move of more than 4 pixels marks it as a real drag; a finger always wobbles a little, and that should still be a tap.

```js
canvas.addEventListener('pointermove', (event) => {
  if (!drag) return
  const p = toCanvas(event)
  if (Math.hypot(p.x - drag.x, p.y - drag.y) > 4) drag.moved = true
  drag.x = p.x
  drag.y = p.y
})
```

What it means

• Moves without a held card are ignored.
• Math.hypot(a, b) is the length of the line with sides a and b (Pythagoras): the distance between the last point and the new one.
• Then the new position is stored.

Your turn

Under the pointerdown listener, leave an empty line and write the pointermove listener.

Skills: Keyboard and mouse input

← Where did you grab it? Draw the held cards at the pointer →

All steps

1. The green table
2. Draw one card
3. The face of a card
4. Red and black
5. A deck of 52
6. Shuffle
7. Piles in one object
8. Deal the seven columns
9. A place for every pile
10. Put the piles on the table
11. Fan out the columns
12. Outlines for empty places
13. Turn over a card
14. Space turns a card
15. Go through the stock again
16. What is under the pointer?
17. Hitting a card in a column
18. Tap the stock
19. Rule 1: building a column
20. Rule 2: building a foundation
21. Move cards by the rules
22. Turn over the uncovered card
23. Find where a card goes
24. Pick up a card
25. Tap to move
26. A move counter
27. Count the moves
28. Where did you grab it?
29. Follow the pointer
30. Draw the held cards at the pointer
31. Drop it where you want
32. Drop a king into an empty column
33. A clock
34. Winning
35. You won!
36. A new game
37. The best time
38. Snapshots of the table
39. Undo
40. Build it yourself: finish by itself