Workshop › Conway's Game of Life › Step 27 of 32

Patterns from text

What we are doing

Famous patterns are shared as text: one line per row, O for a live cell and . for a dead one. stamp copies such a picture onto the grid.

```js
// Copy a text pattern onto the grid with its top left corner at (row, col).
function stamp(pattern, row, col) {
  pattern.forEach((line, r) => {
    for (let c = 0; c < line.length; c++) if (line[c] === 'O') grid[(row + r) % ROWS][(col + c) % COLS] = 1
  })
}
```

What it means

• pattern.forEach((line, r) => ...) runs once for each line of text; r is the line's number.
• A text works like a list of letters: line[c] is the letter at c, line.length how many letters there are.
• Every 'O' sets the cell (row + r, col + c), wrapped with % like the rest of this world.

Your turn

Write stamp under clear, after an empty line.

Skills: Arrays and objects, Loops

← Drag to paint The glider gun →

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