1. 5 tips for your
HTML5 games
@ernesto_jimenez
Lead Developer, Six to Start

2. 5 things that
might be helpful
developing your games

3. the game loop

4. GAME LOOP
function updateGame () {
processPlayerInput();
updateGameLogic();
draw();
setTimeout(updateGame, 25);
}

5. GAME LOOP
• Drawing is the most expensive
• Game is locked while running the update
• We are consuming resources

6. you don’t always need
a game loop

7. frame buffering

8. ABOUT FLICKERING
function draw() {
var canvas = document.getElementById('visible-canvas');
var context = canvas.getContext('2d');
context.fillStyle = 'red';
// Draw 200x200 square in x: 0 y: 0
context.fillRect(0, 0, 200, 200);
// Draw 200x200 square in x: 200 y: 200
context.fillRect(0, 0, 200, 200);
}

9. ABOUT FLICKERING
function draw() {
var canvas = document.getElementById('visible-canvas');
var context = canvas.getContext('2d');
context.fillStyle = 'red';
// Draw 200x200 square in x: 0 y: 0
context.fillRect(0, 0, 200, 200);
// Draw 200x200 square in x: 200 y: 200
context.fillRect(0, 0, 200, 200);
}

10. ABOUT FLICKERING
function draw() {
var canvas = document.getElementById('visible-canvas');
var context = canvas.getContext('2d');
context.fillStyle = 'red';
// Draw 200x200 square in x: 0 y: 0
context.fillRect(0, 0, 200, 200);
// Draw 200x200 square in x: 200 y: 200
context.fillRect(0, 0, 200, 200);
}

11. USE TWO CANVAS
off-screen visible

12. 1) DRAW OFF-SCREEN
off-screen visible

13. 2) COPY THE RESULT
off-screen visible

14. RIGHT FRAME BUFFER
function draw() {
var buffer = document.createElement('canvas');
var canvas = document.getElementById('visible-canvas');
buffer.width = canvas.width;
buffer.height = canvas.height;
var buffer_context = buffer.getContext('2d');
var context = canvas.getContext('2d');
buffer_context.fillStyle = 'red';
// Draw ...
context.drawImage(buffer, 0, 0);
}

15. WRONG FRAME BUFFER
function draw() {
var buffer = document.createElement('canvas');
var canvas = document.getElementById('visible-canvas');
buffer.width = canvas.width;
buffer.height = canvas.height;
var buffer_context = buffer.getContext('2d');
var context = canvas.getContext('2d');
buffer_context.fillStyle = 'red';
// Draw ...
var data = buffer_context.getImageData(0, 0, canvas.width,
canvas.height);
context.putImageData(data, 0, 0);
}

16. avg. time for 1,000 frame-buffer operations in Firefox 4.0b7
right frame buffer wrong frame buffer
7,000ms
6,300ms
5,600ms
4,900ms
4,200ms
3,500ms
2,800ms
2,100ms
1,400ms
700ms
0ms
plain color

17. frame buffer is not
always useful right now
Browsers are repainting the canvas after your JS

18. expensive drawing

19. getImageData
&
putImageData

20. avg. time for 1,000 fillRect in Firefox 4.0b7
fillRect 100x100px fillRect 500x500px
4,000ms
3,500ms
3,000ms
2,500ms
2,000ms
1,500ms
1,000ms
500ms
0ms
plain color 3 stops linear gradient blurred shadow

21. fillText is cool
but it is expensive

22. think outside of the
canvas

23. 1 GAME != 1 CANVAS

24. combine different
canvas to produce a
single screen

25. images from Belén Albeza (@ladybenko)

26. images from Belén Albeza (@ladybenko)

27. dirty rectangles

28. redraw only those areas
that have changed

29. images from Belén Albeza (@ladybenko)

30. images from Belén Albeza (@ladybenko)

32. HIGH
PERFORMANCE
JAVASCRIPT
Nicholas C. Zakas
http://oreilly.com/catalog/9780596802806