Adventures in WebGL

Back in October I mentioned that I was looking at learning WebGL. I finally managed to find some time to do it this month and have made some pleasing progress.

My plan was to start off creating a simple 2D framework to replace jaws.js. I’ve been using this framework since I started playing around making games and I really like its simplicity, but I was butting up against its performance. Since it had a load of stuff in it I’m probably never going to use, rolling my own seemed like a good idea.

My first attempt was very disappointing from the performance point of view.

I asked for help. I was doing so very little with my demo that I couldn’t understand why the performance was so poor. I got some pointers and was able to make some changes. Basically, you can’t do lots of buffer\push\draw operations very fast in WebGL. You have to break them down so that you’re buffering a whole load of points into memory then drawing them all at once. I was able to get much better performance by creating a SpriteBucket. drawing ~500 sprites at a time appeared to give me the best balance, giving me >10,000 sprites @ 60fps.

On the whole, I was unprepared for how delicate the balance was between getting reasonable drawing rate and not. I naively thought that WebGL was a super powerhouse of graphics processing and I would only start to have problems when I started trying to do stupid things. I suppose you could argue that plastering 5000+ sprites on the screen at once and redrawing everything constantly is stupid, but my LD30 game had tilemaps and monsters that could have potentially approached this and it didn’t run very well.

With a few obvious tweaks like not bothering to draw stuff off screen (duh!) and only updating vertices and texture coordinates if something has actually changed I saw immediate improvements. The less obvious (to me at the time) stuff, like buffering batches of sprites for a single draw call made the biggest difference.

Introducing Glixl

The end product from my dalliances this month was Glixl. Glixl can create sprite and tile maps from 2D sprite sheets. It goes pretty fast if you pay attention to what’s being drawn, although there are still areas I can improve. My intention is to use this for my games from now on, so I’ll be developing it as I go, adding features that I need. Some things that I still need to work on:

  • Mouse & Touch controls
  • Tilemap path finding
  • Animated tiles

and I need to improve the SpriteBucket object as it has a few things I feel are hacky. Overall though, it does exactly what I want it to do.

I’ve started making a simple game, Dojo Master. to test it too, which is working out quite nicely. So far I only had to add 1 feature to get it working.

Dojo Master.