Tuesday, September 18, 2012

js13kgames and Voxel Shooter

I knew I had to take part in js13kgames - A competition to write Javascript games less than 13KB when zipped. I used HTML5 canvas for the last two of the last three game projects I worked on and was increasingly identifying myself as a HTML5 game programmer. However a visit back to India and the work on Mario Ball had left very little time for me to actually work on my 13KB game.

At 13KB I had decided to have some sort of procedural generation for the elements of the game. I also wanted to explore the Web Audio API for the sound. However I was having a very hard time trying to come up with a concrete idea for the game. My very first idea was a weird fighting game where the player's form and powers were determined by a random combination of 3 elements - Rectangles, Circles and Bezier curves. The player and enemies basically looked like modern art pictures. I wasn't sure whether I was going too weird with this one. Some of the denizens of this unfinished game:

Then this entry came out on js13kgames - 13th Knight. It was a fully textured 3D world in WebGL in under 13KB! And it had awesome looking trees!! I wanted to make a WebGL game now. I always wanted to learn WebGL but hadn't looked closely into it it before. I had started looking at three.js for 7dfps but never got the time to do anything beyond a sphere moving on plane. This time around three.js wasn't going to be an option because no external libraries were allowed and three.js would not fit into 13KB (I later learnt somebody else had managed to get a subset of three.js working in their 13KB game - Mindless).

So not exactly knowing what I'm going to build I started with the WebGL lessons at for the basic template for a WebGL program. I played around with it till I was able to draw a flat colored cube with directional lighting. There were 5 days till the competition ended and I had to come up with something quick. Then it struck me - I will just redraw the cubes a lot of times to create a Voxel engine! (Being completely ignorant of the issues before starting a project is sometimes a good thing). I was missing a good flying game these days and I thought I will do a flying game where you shoot enemies on the ground - Voxel Shooter!!

I generated the terrain using some random combination of sin curves. I copied a small subset of the glMatrix library for the matrix operations. And I happily went about drawing cubes over and over again - One drawElements call per cube. I could reach up to 50 x 20 array of cubes before the rendering became too slow. I tried removing faces from the cubes that are hidden behind other cubes - A small increase in the frame rate but nothing great. I tried some cheating like increasing the size of each cube so that I can get away with a smaller number of cubes. Nope - the map was still too small. I banged my head trying to figure out a frustum culling method but it just involved too much Math to be figured out in a small amount of time. Also the far plane was going to be too near and field of view was going to be too narrow if I can display only 1000 cubes. I just had to figure out a way to improve performance first.

Then I came across this - Google I/O 2011 : WebGL Techniques and Performance. I had basically made all the mistakes mentioned in the talk. First and foremost I was switching too much context for every vertex - Even the uniforms that were common to all vertices like lighting and camera and projection matrices. I got a substantial boost when I fixed this issue but still not going to allow the 256 x 256 map size I was aiming for. The next thing was to reduce the number of GL draw calls by combining many cubes into one giant mesh. This one I had some problem getting my head around because I hadn't understood the concept of attributes properly. Then I saw how I could augment the vertex data by putting its world position as an attribute and I could draw the entire terrain with a single drawArrays call - And BAM! Now everything was running smoothly at 19fps (yeah. Much better than 7 fps) for an entire map of 256 x 256.

Everything from here on was mostly polishing. I worked a lot on the camera - I was using the LookAt matrix but couldn't figure out how to roll and I wanted the camera to roll on turning. After scourging the internet found a simple method to just pre-multiply the LookAt matrix with a roll matrix.  I didn't like the way you could lose your bearing if you looked right up. So I added some clouds(All clouds drawn with a single GL draw call), filled the surrounding areas with water and added a wrap around if you strayed too far from the island. I added some cubes to represent the enemies (all drawn with a single call). I spent quite a bit of time overlaying a 2D canvas to represent the minimap so that you would knew where your enemies were. I tried adding bullets to shoot down the enemies with the basic physics handled right in the shader but that wouldn't work - I just had to give up on it. (Did you wonder why it was called Voxel Shooter but there is no shooting? :) I spent the whole night before the competition deadline at 7AM adding these things and then before I realized it was time to submit!

I was very dejected that I didn't complete the game and I was too near to the deadline. You just flew around doing pretty much nothing. You couldn't even crash into anything. Staying awake for the whole night was a complete waste of my time. And then out of sheer desperation I thought I will just add a simple check for crashing into the terrain and that would be the game - Avoid crashing into anything. I was testing it and I kept going through the enemies. I thought I should add collision detection with the enemies as well. I added that and then I realized instead of treating crashing into enemies as a failure, that could be the whole point of the game!! I quickly added a score for picking up the red cube (no longer the enemy!) and increase the speed of the game every time you finished a batch of them. I submitted this new version and was smugly happy with my own crisis handling. Next time I should just give myself more time to avoid such things.

The next day playing through the other entries of the js13kgames and I liked many of them. It was interesting to see the methods they used to keep the size down. The most amazing thing I learnt about was jsfxr - A simple sound effects generator without having to store audio in huge audio files. I am definitely going to use this more in my upcoming projects and in the future versions of Voxel Shooter.

Some people seemed to like Voxel Shooter and it was really cool that picked it - Even Cheezbruger picked it for their Lunch leisure  -! Some were amazed it was done within 13KB but I should mention that my game was very simple - it just does the same thing a lot of times and I didn't spend any time trying to reduce the size.

The initial reaction from people has given me encouragement to keep working on the game and I think I will make it into a full fledged game in the future. Lots of ideas flying in my mind now - Sounds, bigger worlds, flying enemies, improved shading, shadows, water, lava, gamepad support, multiplayer, levels, missions... But now I will automatically think of one more thing - How small can I keep the code and assets?

And to end it all here is a video from my awesome friend Brian who scored 148 in Voxel Shooter! Can you beat that?!!

1 comment:

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