WebGL Experiments: Texture Compression

Lilli Thompson from Google asked us how we were doing texture decompression in the pixel shaders and what algorithm we were using. We thought we would share our answer…

Texture compression was a bit of journey – as no one at Illyriad had ever implemented anything in 3d before; to us texture compression was mostly a tick box on a graphics card.

It started when we found out our 90MB of jpegs expanded to 2GB of on-board memory and we were worried we’d made a terrible mistake, as this was certainly beyond the possibilities of low-end hardware! Half of it this was due to Three.js keeping a reference to the image and the image also being copied to the GPU process – so essentially the required texture memory doubled.

Dropping the reference Three.js held after the texture was bound to WebGL resolved this. I’m not sure how this will play out with context lost events – as I assume we will have lost the texture at that point – but local caching in the file system and reloading may help with recreating them at speed.

With 1GB of memory remaining we were faced with three choices – either deciding what were were trying to do wasn’t possible; reducing the texture sizes and losing fidelity or trying to implement texture de-compression in the shader. Naturally we opted for the last.

We were originally planning to use 24bit S3TC/DX1; however this proved overly complex in the time we had available as the pixel shaders have no integer masking or bitshifts and everything needs to be worked in floats. The wonders we could unleash with binary operators and type casting (not conversion) – but I digress…

In the end we compromised on 256 colour pallettized textures (using AMD’s The Compressonator to generate P8 .DDS textures). This reduced the texture to one byte per pixel – not as small or high colour as DX1 – but already 4 times smaller than our original uncompressed RGBA textures.

It took a while to divine the file format; which we load via XMLHttpRequest into an arraybuffer. The files have 128 bytes of header which we ignore, followed by the 256×4 byte palette which we load into a lookup table texture RGBA. The rest we load into a Luminance texture. Both textures need to use NearestFilter sampling and not use mipmapping to be interpreted sensibly.

We have created our own compressed texture loaders – the colour texture loader looks a little like this:

[code lang=”javascript”]
Illyriad.TextureCompColorLoader = function (path, width, height, uniforms) {
var texture = new THREE.DataTexture(0, 1, 1, THREE.LuminanceFormat,
(new THREE.UVMapping()), THREE.RepeatWrapping, THREE.RepeatWrapping,
THREE.NearestFilter, THREE.NearestFilter);

var request = new XMLHttpRequest();
request.open("GET", path, true);
request.responseType = "arraybuffer";

// Decode asynchronously
request.onload = function () {
if (request.status == 200) {
var imageDataLength = request.response.byteLength – width * height;
uniforms.tColorLUT.texture = new THREE.DataTexture(
new Uint8Array(request.response, 128, 256 * 4),
256, 1, THREE.RGBAFormat, (new THREE.UVMapping()),
THREE.ClampToEdgeWrapping, THREE.ClampToEdgeWrapping,
THREE.NearestFilter, THREE.NearestFilter);
uniforms.tColorLUT.texture.needsUpdate = true;
texture.image = { data: new Uint8Array(request.response, imageDataLength),
width: width, height: height };
texture.needsUpdate = true;
return texture;

When we first did the decompression in the pixel shader, it was very blocky as we had turned off filtering to read the correct values from the texture. To get around this we had to add our own bilinearSample function to do the blending for us. In this function it uses the diffuse texture with the colour look up table and using the texture size and texture pixel interval samples the surrounding pixels. The other gotcha is that the lookup texture is in BGRA format so the colours need to be swizzeled. This makes that portion of the shader look like this:

uniform sampler2D tDiffuse;
uniform sampler2D tColorLUT;

uniform float uTextInterval;
uniform float uTextSize;

vec3 bilinearSample(vec2 uv, sampler2D indexT, sampler2D LUT)
vec2 tlLUT = texture2D(indexT, uv ).xx;
vec2 trLUT = texture2D(indexT, uv + vec2(uTextInterval, 0)).xx ;
vec2 blLUT = texture2D(indexT, uv + vec2(0, uTextInterval)).xx;
vec2 brLUT = texture2D(indexT, uv + vec2(uTextInterval , uTextInterval)).xx;

vec2 f = fract( uv.xy * uTextSize );
vec4 tl = texture2D(LUT, tlLUT).zyxw;
vec4 tr = texture2D(LUT, trLUT).zyxw;
vec4 bl = texture2D(LUT, blLUT).zyxw;
vec4 br = texture2D(LUT, brLUT).zyxw;
vec4 tA = mix( tl, tr, f.x );
vec4 tB = mix( bl, br, f.x );
return mix( tA, tB, f.y ).xyz;

void main()
vec4 colour = vec4(bilinearSample(vUv,tDiffuse,tColorLUT),1.0);


This performs fairly well; and certainly better than when your computer feels some virtual memory is required because you are using too much! However, I’m sure on-board graphics card decompression should be swifter and hopefully open up the more complex S3TC/DX1-5 compression formats.

There is a major downside however with decompressing this way in the pixel shader. You have to turn off mipmapping! Not only does turning off mipmapping cause a performance hit as you always have to read the full-size textures – but more importantly it doesn’t look good. In fact in the demo – we had to use full-size textures for the grass so we could apply mipmapping as otherwise in the distance it was a wall of static!

Unfortunately, as far as I’m aware, WebGL while you can create mipmaps with generateMipmap – you can’t supply your own. Again, real compressed textures should help here.

EDIT: Benoit Jacob has pointed out this is possible by passing a non-zero ‘level’ parameter to texImage2D – one to look into.

Some caveats on the demo:

  • Obviously even 90MB of jpeg textures is far too much – the production version will be substantially smaller, as we are being a bit smarter on how we will be using them.
  • This has been a learning process both for us and Quantic Arts (who are used to boxed set games).
  • This was a tester to see the upper limits of what we can do in WebGL, so we haven’t been focusing on optimization yet.
  • We will be reworking the obj models to reduce their download size substantially.
  • The way the game works is that no one player will need all the textures at once (the time between queuing a building and it’s actual appearance in the game allows us to download the models/texture)

So the actual game requirements will be much much lower.

WebGL Experiments: Illyriad’s 3d Town

What can WebGL do? Can it do what we want? We were wondering.. and so decided to put it to the test…

To test the upper bounds of WebGL we put together a rough and ready demo [caution – it’s bandwidth hungry].  It’s very rough, not optimized and currently only runs on Chrome [working in all browsers that support WebGL is our priority]; but that’s kind of the point – its a technology tester to ensure we weren’t making a mistake.

The results speak of themselves – it definitely proves itself!  Sure it needs a bit more polish, but we are now confident that the actual in-game libraries we are building have a lot of head room to use. Below are a couple screenshots of the town during the day:

And another at night:

Of course there were many trials along the way and things that didn’t quite work as we’d planned as can seen below:


We learnt the importance of GPU compressed textures and had to write a pixel shader decompressor of our own, as WebGL doesn’t currently support them natively – but with a cost.  The loss of mip-maping this causes it can clearly be seen; and we will have to work around this if they are not supported soon.

Overall we are very pleased with the result, which you can check out here.  Remember to press space to unlock your mouse to look around – if you aren’t fond of reading on-screen instructions 😉

Naturally this is just a taster of what we have waiting in the wings. We’ll look to provide some follow-up blog posts about the techniques and tools being used in this early experiment including:

  • Web Audio API
  • Pixel shader texture decompression
  • Deferred shading

3rd Party Libraries in use

Illyriad: HTML5 WebGL Preview 2

We thought we’d up the game on the last demo and show a bit of lighting and animation.

A high level flour mill from Illyriad seemed an obvious choice!

Again this is purely HTML5 using the WebGL canvas and JavaScript; no plugins were used. We use mrdoob’s excellent Three.js library:


We’ve included the full browser window in this recording to show that it is in fact running in a Chrome browser window. While it happily runs at 1080p, we’ve had to record at a much lower resolution as the screen capture utility slows everything down… Alas.

Illyriad: HTML5 WebGL Preview

We’ve done a bit of bloging about the “now”, but what about the future?

Well here at Illyriad we’ve been experimenting with WebGL and I can tell you we are impressed with how its shaping up.

Here’s a little taster of what we’ve been trying:


Its slightly shaky – but that’s my mouse movement not any lag from WebGL. Looks like I might never be a brain surgeon… haha