JavaScript implementation of S3TC algorithm. Only DXT1 w/o alpha implemented. The implementation is suffiently fast to be used as an online compressor of small images (~10-20ms for a 256 to 256 pixels).
Let's assume that we already have WebGL context gl and an CommonJS module system.
Here what we can do to create a compressed texture:
var s3tcExt = gl.getExtension('WEBGL_compressed_texture_s3tc') ||
gl.getExtension('MOZ_WEBGL_compressed_texture_s3tc') ||
gl.getExtension('WEBKIT_WEBGL_compressed_texture_s3tc');
console.assert(s3tcExt, 'Oops! No S3TC extension.');
gl.bindTexture(gl.TEXTURE_2D, gl.createTexture());
gl.compressedTexImage2D(
gl.TEXTURE_2D,
0,
s3tcExt.COMPRESSED_RGBA_S3TC_DXT1_EXT,
width,
height,
0,
require('dxt1').compress(canvasWithTexture.getImageData(0, 0, width, height))
);