.then(function writeResult (pixels) {
// FIXME find a good format to output
program.output.write(["P3\n# gl.ppm\n", program.width, " ", program.height, "\n255\n"].join(""));
for(var i=0; i<pixels.length; ++i) {
program.output.write(pixels[i] + " ");
}
program.output.end();
})