energy_minimize.js

//  node kernel.js > out.txt; gnuplot -p -e 'plot "out.txt" using 1:2 with points pt 7'

function minimizeEnergy(samples, sampleCount, steps) {
    // energy conservation
    // https://web.archive.org/web/20090422055305/
    // http://www.malmer.nu/index.php/2008-04-11_energy-minimization-is-your-friend/

    for (var step = 0; step < steps; ++step) {
      for (var i = 0; i < sampleCount; ++i) {
        var x = samples[i * 2];
        var y = samples[i * 2 + 1];

        var fx = 0.0;
        var fy = 0.0;
        for (var j = 0; j < sampleCount; ++j) {
          var dX = x - samples[j * 2];
          var dY = y - samples[j * 2 + 1];

          // inverse square
          var lengthSqr = (dX * dX + dY * dY);
          if (lengthSqr > 0.01) {

            var power  = 1.0 / lengthSqr;
            fx += power * dX;
            fy += power * dY;
          }
        }

        var ex = x + fx * 0.001;
        var ey = y + fy * 0.001;

        var len = Math.sqrt(ex * ex + ey * ey);
        if (len > 1.0) {
          ex /= len;
          ey /= len;
        }

        samples[i * 2] = ex;
        samples[i * 2 + 1] = ey;
      }
    }
  }

  function createSsaoKernel(sampleCount) {
    // Random points in disc, biased against center + .
    var samples = new Float32Array(sampleCount * 2);
    for (var i = 0; i < sampleCount; ++i) {
      var theta = i * 2.0 * Math.PI / sampleCount;
      var bias = 0.1;
      var r = bias + Math.random() * (1.0 - bias);
      samples[i * 2] = Math.cos(theta) * r;
      samples[i * 2 + 1] = Math.sin(theta) * r;
    }
    minimizeEnergy(samples, sampleCount, 5);
    for (var i = 0; i < sampleCount; ++i) {
      console.log("" + samples[i * 2] + "\t" + samples[i * 2 + 1]);
    }
    return samples;
  }

createSsaoKernel(32);