Apply linear interpolation when incrementing the grid?

[mbostock]

Currently we round data points to the nearest grid point before blurring. It would probably be better to apply linear interpolation to a 2×2 grid to the nearest grid points to the data point instead, something like this:

data.forEach(function(d, i, data) {
  var xi = (x(d, i, data) + o) * Math.pow(2, -k),
      yi = (y(d, i, data) + o) * Math.pow(2, -k);
  if (xi >= 0 && xi < n - 1 && yi >= 0 && yi < m - 1) {
    var x0 = Math.floor(xi),
        y0 = Math.floor(yi),
        xt = xi - x0,
        yt = yi - y0;
    values0[x0 + y0 * n] += (1 - xt) * (1 - yt);
    values0[x0 + 1 + y0 * n] += xt * (1 - yt);
    values0[x0 + 1 + (y0 + 1) * n] += xt * yt;
    values0[x0 + (y0 + 1) * n] += (1 - xt) * yt;
  }
});

[mbostock]

Apparently this is called linear binning:

Linear binning is a slight tweak to regular binning where if the grid points x and z surround the data point y, then (z−y)/(z−x) mass is distributed to the grid point at x, and (y − x)/(z − x) to the point at z.