// consistent overplotting
var round = start / context.step() & 1
    ? cubism_comparisonRoundOdd
    : cubism_comparisonRoundEven;

// positive changes
canvas.fillStyle = colors[2];
for (var i = 0, n = width; i < n; ++i) {
  var y0 = scale(primary_.valueAt(i)),
      y1 = scale(secondary_.valueAt(i));
  if (y0 < y1) canvas.fillRect(round(i), y0, 1, y1 - y0);
}

// negative changes
canvas.fillStyle = colors[0];
for (i = 0; i < n; ++i) {
  var y0 = scale(primary_.valueAt(i)),
      y1 = scale(secondary_.valueAt(i));
  if (y0 > y1) canvas.fillRect(round(i), y1, 1, y0 - y1);
}

// positive values
canvas.fillStyle = colors[3];
for (i = 0; i < n; ++i) {
  var y0 = scale(primary_.valueAt(i)),
      y1 = scale(secondary_.valueAt(i));
  if (y0 <= y1) canvas.fillRect(round(i), y0, 1, strokeWidth);
}

// negative values
canvas.fillStyle = colors[1];
for (i = 0; i < n; ++i) {
  var y0 = scale(primary_.valueAt(i)),
      y1 = scale(secondary_.valueAt(i));
  if (y0 > y1) canvas.fillRect(round(i), y0 - strokeWidth, 1, strokeWidth);
}

canvas.restore();
}