source: Dev/trunk/d3/src/scale/linear.js @ 76

d3.scale.linear = function() {
  var domain = [0, 1],
      range = [0, 1],
      interpolate = d3.interpolate,
      clamp = false,
      output,
      input;

  function rescale() {
    var linear = domain.length == 2 ? d3_scale_bilinear : d3_scale_polylinear,
        uninterpolate = clamp ? d3_uninterpolateClamp : d3_uninterpolateNumber;
    output = linear(domain, range, uninterpolate, interpolate);
    input = linear(range, domain, uninterpolate, d3.interpolate);
    return scale;
  }

  function scale(x) {
    return output(x);
  }

  // Note: requires range is coercible to number!
  scale.invert = function(y) {
    return input(y);
  };

  scale.domain = function(x) {
    if (!arguments.length) return domain;
    domain = x.map(Number);
    return rescale();
  };

  scale.range = function(x) {
    if (!arguments.length) return range;
    range = x;
    return rescale();
  };

  scale.rangeRound = function(x) {
    return scale.range(x).interpolate(d3.interpolateRound);
  };

  scale.clamp = function(x) {
    if (!arguments.length) return clamp;
    clamp = x;
    return rescale();
  };

  scale.interpolate = function(x) {
    if (!arguments.length) return interpolate;
    interpolate = x;
    return rescale();
  };

  scale.ticks = function(m) {
    return d3_scale_linearTicks(domain, m);
  };

  scale.tickFormat = function(m) {
    return d3_scale_linearTickFormat(domain, m);
  };

  scale.nice = function() {
    d3_scale_nice(domain, d3_scale_linearNice);
    return rescale();
  };

  return rescale();
};

function d3_scale_linearRebind(scale, linear) {
  scale.range = d3.rebind(scale, linear.range);
  scale.rangeRound = d3.rebind(scale, linear.rangeRound);
  scale.interpolate = d3.rebind(scale, linear.interpolate);
  scale.clamp = d3.rebind(scale, linear.clamp);
  return scale;
}

function d3_scale_linearNice(dx) {
  dx = Math.pow(10, Math.round(Math.log(dx) / Math.LN10) - 1);
  return {
    floor: function(x) { return Math.floor(x / dx) * dx; },
    ceil: function(x) { return Math.ceil(x / dx) * dx; }
  };
}

// TODO Dates? Ugh.
function d3_scale_linearTickRange(domain, m) {
  var extent = d3_scaleExtent(domain),
      span = extent[1] - extent[0],
      step = Math.pow(10, Math.floor(Math.log(span / m) / Math.LN10)),
      err = m / span * step;

  // Filter ticks to get closer to the desired count.
  if (err <= .15) step *= 10;
  else if (err <= .35) step *= 5;
  else if (err <= .75) step *= 2;

  // Round start and stop values to step interval.
  extent[0] = Math.ceil(extent[0] / step) * step;
  extent[1] = Math.floor(extent[1] / step) * step + step * .5; // inclusive
  extent[2] = step;
  return extent;
}

function d3_scale_linearTicks(domain, m) {
  return d3.range.apply(d3, d3_scale_linearTickRange(domain, m));
}

function d3_scale_linearTickFormat(domain, m) {
  return d3.format(",." + Math.max(0, -Math.floor(Math.log(d3_scale_linearTickRange(domain, m)[2]) / Math.LN10 + .01)) + "f");
}