var n = 20, // number of layers

    m = 200, // number of samples per layer

    data0 = d3.layout.stack().offset("wiggle")(stream_layers(n, m)),

    data1 = d3.layout.stack().offset("wiggle")(stream_layers(n, m)),

    color = d3.interpolateRgb("#aad", "#556");

var w = 960,

    h = 500,

    mx = m - 1,

    my = d3.max(data0.concat(data1), function(d) {

      return d3.max(d, function(d) {

        return d.y0 + d.y;

      });

    });

var area = d3.svg.area()

    .x(function(d) { return d.x * w / mx; })

    .y0(function(d) { return h - d.y0 * h / my; })

    .y1(function(d) { return h - (d.y + d.y0) * h / my; });

var vis = d3.select("#chart")

  .append("svg:svg")

    .attr("width", w)

    .attr("height", h);

vis.selectAll("path")

    .data(data0)

  .enter().append("svg:path")

    .style("fill", function() { return color(Math.random()); })

    .attr("d", area);

function transition() {

  d3.selectAll("path")

      .data(function() {

        var d = data1;

        data1 = data0;

        return data0 = d;

      })

    .transition()

      .duration(2500)

      .attr("d", area);

}