Function d3_geo_resample

explainshell/web/static/js/d3.v3.js:2807–2874

(project)

    return compose;
  }
  function d3_geo_resample(project) {
    var δ2 = .5, maxDepth = 16;
    function resample(stream) {
      var λ0, x0, y0, a0, b0, c0;
      var resample = {
        point: point,
        lineStart: lineStart,
        lineEnd: lineEnd,
        polygonStart: function() {
          stream.polygonStart();
          resample.lineStart = polygonLineStart;
        },
        polygonEnd: function() {
          stream.polygonEnd();
          resample.lineStart = lineStart;
        }
      };
      function point(x, y) {
        x = project(x, y);
        stream.point(x[0], x[1]);
      }
      function lineStart() {
        x0 = NaN;
        resample.point = linePoint;
        stream.lineStart();
      }
      function linePoint(λ, φ) {
        var c = d3_geo_cartesian([ λ, φ ]), p = project(λ, φ);
        resampleLineTo(x0, y0, λ0, a0, b0, c0, x0 = p[0], y0 = p[1], λ0 = λ, a0 = c[0], b0 = c[1], c0 = c[2], maxDepth, stream);
        stream.point(x0, y0);
      }
      function lineEnd() {
        resample.point = point;
        stream.lineEnd();
      }
      function polygonLineStart() {
        var λ00, φ00, x00, y00, a00, b00, c00;
        lineStart();
        resample.point = function(λ, φ) {
          linePoint(λ00 = λ, φ00 = φ), x00 = x0, y00 = y0, a00 = a0, b00 = b0, c00 = c0;
          resample.point = linePoint;
        };
        resample.lineEnd = function() {
          resampleLineTo(x0, y0, λ0, a0, b0, c0, x00, y00, λ00, a00, b00, c00, maxDepth, stream);
          resample.lineEnd = lineEnd;
          lineEnd();
        };
      }
      return resample;
    }
    function resampleLineTo(x0, y0, λ0, a0, b0, c0, x1, y1, λ1, a1, b1, c1, depth, stream) {
      var dx = x1 - x0, dy = y1 - y0, d2 = dx * dx + dy * dy;
      if (d2 > 4 * δ2 && depth--) {
        var a = a0 + a1, b = b0 + b1, c = c0 + c1, m = Math.sqrt(a * a + b * b + c * c), φ2 = Math.asin(c /= m), λ2 = Math.abs(Math.abs(c) - 1) < ε ? (λ0 + λ1) / 2 : Math.atan2(b, a), p = project(λ2, φ2), x2 = p[0], y2 = p[1], dx2 = x2 - x0, dy2 = y2 - y0, dz = dy * dx2 - dx * dy2;
        if (dz * dz / d2 > δ2 || Math.abs((dx * dx2 + dy * dy2) / d2 - .5) > .3) {
          resampleLineTo(x0, y0, λ0, a0, b0, c0, x2, y2, λ2, a /= m, b /= m, c, depth, stream);
          stream.point(x2, y2);
          resampleLineTo(x2, y2, λ2, a, b, c, x1, y1, λ1, a1, b1, c1, depth, stream);