d3plus-shape/es/src/geom/simplify.js

Fancy SVG shapes for visualizations

import pointDistanceSquared from "./pointDistanceSquared.js";

/**
    @desc square distance from a point to a segment
    @param {Array} point
    @param {Array} segmentAnchor1
    @param {Array} segmentAnchor2
    @private
*/
function getSqSegDist(p, p1, p2) {
  var x = p1[0],
    y = p1[1];
  var dx = p2[0] - x,
    dy = p2[1] - y;
  if (dx !== 0 || dy !== 0) {
    var t = ((p[0] - x) * dx + (p[1] - y) * dy) / (dx * dx + dy * dy);
    if (t > 1) {
      x = p2[0];
      y = p2[1];
    } else if (t > 0) {
      x += dx * t;
      y += dy * t;
    }
  }
  dx = p[0] - x;
  dy = p[1] - y;
  return dx * dx + dy * dy;
}

/**
    @desc basic distance-based simplification
    @param {Array} polygon
    @param {Number} sqTolerance
    @private
*/
function simplifyRadialDist(poly, sqTolerance) {
  var point,
    prevPoint = poly[0];
  var newPoints = [prevPoint];
  for (var i = 1, len = poly.length; i < len; i++) {
    point = poly[i];
    if (pointDistanceSquared(point, prevPoint) > sqTolerance) {
      newPoints.push(point);
      prevPoint = point;
    }
  }
  if (prevPoint !== point) newPoints.push(point);
  return newPoints;
}

/**
    @param {Array} polygon
    @param {Number} first
    @param {Number} last
    @param {Number} sqTolerance
    @param {Array} simplified
    @private
*/
function simplifyDPStep(poly, first, last, sqTolerance, simplified) {
  var index,
    maxSqDist = sqTolerance;
  for (var i = first + 1; i < last; i++) {
    var sqDist = getSqSegDist(poly[i], poly[first], poly[last]);
    if (sqDist > maxSqDist) {
      index = i;
      maxSqDist = sqDist;
    }
  }
  if (maxSqDist > sqTolerance) {
    if (index - first > 1) simplifyDPStep(poly, first, index, sqTolerance, simplified);
    simplified.push(poly[index]);
    if (last - index > 1) simplifyDPStep(poly, index, last, sqTolerance, simplified);
  }
}

/**
    @desc simplification using Ramer-Douglas-Peucker algorithm
    @param {Array} polygon
    @param {Number} sqTolerance
    @private
*/
function simplifyDouglasPeucker(poly, sqTolerance) {
  var last = poly.length - 1;
  var simplified = [poly[0]];
  simplifyDPStep(poly, 0, last, sqTolerance, simplified);
  simplified.push(poly[last]);
  return simplified;
}

/**
    @function largestRect
    @desc Simplifies the points of a polygon using both the Ramer-Douglas-Peucker algorithm and basic distance-based simplification. Adapted to an ES6 module from the excellent [Simplify.js](http://mourner.github.io/simplify-js/).
    @author Vladimir Agafonkin
    @param {Array} poly An Array of points that represent a polygon.
    @param {Number} [tolerance = 1] Affects the amount of simplification (in the same metric as the point coordinates).
    @param {Boolean} [highestQuality = false] Excludes distance-based preprocessing step which leads to highest quality simplification but runs ~10-20 times slower.

*/
export default (function (poly) {
  var tolerance = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : 1;
  var highestQuality = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : false;
  if (poly.length <= 2) return poly;
  var sqTolerance = tolerance * tolerance;
  poly = highestQuality ? poly : simplifyRadialDist(poly, sqTolerance);
  poly = simplifyDouglasPeucker(poly, sqTolerance);
  return poly;
});