@orca-fe/painter/es/pathSimplify.js

Konva Painter

/**
 * square distance between 2 points
 * @param {[number, number]} p1
 * @param {[number, number]} p2
 * @returns {number}
 */
function getSqDist(p1, p2) {
  var dx = p1[0] - p2[0];
  var dy = p1[1] - p2[1];
  return dx * dx + dy * dy;
}

/**
 * square distance from a point to a segment
 *
 * @param {[number, number]} p
 * @param {[number, number]} p1
 * @param {[number, number]} p2
 * @returns {number}
 */
function getSqSegDist(p, p1, p2) {
  var x = p1[0];
  var y = p1[1];
  var dx = p2[0] - x;
  var dy = p2[1] - y;
  var t;
  if (dx !== 0 || dy !== 0) {
    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;
}

/**
 * basic distance-based simplification
 *
 * @param points
 * @param sqTolerance
 * @returns {*[]}
 */
function simplifyRadialDist(points, sqTolerance) {
  var prevPoint = points[0];
  var newPoints = [prevPoint];
  var i = 1;
  var n = points.length;
  var point;
  for (i; i < n; i++) {
    point = points[i];
    if (getSqDist(point, prevPoint) > sqTolerance) {
      newPoints.push(point);
      prevPoint = point;
    }
  }
  if (prevPoint !== point) {
    newPoints.push(point);
  }
  return newPoints;
}

/**
 *
 * @param points
 * @param first
 * @param last
 * @param sqTolerance
 * @param simplified
 */
function simplifyDPStep(points, first, last, sqTolerance, simplified) {
  var maxSqDist = sqTolerance;
  var i = first + 1;
  var sqDist;
  var index;
  for (i; i < last; i++) {
    sqDist = getSqSegDist(points[i], points[first], points[last]);
    if (sqDist > maxSqDist) {
      index = i;
      maxSqDist = sqDist;
    }
  }
  if (maxSqDist > sqTolerance) {
    if (index - first > 0) simplifyDPStep(points, first, index, sqTolerance, simplified);
    simplified.push(points[index]);
    if (last - index > 0) simplifyDPStep(points, index, last, sqTolerance, simplified);
  }
}

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

/**
 * both algorithms combined for awesome performance
 *
 * @param points
 * @param tolerance
 * @param highestQuality
 * @returns {number[]}
 */
export function simplify(points, tolerance, highestQuality) {
  if (points.length <= 4) return points;
  var sqTolerance = tolerance !== undefined ? tolerance * tolerance : 1;
  var newPoints = highestQuality ? points : simplifyRadialDist(points, sqTolerance);
  newPoints = simplifyDouglasPeucker(newPoints, sqTolerance);
  return newPoints;
}