leaflet
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JavaScript library for mobile-friendly interactive maps
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JavaScript
/*
* @namespace LineUtil
*
* Various utility functions for polyine points processing, used by Leaflet internally to make polylines lightning-fast.
*/
L.LineUtil = {
// Simplify polyline with vertex reduction and Douglas-Peucker simplification.
// Improves rendering performance dramatically by lessening the number of points to draw.
// @function simplify(points: Point[], tolerance: Number): Point[]
// Dramatically reduces the number of points in a polyline while retaining
// its shape and returns a new array of simplified points, using the
// [Douglas-Peucker algorithm](http://en.wikipedia.org/wiki/Douglas-Peucker_algorithm).
// Used for a huge performance boost when processing/displaying Leaflet polylines for
// each zoom level and also reducing visual noise. tolerance affects the amount of
// simplification (lesser value means higher quality but slower and with more points).
// Also released as a separated micro-library [Simplify.js](http://mourner.github.com/simplify-js/).
simplify: function (points, tolerance) {
if (!tolerance || !points.length) {
return points.slice();
}
var sqTolerance = tolerance * tolerance;
// stage 1: vertex reduction
points = this._reducePoints(points, sqTolerance);
// stage 2: Douglas-Peucker simplification
points = this._simplifyDP(points, sqTolerance);
return points;
},
// @function pointToSegmentDistance(p: Point, p1: Point, p2: Point): Number
// Returns the distance between point `p` and segment `p1` to `p2`.
pointToSegmentDistance: function (p, p1, p2) {
return Math.sqrt(this._sqClosestPointOnSegment(p, p1, p2, true));
},
// @function closestPointOnSegment(p: Point, p1: Point, p2: Point): Number
// Returns the closest point from a point `p` on a segment `p1` to `p2`.
closestPointOnSegment: function (p, p1, p2) {
return this._sqClosestPointOnSegment(p, p1, p2);
},
// Douglas-Peucker simplification, see http://en.wikipedia.org/wiki/Douglas-Peucker_algorithm
_simplifyDP: function (points, sqTolerance) {
var len = points.length,
ArrayConstructor = typeof Uint8Array !== undefined + '' ? Uint8Array : Array,
markers = new ArrayConstructor(len);
markers[0] = markers[len - 1] = 1;
this._simplifyDPStep(points, markers, sqTolerance, 0, len - 1);
var i,
newPoints = [];
for (i = 0; i < len; i++) {
if (markers[i]) {
newPoints.push(points[i]);
}
}
return newPoints;
},
_simplifyDPStep: function (points, markers, sqTolerance, first, last) {
var maxSqDist = 0,
index, i, sqDist;
for (i = first + 1; i <= last - 1; i++) {
sqDist = this._sqClosestPointOnSegment(points[i], points[first], points[last], true);
if (sqDist > maxSqDist) {
index = i;
maxSqDist = sqDist;
}
}
if (maxSqDist > sqTolerance) {
markers[index] = 1;
this._simplifyDPStep(points, markers, sqTolerance, first, index);
this._simplifyDPStep(points, markers, sqTolerance, index, last);
}
},
// reduce points that are too close to each other to a single point
_reducePoints: function (points, sqTolerance) {
var reducedPoints = [points[0]];
for (var i = 1, prev = 0, len = points.length; i < len; i++) {
if (this._sqDist(points[i], points[prev]) > sqTolerance) {
reducedPoints.push(points[i]);
prev = i;
}
}
if (prev < len - 1) {
reducedPoints.push(points[len - 1]);
}
return reducedPoints;
},
// @function clipSegment(a: Point, b: Point, bounds: Bounds, useLastCode?: Boolean, round?: Boolean): Point[]|Boolean
// Clips the segment a to b by rectangular bounds with the
// [Cohen-Sutherland algorithm](https://en.wikipedia.org/wiki/Cohen%E2%80%93Sutherland_algorithm)
// (modifying the segment points directly!). Used by Leaflet to only show polyline
// points that are on the screen or near, increasing performance.
clipSegment: function (a, b, bounds, useLastCode, round) {
var codeA = useLastCode ? this._lastCode : this._getBitCode(a, bounds),
codeB = this._getBitCode(b, bounds),
codeOut, p, newCode;
// save 2nd code to avoid calculating it on the next segment
this._lastCode = codeB;
while (true) {
// if a,b is inside the clip window (trivial accept)
if (!(codeA | codeB)) {
return [a, b];
}
// if a,b is outside the clip window (trivial reject)
if (codeA & codeB) {
return false;
}
// other cases
codeOut = codeA || codeB;
p = this._getEdgeIntersection(a, b, codeOut, bounds, round);
newCode = this._getBitCode(p, bounds);
if (codeOut === codeA) {
a = p;
codeA = newCode;
} else {
b = p;
codeB = newCode;
}
}
},
_getEdgeIntersection: function (a, b, code, bounds, round) {
var dx = b.x - a.x,
dy = b.y - a.y,
min = bounds.min,
max = bounds.max,
x, y;
if (code & 8) { // top
x = a.x + dx * (max.y - a.y) / dy;
y = max.y;
} else if (code & 4) { // bottom
x = a.x + dx * (min.y - a.y) / dy;
y = min.y;
} else if (code & 2) { // right
x = max.x;
y = a.y + dy * (max.x - a.x) / dx;
} else if (code & 1) { // left
x = min.x;
y = a.y + dy * (min.x - a.x) / dx;
}
return new L.Point(x, y, round);
},
_getBitCode: function (p, bounds) {
var code = 0;
if (p.x < bounds.min.x) { // left
code |= 1;
} else if (p.x > bounds.max.x) { // right
code |= 2;
}
if (p.y < bounds.min.y) { // bottom
code |= 4;
} else if (p.y > bounds.max.y) { // top
code |= 8;
}
return code;
},
// square distance (to avoid unnecessary Math.sqrt calls)
_sqDist: function (p1, p2) {
var dx = p2.x - p1.x,
dy = p2.y - p1.y;
return dx * dx + dy * dy;
},
// return closest point on segment or distance to that point
_sqClosestPointOnSegment: function (p, p1, p2, sqDist) {
var x = p1.x,
y = p1.y,
dx = p2.x - x,
dy = p2.y - y,
dot = dx * dx + dy * dy,
t;
if (dot > 0) {
t = ((p.x - x) * dx + (p.y - y) * dy) / dot;
if (t > 1) {
x = p2.x;
y = p2.y;
} else if (t > 0) {
x += dx * t;
y += dy * t;
}
}
dx = p.x - x;
dy = p.y - y;
return sqDist ? dx * dx + dy * dy : new L.Point(x, y);
}
};