githubmirror/Leaflet

src/geometry/PolyUtil.js
55 строк2 KB
Vladimir Agafonkin
ES6 modules & Rollup (#4989)
30 янв 2017, 13:35
30 янв 2017, 13:35703ae02
import * as LineUtil from './LineUtil';

/*
 * @namespace PolyUtil
 * Various utility functions for polygon geometries.
 */

/* @function clipPolygon(points: Point[], bounds: Bounds, round?: Boolean): Point[]
 * Clips the polygon geometry defined by the given `points` by the given bounds (using the [Sutherland-Hodgeman algorithm](https://en.wikipedia.org/wiki/Sutherland%E2%80%93Hodgman_algorithm)).
 * Used by Leaflet to only show polygon points that are on the screen or near, increasing
 * performance. Note that polygon points needs different algorithm for clipping
 * than polyline, so there's a seperate method for it.
 */
export function clipPolygon(points, bounds, round) {
	var clippedPoints,
	    edges = [1, 4, 2, 8],
	    i, j, k,
	    a, b,
	    len, edge, p;

	for (i = 0, len = points.length; i < len; i++) {
		points[i]._code = LineUtil._getBitCode(points[i], bounds);
	}

	// for each edge (left, bottom, right, top)
	for (k = 0; k < 4; k++) {
		edge = edges[k];
		clippedPoints = [];

		for (i = 0, len = points.length, j = len - 1; i < len; j = i++) {
			a = points[i];
			b = points[j];

			// if a is inside the clip window
			if (!(a._code & edge)) {
				// if b is outside the clip window (a->b goes out of screen)
				if (b._code & edge) {
					p = LineUtil._getEdgeIntersection(b, a, edge, bounds, round);
					p._code = LineUtil._getBitCode(p, bounds);
					clippedPoints.push(p);
				}
				clippedPoints.push(a);

			// else if b is inside the clip window (a->b enters the screen)
			} else if (!(b._code & edge)) {
				p = LineUtil._getEdgeIntersection(b, a, edge, bounds, round);
				p._code = LineUtil._getBitCode(p, bounds);
				clippedPoints.push(p);
			}
		}
		points = clippedPoints;
	}

	return points;
}