README

points-on-curve

This package calculate the points on a curve with a certain tolerance. It can also simplify the shape to use fewer points. This can really be useful when estimating lines/polygons for curves in WebGL or for Hit/Collision detections.

Install

From npm

npm install --save points-on-curve

The package is distributed as an ES6 module.

API

pointsOnBezierCurves(points: Point[], tolerance?: number, distance?: number): Point[]

You pass in the points representing a bezier curve. Each point is an array of two numbers e.g. [100, 123].

The points can also be a set of continuous curves where the last poing on the Nth curve acts as the first point of the next.

import { pointsOnBezierCurves } from 'points-on-curve';

const curve = [[70,240],[145,60],[275,90],[300,230]];
const points = pointsOnBezierCurves(curve);
// plotPoints(points);

points on bezier

Same can be rendered with more tolerance (default value is 0.15):

const points = pointsOnBezierCurves(curve, 0.7);

points on bezier with 0.7 tolerance

Note that this method does not accept the number of points to render, but takes in a tolerance level which allows for better distribution of points.

The value of tolerance can be between 0 and 1. It is used to decide how many points are needed in a section of the curve. The algorithm determined the flatness of a section of the curve and compares it to the tolerance level, if less flat, the segment gets further divided into 2 segments.

Simplifying path

Based on the tolerance alone, this algorithm nicely provides enough points to represent a curve. It does not, however, efficiently get rid of unneeded points. The second optional argument in function, distance helps with that. If a distance value is provided, the method uses the Ramer–Douglas–Peucker algorithm to reduce the points.

const points = pointsOnBezierCurves(curve, 0.2, 0.15);

Following are the points generated with distance values of 0.15, 0.75, 1.5, and 3.0

points with 0.15d points with 0.75d points with 1.5d points with 3.0d

curveToBezier(pointsIn: Point[]): Point[]

Sometimes it's hard to think of shape as a set of cubic bezier curves, each curve with 2 controls points. It is simple to just think of them as a curve passing through a set of points.

This method turns those set of points to a set of points representing bezier curves.

import { curveToBezier } from 'points-on-curve/lib/curve-to-bezier.js';

const curvePoints = [
  [20, 240],
  [95, 69],
  [225, 90],
  [250, 180],
  [290, 220],
  [380, 80],
];
const bcurve = curveToBezier(curvePoints);
// .. Plot bcurve

Curve through points

Now that we have bezier points, these could be passed to pointsOnBezierCurves function to get the points on the curve