Class WeilerAthertonClipper

An implementation of the Weiler Atherton algorithm for clipping polygons. This currently only handles combinations that will not result in any holes. Support may be added for holes in the future.

This algorithm is faster than the Clipper library for this task because it relies on the unique properties of the circle, ellipse, or convex simple clip object. It is also more precise in that it uses the actual intersection points between the circle/ellipse and polygon, instead of relying on the polygon approximation of the circle/ellipse to find the intersection points.

For more explanation of the underlying algorithm, see: https://en.wikipedia.org/wiki/Weiler–Atherton_clipping_algorithm https://www.geeksforgeeks.org/weiler-atherton-polygon-clipping-algorithm https://h-educate.in/weiler-atherton-polygon-clipping-algorithm/

Constructors

constructor

Properties

clipObject config polygon CLIP_TYPES INTERSECTION_TYPES

Methods

combine intersect testForEnvelopment union

Constructors

constructor

  • new WeilerAthertonClipper(
        polygon: Polygon,
        clipObject: Rectangle | Circle,
        clipType: number,
        clipOpts: object,
    ): WeilerAthertonClipper

    Construct a WeilerAthertonClipper instance used to perform the calculation.

    Parameters

    • polygon: Polygon

      Polygon to clip

    • clipObject: Rectangle | Circle

      Object used to clip the polygon

    • clipType: number

      Type of clip to use

    • clipOpts: object

      Object passed to the clippingObject methods toPolygon and pointsBetween

    Returns WeilerAthertonClipper

Properties

clipObject

clipObject: Rectangle | Circle

config

config: object

Configuration settings

Param: config.clipType

One of CLIP_TYPES

Param: config.clipOpts

Object passed to the clippingObject methods toPolygon and pointsBetween

polygon

polygon: Polygon

StaticCLIP_TYPES

CLIP_TYPES: Readonly<{ INTERSECT: 0; UNION: 1 }> = ...

The supported clip types. Values are equivalent to those in ClipperLib.ClipType.

StaticINTERSECTION_TYPES

INTERSECTION_TYPES: Readonly<{ IN_OUT: 1; OUT_IN: -1; TANGENT: 0 }> = ...

The supported intersection types.

Methods

Staticcombine

  • combine(
        polygon: Polygon,
        clipObject: Rectangle | Circle,
        options?: { canMutate?: boolean; clipType: number },
    ): Polygon[]

    Clip a given clipObject using the Weiler-Atherton algorithm.

    At the moment, this will return a single PIXI.Polygon in the array unless clipType is a union and the polygon and clipObject do not overlap, in which case the [polygon, clipObject.toPolygon()] array will be returned. If this algorithm is expanded in the future to handle holes, an array of polygons may be returned.

    Parameters

    • polygon: Polygon

      Polygon to clip

    • clipObject: Rectangle | Circle

      Object to clip against the polygon

    • options: { canMutate?: boolean; clipType: number } = {}

      Options which configure how the union or intersection is computed

      • OptionalcanMutate?: boolean

        If the WeilerAtherton constructor could mutate or not the subject polygon points

        • Any additional properties in options (besides clipType and canMutate) are captured by the rest operator (...clipOpts) and passed to the WeilerAthertonClipper constructor.
      • clipType: number

        One of foundry.canvas.geometry.WeilerAthertonClipper.CLIP_TYPES

    Returns Polygon[]

    Array of polygons and clipObjects

Staticintersect

  • intersect(
        polygon: Polygon,
        clipObject: Rectangle | Circle,
        clipOpts?: object,
    ): Polygon[]

    Intersect a polygon and clipObject using the Weiler Atherton algorithm.

    Parameters

    • polygon: Polygon

      Polygon to clip

    • clipObject: Rectangle | Circle

      Object to clip against the polygon

    • clipOpts: object = {}

      Options passed to the clipping object methods toPolygon and pointsBetween

    Returns Polygon[]

StatictestForEnvelopment

  • testForEnvelopment(
        polygon: Polygon,
        clipObject: Rectangle | Circle,
        clipType: Readonly<{ INTERSECT: 0; UNION: 1 }>,
        clipOpts: object,
    ): Polygon[]

    Test if one shape envelops the other. Assumes the shapes do not intersect.

    1. Polygon is contained within the clip object. Union: clip object; Intersect: polygon
    2. Clip object is contained with polygon. Union: polygon; Intersect: clip object
    3. Polygon and clip object are outside one another. Union: both; Intersect: null

    Parameters

    • polygon: Polygon

      Polygon to clip

    • clipObject: Rectangle | Circle

      Object to clip against the polygon

    • clipType: Readonly<{ INTERSECT: 0; UNION: 1 }>

      One of CLIP_TYPES

    • clipOpts: object

      Clip options which are forwarded to toPolygon methods

    Returns Polygon[]

    Returns the polygon, the clipObject.toPolygon(), both, or neither.

Staticunion

  • union(
        polygon: Polygon,
        clipObject: Rectangle | Circle,
        clipOpts?: object,
    ): Polygon[]

    Union a polygon and clipObject using the Weiler Atherton algorithm.

    Parameters

    • polygon: Polygon

      Polygon to clip

    • clipObject: Rectangle | Circle

      Object to clip against the polygon

    • clipOpts: object = {}

      Options passed to the clipping object methods toPolygon and pointsBetween

    Returns Polygon[]

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