gojs/extensionsJSM/BalloonLink.ts

/*
*  Copyright (C) 1998-2021 by Northwoods Software Corporation. All Rights Reserved.
*/

/*
* This is an extension and not part of the main GoJS library.
* Note that the API for this class may change with any version, even point releases.
* If you intend to use an extension in production, you should copy the code to your own source directory.
* Extensions can be found in the GoJS kit under the extensions or extensionsTS folders.
* See the Extensions intro page (https://gojs.net/latest/intro/extensions.html) for more information.
*/

import * as go from '../release/go-module.js';

/**
 * This custom {@link Link} class customizes its {@link Shape} to surround the comment node (the from node).
 * If the Shape is filled, it will obscure the comment itself unless the Link is behind the comment node.
 * Thus the default layer for BalloonLinks is "Background".
 *
 * If you want to experiment with this extension, try the <a href="../../extensionsJSM/BalloonLink.html">Balloon Links</a> sample.
 * @category Part Extension
 */
export class BalloonLink extends go.Link {
  private _base: number = 10;

  /**
   * Constructs a BalloonLink and sets the {@link Part#layerName} property to "Background".
   */
  constructor() {
    super();
    this.layerName = 'Background';
  }

  /**
   * Copies properties to a cloned BalloonLink.
   */
  protected cloneProtected(copy: this): void {
    super.cloneProtected(copy);
    copy._base = this._base;
  }

  /**
   * Gets or sets width of the base of the triangle at the center point of the {@link Link#fromNode}.
   *
   * The default value is 10.
   */
  get base(): number { return this._base; }
  set base(value: number) { this._base = value; }

  /**
   * Produce a Geometry from the Link's route that draws a "balloon" shape around the {@link Link#fromNode}
   * and has a triangular shape with the base at the fromNode and the top at the toNode.
   */
  public makeGeometry(): go.Geometry {
    const fromnode = this.fromNode;
    const tonode = this.toNode;
    if (fromnode === null || tonode === null) return super.makeGeometry();
    // assume the fromNode is the comment and the toNode is the commented-upon node
    const bb = fromnode.actualBounds;
    const nb = tonode.actualBounds;

    const p0 = bb.center;
    let pn = this.getPoint(this.pointsCount - 1);
    if (bb.intersectsRect(nb)) {
      pn = nb.center;
    }
    const pos = this.routeBounds;

    // compute the intersection points for the triangular arrow
    const ang = pn.directionPoint(p0);
    const L = new go.Point(this.base, 0).rotate(ang - 90).add(p0);
    const R = new go.Point(this.base, 0).rotate(ang + 90).add(p0);
    this.getLinkPointFromPoint(fromnode, fromnode, L, pn, true, L);
    this.getLinkPointFromPoint(fromnode, fromnode, R, pn, true, R);

    // form a triangular arrow from the comment to the commented node
    const fig = new go.PathFigure(pn.x - pos.x, pn.y - pos.y, true);  // filled; start at arrow point at commented node
    fig.add(new go.PathSegment(go.PathSegment.Line, R.x - pos.x, R.y - pos.y));  // a triangle base point on comment's edge
    let side = 0;
    if (L.y >= bb.bottom || R.y >= bb.bottom) side = 2;
    else if (L.x <= bb.x && R.x <= bb.x) side = 1;
    else if (L.x >= bb.right && R.x >= bb.right) side = 3;

    this.pathToCorner(side, bb, fig, pos, L, R);
    this.pathToCorner(side + 1, bb, fig, pos, L, R);
    this.pathToCorner(side + 2, bb, fig, pos, L, R);
    this.pathToCorner(side + 3, bb, fig, pos, L, R);
    fig.add(new go.PathSegment(go.PathSegment.Line, L.x - pos.x, L.y - pos.y).close());  // the other triangle base point on comment's edge

    // return a Geometry
    return new go.Geometry().add(fig);
  }

  /**
   * Draw a line to a corner, but not if the comment arrow encompasses that corner.
   */
  public pathToCorner(side: number, bb: go.Rect, fig: go.PathFigure, pos: go.Rect, L: go.Point, R: go.Point): void {
    switch (side % 4) {
      case 0: if (!(L.y <= bb.y && R.x <= bb.x)) fig.add(new go.PathSegment(go.PathSegment.Line, bb.x - pos.x, bb.y - pos.y)); break;
      case 1: if (!(L.x <= bb.x && R.y >= bb.bottom)) fig.add(new go.PathSegment(go.PathSegment.Line, bb.x - pos.x, bb.bottom - pos.y)); break;
      case 2: if (!(L.y >= bb.bottom && R.x >= bb.right)) fig.add(new go.PathSegment(go.PathSegment.Line, bb.right - pos.x, bb.bottom - pos.y)); break;
      case 3: if (!(L.x >= bb.right && R.y <= bb.y)) fig.add(new go.PathSegment(go.PathSegment.Line, bb.right - pos.x, bb.y - pos.y)); break;
    }
  }
}