plotboilerplate/src/ts/utils/algorithms/delaunay2voronoi.ts

A simple javascript plotting boilerplate for 2d stuff.

/**
 * @author   Ikaros Kappler
 * @date     2018-04-07
 * @modified 2018-04-11 Using VoronoiCells now (was array before).
 * @modified 2020-08-15 Ported from vanilla JS to TypeScript.
 * @version  1.0.2
 **/

import { Triangle } from "../../Triangle";
import { Vertex } from "../../Vertex";
import { VoronoiCell } from "../datastructures/VoronoiCell";

/**
 * @classdesc Create the voronoi diagram from the given delaunay triangulation (they are dual graphs).
 *
 * @requires VoronoiCell
 * @requires Triangle
 */
export class delaunay2voronoi {

    public failedTriangleSets : Array<Triangle>;
    public hasErrors: boolean;

    private pointList: Array<Vertex>;
    private triangles: Array<Triangle>;
    
    constructor( pointList:Array<Vertex>, triangles:Array<Triangle> ) {

	this.failedTriangleSets = [];
	this.hasErrors          = false;

	this.pointList = pointList;
	this.triangles = triangles;
    };

    // +---------------------------------------------------------------------------------
    // | Convert the triangle set to the Voronoi diagram.
    // +-------------------------------
    build() : Array<VoronoiCell> {
	const voronoiDiagram : Array<VoronoiCell>= [];	    
	for( var p in this.pointList ) {
	    var point : Vertex = this.pointList[p];
	    // Find adjacent triangles for first point
	    var adjacentSubset : Array<Triangle> = []; 
	    for( var t in this.triangles ) {
		if( this.triangles[t].a.equals(point) || this.triangles[t].b.equals(point) || this.triangles[t].c.equals(point) ) 
		    adjacentSubset.push( this.triangles[t] );
		
	    }
	    var path : Array<Triangle> = this.subsetToPath(adjacentSubset);
	    if( path ) // There may be errors
		voronoiDiagram.push( new VoronoiCell(path,point) ); 
	}
	return voronoiDiagram;
    };


    // +---------------------------------------------------------------------------------
    // | Re-order a tiangle subset so the triangle define a single path.
    // |
    // | It is required that all passed triangles are connected to a
    // | path. Otherwise this function will RAISE AN EXCEPTION.
    // |
    // | The function has a failsafe recursive call for the case the first
    // | element in the array is inside the path (no border element).
    // +-------------------------------
    private subsetToPath( triangleSet: Array<Triangle>,
			  startPosition?:number,
			  tryOnce?:boolean ) : Array<Triangle> {
	if( triangleSet.length == 0 )
	    return [];

	if( typeof startPosition === 'undefined' )
	    startPosition = 0;
	
	let t : number = startPosition;
	const result : Array<Triangle> = [ triangleSet[t] ];
	const visited : Array<number> = [ t ];
	let i : number = 0;
	while( result.length < triangleSet.length && i < triangleSet.length ) {
	    let u : number = (startPosition+i)%triangleSet.length;
	    if( t != u && visited.indexOf(u) == -1 && triangleSet[t].isAdjacent(triangleSet[u]) ) {
		result.push(triangleSet[u]);
		visited.push(u);
		t = u;
		i = 0;
	    } else {
		i++;
	    }
	}
	// If not all triangles were used the passed set is NOT CIRCULAR.
	// But in this case the triangle at position t is at one end of the path :)
	// -> Restart with t.
	if( result.length < triangleSet.length ) {
	    if( tryOnce ) {
		// Possibility A (try to fix this): split the triangle set into two arrays and restart with each.
		// Possibility B (no fix for this): throw an error and terminate.
		// Possibility C (temp solution): Store the error for later reporting and continue.
		// this.failedTriangleSets.push( triangleSet );
		this.failedTriangleSets = triangleSet;
		this.hasErrors = true;
		// throw "Error: this triangle set is not connected: " + JSON.stringify(triangleSet);
		return null;
	    } else {
		// Triangle inside path found. Rearrange.
		return this.subsetToPath( triangleSet, t, true );
	    }
	} else {	    
	    return result;
	}
    };

}; // END delaunay2voronoi