three
Version:
JavaScript 3D library
115 lines (73 loc) • 2.31 kB
JavaScript
import { Earcut } from './Earcut.js';
/**
* A class containing utility functions for shapes.
*
* @hideconstructor
*/
class ShapeUtils {
/**
* Calculate area of a ( 2D ) contour polygon.
*
* @param {Array<Vector2>} contour - An array of 2D points.
* @return {number} The area.
*/
static area( contour ) {
const n = contour.length;
let a = 0.0;
for ( let p = n - 1, q = 0; q < n; p = q ++ ) {
a += contour[ p ].x * contour[ q ].y - contour[ q ].x * contour[ p ].y;
}
return a * 0.5;
}
/**
* Returns `true` if the given contour uses a clockwise winding order.
*
* @param {Array<Vector2>} pts - An array of 2D points defining a polygon.
* @return {boolean} Whether the given contour uses a clockwise winding order or not.
*/
static isClockWise( pts ) {
return ShapeUtils.area( pts ) < 0;
}
/**
* Triangulates the given shape definition.
*
* @param {Array<Vector2>} contour - An array of 2D points defining the contour.
* @param {Array<Array<Vector2>>} holes - An array that holds arrays of 2D points defining the holes.
* @return {Array<Array<number>>} An array that holds for each face definition an array with three indices.
*/
static triangulateShape( contour, holes ) {
const vertices = []; // flat array of vertices like [ x0,y0, x1,y1, x2,y2, ... ]
const holeIndices = []; // array of hole indices
const faces = []; // final array of vertex indices like [ [ a,b,d ], [ b,c,d ] ]
removeDupEndPts( contour );
addContour( vertices, contour );
//
let holeIndex = contour.length;
holes.forEach( removeDupEndPts );
for ( let i = 0; i < holes.length; i ++ ) {
holeIndices.push( holeIndex );
holeIndex += holes[ i ].length;
addContour( vertices, holes[ i ] );
}
//
const triangles = Earcut.triangulate( vertices, holeIndices );
//
for ( let i = 0; i < triangles.length; i += 3 ) {
faces.push( triangles.slice( i, i + 3 ) );
}
return faces;
}
}
function removeDupEndPts( points ) {
const l = points.length;
if ( l > 2 && points[ l - 1 ].equals( points[ 0 ] ) ) {
points.pop();
}
}
function addContour( vertices, contour ) {
for ( let i = 0; i < contour.length; i ++ ) {
vertices.push( contour[ i ].x );
vertices.push( contour[ i ].y );
}
}
export { ShapeUtils };