phaser/src/geom/triangle/GetPoint.js

A fast, free and fun HTML5 Game Framework for Desktop and Mobile web browsers from the team at Phaser Studio Inc.

/**
 * @author       Richard Davey <rich@phaser.io>
 * @copyright    2013-2026 Phaser Studio Inc.
 * @license      {@link https://opensource.org/licenses/MIT|MIT License}
 */

var Vector2 = require('../../math/Vector2');
var Length = require('../line/Length');

/**
 * Returns a point along the perimeter of a Triangle as a Vector2, based on a normalized position value.
 *
 * The `position` parameter is a value between 0 and 1, where 0 and 1 both map to the start of
 * line A (the first vertex). The point is calculated by traversing the triangle's perimeter in
 * order: line A, then line B, then line C.
 *
 * @function Phaser.Geom.Triangle.GetPoint
 * @since 3.0.0
 *
 * @generic {Phaser.Math.Vector2} O - [out,$return]
 *
 * @param {Phaser.Geom.Triangle} triangle - The Triangle to get the point on its perimeter from.
 * @param {number} position - A normalized value between 0 and 1 representing a position along the triangle's perimeter. Both 0 and 1 return the start of line A.
 * @param {Phaser.Math.Vector2} [out] - An optional Vector2 point to store the result in. If not given, a new Vector2 will be created.
 *
 * @return {Phaser.Math.Vector2} A Vector2 point containing the coordinates of the position on the triangle's perimeter.
 */
var GetPoint = function (triangle, position, out)
{
    if (out === undefined) { out = new Vector2(); }

    var line1 = triangle.getLineA();
    var line2 = triangle.getLineB();
    var line3 = triangle.getLineC();

    if (position <= 0 || position >= 1)
    {
        out.x = line1.x1;
        out.y = line1.y1;

        return out;
    }

    var length1 = Length(line1);
    var length2 = Length(line2);
    var length3 = Length(line3);

    var perimeter = length1 + length2 + length3;

    var p = perimeter * position;
    var localPosition = 0;

    //  Which line is it on?

    if (p < length1)
    {
        //  Line 1
        localPosition = p / length1;

        out.x = line1.x1 + (line1.x2 - line1.x1) * localPosition;
        out.y = line1.y1 + (line1.y2 - line1.y1) * localPosition;
    }
    else if (p > length1 + length2)
    {
        //  Line 3
        p -= length1 + length2;
        localPosition = p / length3;

        out.x = line3.x1 + (line3.x2 - line3.x1) * localPosition;
        out.y = line3.y1 + (line3.y2 - line3.y1) * localPosition;
    }
    else
    {
        //  Line 2
        p -= length1;
        localPosition = p / length2;

        out.x = line2.x1 + (line2.x2 - line2.x1) * localPosition;
        out.y = line2.y1 + (line2.y2 - line2.y1) * localPosition;
    }

    return out;
};

module.exports = GetPoint;