add push method and cursor prop to polyline

lib/components/polyline.js

@@ -9,19 +9,23 @@ import { Tag } from './tag.js'
  */
 
 export class Polyline extends Tag {
+  /** @type {Vector2} */
+  cursor = new Vector2(0, 0) 
   /** @type {Vector2[]} */
   points = []
   /**
    * Initialize to "empty" rectangle
    * @type {Rectangle}
    */
   #boundingBox = new Rectangle({ x: 0, y: 0, width: 0, height: 0 })
+
   /**
    * @param {PolylineAttributes} attributes
    */
   constructor({ points = [], ...attributes } = { points: [] }) {
     super('polyline', attributes)
     this.points = points
+    this.cursor = points[points.length - 1] ?? new Vector2(0, 0)
   }
 
   /** @returns {Rectangle} */
@@ -43,6 +47,15 @@ export class Polyline extends Tag {
     return this.#boundingBox
   }
 
+  /**
+   * Adds a point to the points of the polyline.
+   * @param {Vector2} point 
+   */
+  push(point) {
+    this.points.push(point)
+    this.cursor = point
+  }
+
   render() {
     if (!Array.isArray(this.points) || this.points.length === 0) {
       throw new Error('Cannot render a Polyline without points')