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| Title: LineElement.ts |
| A port of the software Geometry Applet by |
| Author: David E. Joyce |
| Department of Mathematics and Computer Science |
| Clark University |
| Worcester, MA 01610-1477 |
| U.S.A. |
| |
| http://aleph0.clarku.edu/~djoyce/home.html |
| djoyce@clarku.edu |
| |
| Date: February, 1996. Version 2.0.0 May, 1997. |
| TypeScript Port: 2019, Nelson Brown, brownnrl@gmail.com |
| https://www.nelsonbrown.net/ |
+----------------------------------------------------------------------*/
import {PointElement} from "../point/PointElement";
import {GeomElement} from "../GeomElement";
import {SlateCanvas} from "../../Slate";
export class PolygonElement extends GeomElement {
public V : PointElement[];
// Face fill alpha — drives drawFace's globalAlpha independent of
// drawProgress (which drives the edge trace). Lets an animation
// run the outline to completion at drawProgress = 1 first, then
// separately fade the fill in by ticking faceAlpha 0 → 1. Default
// 1 means "fully opaque" — every existing render path behaves
// identically.
private _faceAlpha : number = 1;
set faceAlpha(value: number) {
this._faceAlpha = value < 0 ? 0 : (value > 1 ? 1 : value);
}
get faceAlpha(): number { return this._faceAlpha; }
constructor(ps?: PointElement[]) {
super();
this.dimension = 2;
if (ps == null) {
this.V = [];
return;
}
this.V = ps;
}
public area() : number {
// Ported from PolygonElement.java area() — 2026-04-12
// Compute the area of this polygon (assuming it's planar & convex).
// Uses fan triangulation from V[0].
let sum = 0.0;
for (let i = 0; i < this.V.length - 2; ++i) {
sum += PointElement.area(this.V[0], this.V[i + 1], this.V[i + 2]);
}
return sum;
}
public drawEdge(c: HTMLCanvasElement, color?: string): void {
if (!this.visible && !this.shouldHighlight && this.emphasisAmount <= 0) return;
if (color == null) {
if (this.emphasized || this.shouldHighlight) {
color = this.edgeHighlightColor;
} else {
color = this.edgeColor;
}
}
if (color == null) return;
if (this.V.length <= 1) return;
let ctx = c.getContext("2d");
ctx.beginPath();
ctx.strokeStyle = color;
{
const baseW = this.shouldHighlight ? 3 : 1;
ctx.lineWidth = (baseW + this.emphasisAmount * (6 - baseW)) * GeomElement.styleScale;
}
// Edge enumeration: a closed polygon (>2 verts) has V.length
// edges including the closing one; an open polyline has
// V.length - 1. Each integer step of drawProgress · edgeCount
// advances one full edge; the fractional remainder partially
// traces the next. drawProgress = 1 (default) reproduces the
// pre-animation full-trace behaviour bit-for-bit.
let n = this.V.length;
let isClosed = n > 2;
let edgeCount = isClosed ? n : n - 1;
let p = this.drawProgress;
let totalProgress = p * edgeCount;
let fullEdges = Math.floor(totalProgress);
let fractionalEdge = totalProgress - fullEdges;
ctx.moveTo(this.V[0].x, this.V[0].y);
for (let i = 0; i < fullEdges; i++) {
let to = this.V[(i + 1) % n];
ctx.lineTo(to.x, to.y);
ctx.stroke();
}
if (fractionalEdge > 0 && fullEdges < edgeCount) {
let from = this.V[fullEdges];
let to = this.V[(fullEdges + 1) % n];
let px = from.x + (to.x - from.x) * fractionalEdge;
let py = from.y + (to.y - from.y) * fractionalEdge;
ctx.lineTo(px, py);
ctx.stroke();
}
}
public defined() : boolean {
if (this.V.length == 0) return false;
for(let v of this.V) {
if (!v.defined()) return false;
}
return true;
}
public drawFace(c: SlateCanvas): void {
if (!this.visible && !this.shouldHighlight && this.emphasisAmount <= 0) return;
if(this.faceColor != null && this.defined() && this.V.length > 2) {
let ctx : CanvasRenderingContext2D = c.getContext("2d") as CanvasRenderingContext2D;
ctx.beginPath();
ctx.fillStyle = this.faceColor;
let firstPoint = this.V[0];
let rest = this.V.slice(1);
ctx.moveTo(firstPoint.x, firstPoint.y);
for(let vertex of rest)
ctx.lineTo(vertex.x, vertex.y);
ctx.closePath();
// Animate the fill via the dedicated faceAlpha field so
// outline-then-fill animations can run the edge trace to
// completion at drawProgress = 1 first, then independently
// tick faceAlpha from 0 to 1 for the fade-in. Default
// faceAlpha = 1 preserves the fully-opaque behaviour for
// every consumer that doesn't animate.
let a = this.faceAlpha;
if (a < 1) {
if (a <= 0) return; // fully transparent — skip
ctx.save();
ctx.globalAlpha = a;
ctx.fill();
ctx.restore();
} else {
ctx.fill();
}
}
}
public drawName(c: SlateCanvas): void {
if (!this.visible && !this.shouldHighlight && this.emphasisAmount <= 0) return;
if (this.nameColor != null && this.name != null && this.defined()) {
let x : number = 0;
let y : number = 0;
for(let v of this.V) {
x += v.x;
y += v.y;
}
let n : number = this.V.length;
x = x / n;
y = y / n;
let ctx : CanvasRenderingContext2D = c.getContext("2d") as CanvasRenderingContext2D;
let [w, h] = this._getTextMetrics(ctx, this._name);
ctx.beginPath();
ctx.fillStyle = this.nameColor;
ctx.fillText(this._name, x - w/2., y + h/4.);
}
}
public drawVertex(c: SlateCanvas): void {
if (!this.visible && !this.shouldHighlight && this.emphasisAmount <= 0) return;
if (this.vertexColor != null && this.defined() ) {
for(let v of this.V) {
v.drawVertex(c, this.vertexColor);
}
}
}
public rotate(pivot: PointElement, ac: number, as: number): void {
}
public translate(dx: number, dy: number): void {
}
public update(): void {
}
}
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