D3.js Delaunay.trianglePolygons() Method

Last Updated : 07 Mar, 2024

D3.js is a strong JavaScript framework for data visualization, and one of its modules, Delaunay, supports Delaunay triangulation. The Delaunay.trianglePolygons() Method returns an iterable over the polygons for each triangle, in order.

Syntax:

Delaunay.trianglePolygons()

Parameters:

This method takes no parameters.

Return Value:

This method returns an Iterable over the polygons.

Example 1: The below code example shows the use of the Delaunay.trianglePolygons() method.

HTML

<!DOCTYPE html>
<html>
 
<head>
    <meta charset="utf-8">
    <script src=
"https://d3js.org/d3.v5.min.js">
    </script>
</head>
 
<body>
    <h1 style="text-align: center; 
        color: green;">
        GeeksforGeeks
    </h1>
    <h3 style="text-align: center;">
        D3.js | d3.trianglePolygons() Method
    </h3>
 
    <div id="app" style="text-align: center; 
            margin-top: 20px; 
            font-size: 18px;">
    </div>
 
    <script type="module">
        import * as d3 from "https://cdn.skypack.dev/d3@7";
 
        const canvasWidth = 400;
        const canvasHeight = 300;
        const canvas =
            document.createElement("canvas");
        const context =
            canvas.getContext("2d");
 
        canvas.width = canvasWidth;
        canvas.height = canvasHeight;
 
        const data = Array(50)
            .fill()
            .map((_, i) => ({
                x: (i * canvasWidth) / 50,
                y: Math.random() * canvasHeight
            }));
 
        const voronoi = d3.Delaunay.from(
            data,
            (d) => d.x,
            (d) => d.y
        ).voronoi([0, 0, canvasWidth, canvasHeight]);
 
        context.clearRect(0, 0, canvasWidth, canvasHeight);
 
        context.fillStyle = "black";
        context.beginPath();
        voronoi.delaunay.renderPoints(context, 1);
        context.fill();
 
        context.lineWidth = 1.5;
        const segments =
            voronoi.render().split(/M/).slice(1);
        for (const e of segments) {
            context.beginPath();
            context.strokeStyle =
                d3.hsl(360 * Math.random(), 0.7, 0.5);
            context.stroke(new Path2D("M" + e));
        }
 
        const trianglePolygons =
            voronoi.delaunay.trianglePolygons();
        console.log(trianglePolygons)
 
        document.querySelector("#app").
            appendChild(canvas);
    </script>
</body>
 
</html>

Output:

resize-1709472822368222932Screenshot202403031859001-(1)

Example 2: The below code uses the d3.Delaunay.trianglePolygons() method to render the individual triangles of a Delaunay triangulation on a canvas.

HTML

<!DOCTYPE html>
<html>
 
<head>
    <meta charset="utf-8">
    <script src="https://d3js.org/d3.v7.min.js"></script>
</head>
 
<body style="text-align: center;">
    <h1 style="text-align: center; color: green;">
        GeeksforGeeks
    </h1>
    <h3 style="text-align: center;">
        D3.js | Delaunay Triangles with trianglePolygons()
    </h3>
 
    <div id="app" style=
        "text-align: center; 
        margin-top: 20px;">
    </div>
 
    <script type="module">
        import * as d3 from "https://cdn.skypack.dev/d3@7";
 
        const width = 600;
        const height = 400;
 
        const points = Array.from({ length: 50 }, 
            () => [Math.random() * width, 
                Math.random() * height]);
 
        const delaunay = d3.Delaunay.from(points);
 
        const triangles = delaunay.trianglePolygons();
 
        const canvas = d3.select("#app")
            .append("canvas")
            .attr("width", width)
            .attr("height", height);
 
        const context = 
            canvas.node().getContext("2d");
 
        context.beginPath();
        delaunay.renderPoints(context);
        context.fillStyle = "black";
        context.fill();
 
        context.lineWidth = 2;
        for (const triangle of triangles) {
            context.beginPath();
            context.strokeStyle = "blue";
            context.moveTo(triangle[0][0], triangle[0][1]);
            for (const point of triangle) {
                context.lineTo(point[0], point[1]);
            }
            context.closePath();
            context.stroke();
        }
    </script>
</body>
 
</html>