# How to Create a luminous Loop

Source: Internet
Author: User

First, let's take a look at the running effect of the luminous link:

This demo mainly contains three technical points: one is how to make the entire loop glow when selecting a link, and the other is how to draw a curve link with an arrow; third, how to set the link style to make the overall control.
1. How to obtain all links of the entire loop and make it glow

`function createCircuit(nodes, linename, flag) {    if (flag) {        var startNode = nodes[0];        var stopNode = nodes[nodes.length - 1];        var link = new CLink(stopNode, startNode);        link.setStyle(‘link.type‘, "extend.left");//        link.setName(linename);        link.setClient(‘linename‘, linename);        box.add(link);    }    for (var i = 0; i < nodes.length - 1; i++) {        var fromNode = nodes[i];        var toNode = nodes[i + 1];        var link = new CLink(fromNode, toNode);//        link.setName(linename);        link.setClient(‘linename‘, linename);        if (i == 0) {            link.setStyle(‘link.type‘, "orthogonal.H.V");//orthogonal\        } else if (i == 1) {            link.setStyle(‘link.type‘, "orthogonal.V.H");//orthogonal\        } else if (i == 2) {            link.setStyle(‘link.type‘, "orthogonal.V.H");//orthogonal\        }//       link.setStyle(‘link.type‘, "orthogonal");//orthogonal\        box.add(link);    }}`

2. Custom Implementation of curve link with arrows
This mainly investigates the canvas rendering capability. The core code is as follows:

`cx = cx - Math.cos(angle) * radius;        cy = cy - Math.sin(angle) * radius;        ctx.lineWidth = 4;        ctx.beginPath();        ctx.moveTo(p1.x, p1.y - h1 / 2);        ctx.quadraticCurveTo(cx, cy, p2.x, p2.y - h2 / 2);        ctx.stroke();        ctx.closePath();       //draw arrow        this.drawArrow(ctx, p2.x, p2.y - h2 / 5 * 3, cx, cy+20, 1, 2, Math.PI / 8, 10);`

3. Set the link Style
Twaver links support many styles. For common types, refer to this document. This article mainly monitors the mousemove event and constantly calculates the relative positions between nodes during node dragging to determine the link type, and constantly refresh.

The core code is as follows:

`function refreshLinkType() {    box.forEach(function (element) {        if (element instanceof  twaver.Link) {            var fromNode = element.getFromNode();            var toNode = element.getToNode();            var nextLinks = toNode.getLinks();            var nextNode;            nextLinks.forEach(function (element) {                if (element.getToNode() !== toNode) {                    nextNode = element.getToNode();                }            });            var fromPoint = fromNode.getCenterLocation();            var toPoint = toNode.getCenterLocation();            var nextPoint;            if (nextNode) {                nextPoint = nextNode.getCenterLocation();            }            //compute the relationship of location between fromNode and toNode            if (fromPoint.x < toPoint.x && fromPoint.y < toPoint.y) {                element.setStyle(‘link.type‘, "orthogonal.V.H");            } else if (fromPoint.x < toPoint.x && fromPoint.y > toPoint.y) {                element.setStyle(‘link.type‘, "orthogonal.V.H");            } else if (fromPoint.x > toPoint.x && fromPoint.y < toPoint.y) {                element.setStyle(‘link.type‘, "orthogonal.V.H");            } else if (fromPoint.x > toPoint.x && fromPoint.y > toPoint.y) {                element.setStyle(‘link.type‘, "orthogonal");            }            if (nextPoint) {                if (toPoint.x > fromPoint.x && toPoint.x > nextPoint.x) {                    if (toPoint.y > fromPoint.y && toPoint.y < nextPoint.y) {                        element.setStyle(‘link.type‘, "orthogonal.H.V");                    } else {                        element.setStyle(‘link.type‘, "orthogonal.V.H");                    }                }            }        }    });}`

How to Create a luminous Loop

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