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Canvas Anchor Points Using HTML 5

Posted by Deepak Dwij Articles | HTML 5 March 03, 2012
In this article we are going to understand the concept of Canvas Anchor Points Using HTML 5. In this section you will see the anchor points of the quadratic curve and the Bezier curve in your browser.
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Introduction

In this article we are going to understand the concept of Canvas Anchor Points Using HTML 5. In this section you will see the anchor points of the quadratic curve and the Bezier curve in your browser.

Here we will use some JavaScript and some styles along with HTML code. Just go through the steps to see how to create this application.

Let's see how the AnchorPoints application can be created. To do so use the following steps.

Step 1 : Open a HTML editor or Visual Studio.
sd.gif

Open File menu ->select new ->Choose Website then.

0000.jpg

This is where we will create the HTML5 application.

  • Go to Solution Explorer
  • Right-click on the Application name
  • Select Add-->add new item
  • Now in the window that opens, select an HTML page or new Web form
  • Rename it to AnchorPoints.aspx

anchor1.gif

Step 2 : In this section we will create the style for the media and create the .css on the media screen. Put the given script in the Head section of the HTML or between the <head>--</head> tags. Here the CSS are used for design purposes.

CSS Script

<style>
body
{
  margin: 0px;
  padding: 0px;
  font-family: Comic Sans MS;
  outline-color: Yellow;
}
Canvas
{
   border: 2px solid #9C9898;
   margin-top: 50px;
   margin-left: 60px;
   background-color: #00B2EE;
   box-shadow: 5px 5px 8px #222;
 }
.title
{
   text-align: center;
   font-family: Segoe UI Light, Arial, Helvetica;
   font-size: 2.2em;
   margin: 1em;
}
.info
{
   text-align: center;
   font-family: Segoe UI Light, Arial, Helvetica;
   font-size: 1.2em;
   margin: 0.25em;
}
</style>

Step 3 : In this part we need to work on some JavaScript. For fully understanding how the JavaScript works, download the attached .rar file and run the AnchorPoints application.

The whole JavaScript looks as in the following.

<script>
        function buildAnchor(curveLayer, anchorsLayer, x, y, anchor)
         {
           var anchor = new Kinetic.Circle({
                x: x,
                y: y,
                radius: 5,
                stroke: "#666",
              fill: "#ddd",
                strokeWidth: 2,
               draggable: true
            });
            // set curve points on dragmove
            anchor.on("dragmove", function ()
            {
                drawCurves(curveLayer);
            });
            // add hover styling
            anchor.on("mouseover", function ()
            {
                document.body.style.cursor = "pointer";
                this.setStrokeWidth(4);
                anchorsLayer.draw();
            });
            anchor.on("mouseout", function ()
            {
                document.body.style.cursor = "default";
                this.setStrokeWidth(2);
                anchorsLayer.draw();
            });
           anchorsLayer.add(anchor);
            return anchor;
        }
        function drawCurves(curveLayer)
         {
            var context = curveLayer.getContext();
            curveLayer.clear();   
            var quad = curveLayer.quad;
            // draw curve
            context.beginPath();
            context.moveTo(quad.start.x, quad.start.y);
            context.lineTo(quad.control.x, quad.control.y);
            context.lineTo(quad.end.x, quad.end.y);
            context.strokeStyle = "#ccc";
            context.lineWidth = 2;
            context.stroke();
            context.closePath();
            // draw connectors
            context.beginPath();
            context.moveTo(quad.start.x, quad.start.y);
            context.quadraticCurveTo(quad.control.x, quad.control.y, quad.end.x, quad.end.y);
            context.strokeStyle = "red";
            context.lineWidth = 4;
            context.stroke();
            var bezier = curveLayer.bezier;
            // draw curve
            context.beginPath();
            context.moveTo(bezier.start.x, bezier.start.y);
            context.lineTo(bezier.control1.x, bezier.control1.y);
            context.lineTo(bezier.control2.x, bezier.control2.y);
            context.lineTo(bezier.end.x, bezier.end.y);
            context.strokeStyle = "#ccc";
            context.lineWidth = 2;
            context.stroke();
            context.closePath();
            // draw connectors
            context.beginPath();
            context.moveTo(bezier.start.x, bezier.start.y);
            context.bezierCurveTo(bezier.control1.x, bezier.control1.y, bezier.control2.x, bezier.control2.y, bezier.end.x, bezier.end.y);
            context.strokeStyle = "blue";
            context.lineWidth = 4;
            context.stroke();
        }
        window.onload = function ()
        {
            var stage = new Kinetic.Stage("container", 578, 200);
            var curveLayer = new Kinetic.Layer();
            var anchorsLayer = new Kinetic.Layer();
            curveLayer.quad = {
                start: buildAnchor(curveLayer, anchorsLayer, 60, 30),
              control: buildAnchor(curveLayer, anchorsLayer, 240, 110),
                end: buildAnchor(curveLayer, anchorsLayer, 80, 160)
            };
            curveLayer.bezier = {
                start: buildAnchor(curveLayer, anchorsLayer, 280, 20),
                control1: buildAnchor(curveLayer, anchorsLayer, 530, 40),
                control2: buildAnchor(curveLayer, anchorsLayer, 480, 150),
                end: buildAnchor(curveLayer, anchorsLayer, 300, 150)
            };
            stage.on("mouseout", function ()
            {
                drawCurves(curveLayer);
                anchorsLayer.draw();
            });
            stage.add(curveLayer);
            stage.add(anchorsLayer);
            drawCurves(curveLayer);
        };
</script>

Step 4 : In this section we are going to become familiar with the body part of HTML scripting. Replace this script from the body section of the AnchorPoints.aspx page. Here we pass a Canvas in the canvas tag.

<body style="background-color: #00CED1">
    <center>
        <h2>
            Anchor Points
        </h2>
    </center>
    <hr />
    <div id="container">
    </div>
</body>

Step 5 : The complete code for the
AnchorPoints application.

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="AnchorPoints.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <style>
    </style>
    <script src="jscript.js">
    </script>
    <script>
    </script>
</head>
<
body style="background-color: #00CED1">
    <center>
        <h2>
            Anchor Points
        </h2>
    </center>
    <hr />
    <div id="container">
    </div>
</body>
</
html>

Step 6 : Output Press F5

Note :
For the accurate output of HTML5 applications, you must have the Google Chrome browser in your PC. You
will see the anchor points of the quadratic curve and the Bezier curve in your browser.

anchor2.gif

Here are the some useful resources.

Use of Anchor, Comment and DOCTYPE in HTML 5
Use Canvas Tag in HTML 5
Working With Spinning Points in HTML 5
Explore generating visualisations using JavaScript in HTML5
Canvas in HTML 5


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