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Canvas Clipping Region Using HTML 5

Posted by Deepak Dwij Articles | HTML 5 March 02, 2012
In this article we are going to understand working with Canvas Clipping Regions Using HTML 5. In this section we can draw a path and then use the clip() method of the canvas context.
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Introduction

In this article we are going to understand working with Canvas Clipping Regions Using HTML 5. In this section we can draw a path and then use the clip() method of the canvas context. The circle type of figure having different colors within itself, while displaying in a 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 Clipping Region 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 canvasregion.aspx

clip.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;
}
#myCanvas
{
   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 Clipping Region application.

The whole JavaScript looks as in the following.

<
script>
        window.onload = function () {
            var canvas = document.getElementById("myCanvas");
            var context = canvas.getContext("2d");
            var centerX = canvas.width / 2;
            var centerY = canvas.height / 2;
            var radius = 75;
            var offset = 50;
            context.save();
            context.beginPath();
            context.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
            context.clip();
            context.beginPath();
            context.arc(centerX - offset, centerY - offset, radius, 0, 2 * Math.PI, false);
            context.fillStyle = "#00D2FF"; // light blue
            context.fill();
            context.beginPath();
            context.arc(centerX + offset, centerY, radius, 0, 2 * Math.PI, false);
            context.fillStyle = "yellow";
            context.fill();
            context.beginPath();
            context.arc(centerX, centerY + offset, radius, 0, 2 * Math.PI, false);
            context.fillStyle = "red";
            context.fill();
            context.restore();
            context.beginPath();
            context.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
            context.lineWidth = 3;
            context.strokeColor = "black";
            context.stroke();
        };
</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 canvasregion.aspx page. Here we pass a #myCanvas in the canvas tag.

<body style="background-color: #D1D1D1">
    <center>
        <h1>
            Canvas Clipping Region
        </h1>
    </center>
    <hr />
    <canvas id="myCanvas" width="578" height="200">
        </canvas>
</body>

Step 5 : The complete code for the Clipping Region application is:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="canvasregion.aspx.cs" Inherits="Clipping_Region._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>
    </script>
</head>
<
body style="background-color: #D1D1D1">
    <center>
        <h1>
            Canvas Clipping Region
        </h1>
    </center>
    <hr />
    <canvas id="myCanvas" width="578" height="200">
        </canvas>
</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 circle type figure having different different colors within itself, while displaying in the browser.

cip 1.gif

Here are the some useful resources.

Working With Canvas Tag in HTML5
Use Canvas Tag in HTML 5
Clipping or Cropping Images in WPF
Regions and Clipping in GDI+
Explore generating visualisations using JavaScript in HTML5


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