Canvas Clipping Region Using HTML 5

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.

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

This is where we will create an 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 a new Webform
Rename it to canvasregion.aspx

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 is 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 on your PC. You will see the circle type figure having different colors within itself while displaying in the browser.

Here are some useful resources.

Canvas Clipping Region Using HTML 5

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Introduction