Canvas Transformation State Stack Using HTML 5

Deepak Dwij
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Introduction

In this article, we are going to understand the concept of canvas transformation state stack using HTML 5. We are also going to learn about various transformation states with the HTML5 Canvas and how to understand the save() and restore() methods of the canvas context.

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 CanvasStateStack 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 statestack.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;
}
Canvas
{
border: 2px solid #9C9898;
margin-top: 50px;
margin-left: 50px;
background-color: #009999;
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. To fully understand how the JavaScript works, download the attached .rar file and run the CanvasStateStack application.

The whole JavaScript looks as in the following.

<script>
window.onload = function ()
{
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var rectWidth = 150;
var rectHeight = 75;
context.save();
context.translate(canvas.width / 2, canvas.height / 2);
context.save();
context.rotate(Math.PI / 4);
context.save();
context.scale(2, 2);
context.fillStyle = "blue";
context.fillRect(-rectWidth / 2, -rectHeight / 2, rectWidth, rectHeight);
context.restore();
context.fillStyle = "red";
context.fillRect(-rectWidth / 2, -rectHeight / 2, rectWidth, rectHeight);
context.restore();
context.fillStyle = "white";
context.fillRect(-rectWidth / 2, -rectHeight / 2, rectWidth, rectHeight);
context.restore();
};
</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 statestack.aspx page. Here we pass a Canvas in the canvas tag.

<body style="background-color: #FFFFCC">
<center>
<h2>
Canvas State Stack
</h2>
</center>
<hr />
<canvas id="myCanvas" width="500" height="200">
</canvas>
</body>

Step 5 : The complete code for the CanvasStateStack application:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="statestack.aspx.cs" Inherits="CanvasStateStack.statestack" %>
<!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: #FFFFCC">
<center>
<h2>
Canvas State Stack
</h2>
</center>
<hr />
<canvas id="myCanvas" width="500" 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 canvas state stack while displaying it in the browser.