Canvas Start And Stop an Animation Using HTML 5

Deepak Dwij
12y
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Introduction

In this article we are going to understand starting and stopping an animation using HTML 5 Canvas. In this section, to start an HTML5 Canvas animation, we can call a function that repeatedly requests a new animation frame, and to stop an HTML5 Canvas animation we can simply not request a new animation frame.

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 CanvasStartStopAnimation 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

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 canvasstarstopanimation.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: #F4D19F;
   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 JavaScript works, download the attached .rar file and run the CanvasStartStopAnimation application.

The whole JavaScript looks as in the following:

<script>
        window.requestAnimFrame = (function (callback)
        {
            return window.requestAnimationFrame ||
                window.webkitRequestAnimationFrame ||
                window.mozRequestAnimationFrame ||
                window.oRequestAnimationFrame ||
                window.msRequestAnimationFrame ||
               function (callback)
                {
                    window.setTimeout(callback, 1000 / 60);
                };
        })();
         function drawRect(myRectangle)
         {
            var canvas = document.getElementById("myCanvas");
            var context = canvas.getContext("2d");
            context.beginPath();
            context.rect(myRectangle.x, myRectangle.y, myRectangle.width, myRectangle.height);
            context.fillStyle = "#8ED6FF";
            context.fill();
            context.lineWidth = myRectangle.borderWidth;
            context.strokeStyle = "black";
            context.stroke();
        }
        function animate(lastTime, myRectangle, animProp)
         {
            if (animProp.animate) {
                var canvas = document.getElementById("myCanvas");
                var context = canvas.getContext("2d");
                // update
                var date = new Date();
                var time = date.getTime();
                var timeDiff = time - lastTime;
                var linearSpeed = 100;
                // pixels / second
                var linearDistEachFrame = linearSpeed * timeDiff / 1000;
                var currentX = myRectangle.x;
                if (currentX < canvas.width - myRectangle.width - myRectangle.borderWidth / 2)
                {
                    var newX = currentX + linearDistEachFrame;
                    myRectangle.x = newX;
                }
                lastTime = time;
                // clear
                context.clearRect(0, 0, canvas.width, canvas.height);
                // draw
                drawRect(myRectangle);
                // request new frame
                requestAnimFrame(function ()
                {
                    animate(lastTime, myRectangle, animProp);
                });
            }
        }
        window.onload = function ()
        {
            var myRectangle = {
                x: 0,
                y: 50,
                width: 100,
                height: 50,
                borderWidth: 5
            };
               var animProp = {
                animate: false
            };
            // add click listener to canvas
            document.getElementById("myCanvas").addEventListener("click", function ()
            {
                if (animProp.animate)
                {
                    animProp.animate = false;
                }
                else
                 {
                    animProp.animate = true;
                    var date = new Date();
                    var time = date.getTime();
                    animate(time, myRectangle, animProp);
                }
            });
            drawRect(myRectangle);
        };
</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 canvasstarstopanimation.aspx page. Here we pass a Canvas in the canvas tag.

<body style="background-color: #C9E0E6">
    <center>
        <h1>
            Canvas Start And Stop Animation
        </h1>
    </center>
    <hr />
    <canvas id="myCanvas" width="578" height="200">
        </canvas>
</body>

Step 5 : The complete code for the CanvasStartStopAnimation application:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="canvasstarstopanimation.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>
    </script>
</head>
<body style="background-color: #C9E0E6">
    <center>
        <h1>
            Canvas Start And Stop Animation
        </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. Click on the canvas to start and stop the animation, when the application runs on the browser.

Here are the some useful resources

Canvas Scaling Animation Using HTML 5
Canvas Oscillation Animation Using HTML 5
Canvas Sphere Animation Using HTML 5
Canvas Shape Tango Animation Using HTML 5
Canvas Rotating Rectangles Animation Using HTML 5

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