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HTML5 Canvas, 2nd Edition
book

HTML5 Canvas, 2nd Edition

by Steve Fulton, Jeff Fulton
April 2013
Beginner
750 pages
20h 21m
English
O'Reilly Media, Inc.
Content preview from HTML5 Canvas, 2nd Edition

Resetting the Canvas clearRect Function

The clearRect() function takes in the start x,y location and the width and height to clear the Canvas:

var w=theCanvas.width;
var h=theCanvas.height;
context.clearRect(0,0,w,h);

Let’s test out using the clearRect() function by animating a path across the Canvas (Example 2-28). We will accomplish this by implementing the setTimeOut() function presented in Chapter 1. It will be used to repeatedly call our drawScreen() function and update the location of the path. The entire set of code for this example is presented because it is more involved than simply drawing a path or a shape on the Canvas at a single time.

Example 2-28. Using the clearRect() function

<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Chapter 2 Example 28: Animating a Path</title>
<script src="modernizr.js"></script>
<script type="text/javascript">
window.addEventListener('load', eventWindowLoaded, false);
function eventWindowLoaded() {

    canvasApp();

}

function canvasSupport () {
    return Modernizr.canvas;
}


function canvasApp(){


    if (!canvasSupport()) {
             return;
    }else{
        var theCanvas = document.getElementById('canvas');
        var context = theCanvas.getContext('2d');
    }

    var yOffset=0;

    function drawScreen(){

        context.clearRect(0,0,theCanvas.width,theCanvas.height);

       var currentPath=context.beginPath();
       context.strokeStyle = "red"; //need list of available colors
       context.lineWidth=5;
       context.moveTo(0, 0+yOffset);
       context.lineTo(50, 0+yOffset);
       context.lineTo(50,50+yOffset ...
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Publisher Resources

ISBN: 9781449335847Errata Page