Book Image

Canvas Cookbook

Book Image

Canvas Cookbook

Overview of this book

With the growing popularity of HTML5 Canvas, this book offers tailored recipes to help you develop portable applications, presentations, and games. The recipes are simple yet creative and build on each other. At every step, the book inspires the reader to develop his/her own recipe. From basic to advanced, every aspect of Canvas API has been covered to guide readers to develop their own application, presentation, or game.
Table of Contents (16 chapters)
Canvas Cookbook
Credits
About the Author
About the Reviewer
www.PacktPub.com
Preface
Index

Drawing a rainbow


This is an implementation of a quadratic curve.

The output of our new recipe looks like this:

How to do it...

The recipe is quite simple, comprising seven calls to the function quadraticTo() to draw seven different curves.

Here is the recipe:

<html>
<head>
  <title>Rainbow</title>
  <script type="text/javascript">
    var can;
    var ctx;
    function init() {
      can = document.getElementById("MyCanvasArea");
      ctx = can.getContext("2d");
      y=can.height/2;
      x=can.width-20;
      mid=can.width/2;
      //rainbow - vibgyor
      drawQuadraticCurve(20,y,mid,0,x,y,"violet",7);
      drawQuadraticCurve(20,y-10,mid,-10,x,y-10,"indigo",7);
      drawQuadraticCurve(20,y-20,mid,-20,x,y-20,"blue",7);
      drawQuadraticCurve(20,y-30,mid,-30,x,y-30,"green",7);
      drawQuadraticCurve(20,y-40,mid,-40,x,y-40,"yellow",7);
      drawQuadraticCurve(20,y-50,mid,-50,x,y-50,"orange",7);
      drawQuadraticCurve(20,y-60,mid,-60,x,y-60,"red",7);    
      
    }
    function drawQuadraticCurve(xStart,yStart,xControl, yControl, xEnd, yEnd,color,width)
    {
      //refer the previous recipe for code
      //....
    }
  </script>
</head>
<body onload="init()">
  <canvas id="MyCanvasArea" width="800" height="400" style="border:2px solid black;" >
    browser doesn't support canvas
  </canvas>
</body>
</html>

How it works...

The drawQuadraticCurveTo() is the same function as used in the previous recipe. This function is called multiple times from the init() method.