Book Image

HTML5 Canvas Cookbook

By : Eric Rowell
Book Image

HTML5 Canvas Cookbook

By: Eric Rowell

Overview of this book

The HTML5 canvas is revolutionizing graphics and visualizations on the Web. Powered by JavaScript, the HTML5 Canvas API enables web developers to create visualizations and animations right in the browser without Flash. Although the HTML5 Canvas is quickly becoming the standard for online graphics and interactivity, many developers fail to exercise all of the features that this powerful technology has to offer.The HTML5 Canvas Cookbook begins by covering the basics of the HTML5 Canvas API and then progresses by providing advanced techniques for handling features not directly supported by the API such as animation and canvas interactivity. It winds up by providing detailed templates for a few of the most common HTML5 canvas applications—data visualization, game development, and 3D modeling. It will acquaint you with interesting topics such as fractals, animation, physics, color models, and matrix mathematics. By the end of this book, you will have a solid understanding of the HTML5 Canvas API and a toolbox of techniques for creating any type of HTML5 Canvas application, limited only by the extent of your imagination.
Table of Contents (19 chapters)
HTML5 Canvas Cookbook
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Canvas Security
Index

Rotating the canvas context


The next type of transformation available with the HTML5 canvas API, and quite arguably the handiest, is the rotation transform. In this recipe, we'll first position the canvas context with a translation transform, and then we'll rotate the context with rotate() method.

How to do it...

Follow these steps to draw a rotated rectangle:

  1. Define the canvas context and the dimensions for the rectangle:

    window.onload = function(){
        var canvas = document.getElementById("myCanvas");
        var context = canvas.getContext("2d");
        
        var rectWidth = 150;
        var rectHeight = 75;
  2. Translate the canvas context and then rotate it by 45 degrees:

        // translate context to center of canvas
        context.translate(canvas.width / 2, canvas.height / 2);
      
        // rotate context 45 degrees clockwise
        context.rotate(Math.PI / 4);
  3. Draw the rectangle:

        context.fillStyle = "blue";
        context.fillRect(-rectWidth / 2, -rectHeight / 2, rectWidth, rectHeight);
    };
  4. Embed the canvas tag inside...