I Have A Canvas And A JavaScript Paintbrush

One of the biggest problems of the Internet today is an over-reliance on proprietary plugins. Mac users will be especially familiar with the feelings of abject rage as a Flash game bogs down their system, takes over a chunk of memory, and causes the fans in their laptop to whir consistently, due to the lack of hardware acceleration in the Mac version of Flash Player (which was only recently remedied). There's Flash, Silverlight, Java, and whatever proprietary single-use plugin TV networks' websites make you install to watch their shows.

"So what?" you say. "I just install the plugins when I need them. No big deal." Yeah...except each one requires a download, an installation, and a browser restart. It's a hassle. (And we won't get into cross-platform issues.)

Better than that, each plugin introduces its own set of security holes. Flash is notorious for this, but it is not alone in that regard.

Plugins used to be the only way to provide interactivity to a website. Something better is looming on the horizon, though: HTML5, and with it, <canvas>, <video>, and <audio>.

The video and audio tags are fairly self-explanatory. As long as the browser properly implements them, they provide plugin-free playback for videos and sound, respectively. Canvas is an HTML tag that essentially gives you a blank area that you draw on using JavaScript. The code required is fairly similar to creating graphics in a Java applet, for those of you who are familiar with that.

Java Applet Code:
g.setColor(new Color(0x5E, 0x2F, 0x00));
g.fillRect(0, 180, 200, 50);

JavaScript Canvas Code:
ctx.fillStyle = "#5E2F00";
ctx.fillRect(0, 180, 200, 50);

Canvas/JavaScript provides no easy way, however, to draw ovals or rounded shapes. Compare the two methods for drawing a rectangle with rounded corners:

Java Applet Code:
g.setColor(Color.white);
g.fillRoundRect(45, 35, 50, 35, 10, 10);
g.setColor(Color.black);
g.drawRoundRect(45, 35, 50, 35, 10, 10);

JavaScript Canvas Code:
ctx.fillStyle = "#FFFFFF";
ctx.strokeStyle = "#000000";
ctx.beginPath();
ctx.moveTo(45, 45);
ctx.quadraticCurveTo(45, 35, 55, 35);
ctx.lineTo(85, 35);
ctx.quadraticCurveTo(95, 35, 95, 45);
ctx.lineTo(95, 60);
ctx.quadraticCurveTo(95, 70, 85, 70);
ctx.lineTo(55, 70);
ctx.quadraticCurveTo(45, 70, 45, 60);
ctx.lineTo(45, 45);
ctx.fill();
ctx.stroke();
ctx.closePath();

Even with that convoluted code, I still saved approximately 60 lines of code generating this image in JavaScript with canvas than it took to do the same thing in a Java applet. Most of this savings probably came from the fact that JavaScript has both a fillStyle and a strokeStyle, while Java uses setColor() for everything, necessitating more color changes. Plus, the user doesn't have to install a plugin to make it work, it renders pretty much instantaneously in the browser window, and you could copy the generated image and save it if you wanted to, which would be useful if you wanted to code a drawing web app of some sort.

Want to learn more about drawing with <canvas>?

• HTML 5 canvas - the basics
• Canvas tutorial - MDC
• W3Schools HTML5 tutorial (for HTML5 in general, not canvas specifically)