Canvas vs. SVG

When I began my start-up, I knew the product was going to focus heavily on drawing high-quality graphs, so I spent quite a while looking at the various options.

 

Server Side Rendering

The first option, and the one that’s been around the longest, is to do all the rendering on the server and then send the resulting images back to the client.  This is essentially what the Google Maps did (though they’ve added more and more client-rendered elements over the years).  To do this, you’ll need some kind of image rendering environment on the server (e.g., Java2D), and, of course, a server capable of serving up the images thus produced.

I decided to skip this option because it adds latency and dramatically cuts down on interactivity and the ability to animation transitions.  Both were very important to me, so this solution was clearly not a good fit.

 

Canvas

The second option was to use HTML5’s Canvas element.  This allows you to specify a region of your webpage as a freely drawn canvas which allows all the typical 2D drawing operations.  The result is a raster image which is drawn completely using JavaScript operations.

While Canvas has the advantages of giving a lot more control on the client-side, you’re still stuck with a raster image which needs to be drawn from scratch for each change.  You also lose the structure of the scene (since it’s all reduced to pixels), and therefore lose the functionality provided in the DOM (e.g., CSS and event handlers).

 

SVG

The final option I considered (and therefore the one I chose) was using Scalable Vector Graphics (SVG).  SVG is a mark-up language, much like HTML, which is specifically designed to represent vector graphics.  You pretty much all the same primitives as with Canvas, except these are all represented as elements in the DOM, and remain accessible via JavaScript even after everything is rendered.  In particular, both CSS and JavaScript can be applied to the elements of an SVG document, making it much more suitable for the kind of interactive graphics I had in mind.

As an added incentive for using SVG, there is an excellent library called Data Driven Documents (D3) which provides an amazing resource for manipulating SVG documents with interactivity, animations, and a lot more.  More than anything else, the existence of D3 decided me on using SVG for my custom graphic needs.

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