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Comment by tzaman | Hacker News Reader

Welcome back. Nick, if you want it to be really successful, add a little bit of interactivity, at least labels to pie/doughnut charts and hover values on line charts. Then it's perfect.

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The project mentions that this was an intentional design decision. The graph's are written to a canvas element, which means a low memory footprint and the ability to save graphs as images. I believe they'd need to switch over to using SVG elements for graphs if there are plans to add DOM events to chart elements.

Canvas can be used for labels and interactivity too: http://chartbeat.com/publishing/demo/

Clicks and hovers can be done on canvas, using hack that renders on second (invisible) canvas each object with its own, constant color and then checking color of the pixel at coordinates of cursor. It would probably need some kind of scene abstraction though.

Alternatively, just put some invisible DOM elements on top of the canvas and put your click handlers on those. It's imagemaps all over again ;)

This is how flot works. The base chart is drawn on canvas. All labels including axes, legends and mouseovers are DOM elements that are absolutely positioned over the canvas.

The canvas itself is always inside a canvascontainer div that also contains all the other dom elements.

"some kind of scene abstraction":

http://simianzombie.com/files/javascript/canvasui4.html

... and then he'd just be re-implementing (highcharts)[http://highcharts.com]

A freely available charting library with the same capabilities as highcharts would be a welcome thing for many people.

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