Ryan’s Tech Blog

It now does line charts and better pie charts, and has had a lot of bugs removed since the last post. We did some code review on it at work, brought some of the spaghetti under control, and included the library in an intranet app.

Here’s a sample line graph:

The (somewhat verbose) code for this:

(defun line-chart-sample ()
  "draws a simple line chart"
  (let* ((seriesA (make-instance 'series
				 :label "SeriesA"
					;data expressed as a list (x y) pairs
				 :data '((-1 -2) (0 4) (1 5) (4 6) (5 -3))))
	 (seriesB (make-instance 'series
				 :label "SeriesB"
				 :data '((-1 4) (0 -2) (1 6) (5 -2) (6 5))))
	 (chart (make-instance 'line-chart
			       :width 400
			       :background '(.7 .7 .7)
			       :series (list seriesA seriesB))))
    (render-chart chart "line-chart-sample.png")))

I’ll probably make some easier syntax for creating series, similar to the one I made for pie slices, but for now the CLOS approach has been working decently. My data is coming from clsql, so the code ends up more concise than this example.

There are a few spots internally where it gets a little nasty, needing to pass many things around to many functions. I may end up changing the style to use “with-line-chart” functions with some global variables tracking the current chart, but I’m not sure how that would work in a multi-threaded environment. Hell, I’m not sure if my existing code will work in a multi-threaded environment. The load on this intranet app is very low, so I may be lucky enough to get away with it.