Color-graded heatmap view

[drandyhaas]

I had some fun adding this heatmap display over the weekend:

It's in the "main" branch now if you want to try it out. It'll also be in the next release, v31.08-beta. Just turn up the persist setting, and you'll see it.

Basically, each time a trace is taken for a channel, it gets added to that channel's 2D histogram of x,y positions where traces have been. After 100 traces, the older traces start being subtracted each time a new trace is added, so the histogram stays recent. Traces are also subtracted after they "expire" after a timeout, set by the persist box setting. Then the 2D histogram is used to make a heatmap, smoothed by a Gaussian kernel, to draw behind the waveform.

I think it looks great, and it's surprisingly fast to draw! (I get about 20 Hz on my old Windows machine.)