[cairo] Isn't there a way to pass multiple points to Cairo? (sorry for duplicate)

[Andrej Mitrovic]

Yeah this was completely my mistake, this is not how waveforms should be drawn.

The stroking is what took most of the time, not the function calls.
The trick is apparently to use an average (or absolute) min and max of
several samples and then draw a vertical line between the min and max.
And when the waveform is zoomed in the lines can be drawn from one
point to another without them overlapping each other, which speeds up
drawing again.