Those are blank to begin with, nothing is drawn, yet they'd still be
cached.
This may happen during an initial exposure (see 1a49d7d42b),
or when deleting regions.
To mitigate concurrent rendering, the waveform cache adds a random
range of pixels centered around the visible waveform.
Alignment is using integer half_width = width_samples / 2;
This always aligns the left-edge to the left-most cairo-pixel.
This fixes an issue with moving moiree patterns in waveforms when
zooming vertically (which invalidates the cache and uses a
different random number of pixels),
Generated by tools/f2s. Some hand-editing will be required in a few places to fix up comments related to timecode
and video in order to keep the legible
