The value was already the nearest stored sample's, but every mark drawn for it was
placed at the *marker's* x with that sample's y -- so the dot the eye follows and the
number in the pane were a different datum whenever the marker fell between two samples.
Half a sample period is nothing across a whole window and the width of the panel once a
few samples span the axes, which is the only zoom at which anyone is asking which point
a number came from.
`place_crossings()` now goes through the plotter's new `Plot::crosshair_point()`, which
returns the quoted sample's x alongside its y -- one lookup for the mark and the number,
so they cannot name different samples. The dot consequently sits a little off its own
vertical cursor line: the line is where the marker is, the dot is the datum being quoted,
and between two samples those are two places.
Pin moves to the upstream commit that does the same for the library's own hover crosshair
and draws its mark larger than a trace's sample dots, and that keeps the old blend
reachable as `CrosshairValue::Interpolated` -- which udpscope never states.
Verified: plotter suite 370 cases 0 failed; `[cursors-probe]` lines=3 marks=6 with
`first mark at x=3.292400 y=-0.525175` against the pane's `-525.17 mV`; `[help]`
pages=14 parsed=14 closed ok.
The crosshair and the cursors pane's mix values are one library call, and it
interpolated linearly between the two samples bracketing the pointer. That is
wrong twice over here. Ingest decimation is a boxcar average over `time_stride`
samples, so a number computed between two stored samples is a second, undeclared
estimate laid over the first that nothing on screen or in an export holds. And
past the sample spacing the polyline is a line the renderer drew, so quoting a
point on it reports the drawing rather than the data.
The fix is upstream and unconditional (plotter c028f48): `crosshair_span()`'s `t`
selects the nearer end instead of blending, with a tie reading the earlier
sample. `CrosshairRow::marker` is placed from the same y, so the dot follows the
quoted sample.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
The flicker ("no data" at no constant frequency, worse with the measurements
and cursors panes up) was a torn read of the window's first stamp: acquire()
pins the window to the ring's oldest slot, and reading it at paint time races
the producer lapping it, returning a stamp one ring span too new. x0() is the
origin every trace point is reconstructed from, so one torn read produced a
refused neighbours(), a filter that dropped three quarters of the points, and
a polyline shifted off its axis. It is cached by acquire() under the lock now.
EventSeries::neighbours() answered from the (x - x0)/dx grid, whose drift from
the real arrival stamps arrives as a constant offset in seconds -- a doubling
share of the screen per zoom step, which is the "zooming into a held event
clips it more from the left" report. Both series binary-search the stamps now.
The measurements pane went through the LOD pyramid rather than reading its
window raw (19.7 ms per recompute to 1.2 ms, 0.1% of a 2 M-sample window) and
recomputes on a cadence; the math engine lost a per-slot heap allocation, a
per-sample source lookup by name and a fetch_add that cost more than the
arithmetic it counted.
The cursors pane's mix mode drew a line per *named* slot, so a slot holding a
signal that can never produce a channel -- the stream's timestamp -- got a row
that could only read "--", and such names were re-saved every session. It
counts bound traces now and apply_layout() refuses them.
Four toolbar icons are drawn for this app and compiled in as a GResource: the
stock ones were a record dot for the trigger and three magnifiers for cursors,
measurements and math.
New probes and dump lines for all of it (trace ink, measure cost, math cost,
event zoom, toolbar icons); README and CLAUDE.md record what they cure.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Martino Ferrari