`format_time()` picked its sub-second rung from the raw value, so three
significant figures of a value just under a rung's top rounded to 1000 and
`%.3g` wrote that as an exponent: a one-second tick computed as 0.9999999 s
read `1e+03ms`. The rung is now chosen by the rounded mantissa, which is the
same 999.5 check `format_si()` already made for the SI prefixes, and a value
that rounds to a whole second leaves the sub-second branch entirely.
A host zooming into a sub-second window cannot label it absolutely: Time
formatting uses three significant digits, so 12.345671s and 12.345672s are the
same string and a 1 ms step around a multi-second time is unlabelled. The axis
gains an `origin`: every value it writes is `v - origin`, and the ticks are
generated on the shifted grid, so the window reads 0, 500us, 1ms.
`origin_follows_range` re-takes the origin from the axis' own range on every
refresh -- the mode a *moving* window needs, since the edge is derived from the
newest sample at layout time and a value the host wrote a frame earlier is a
frame of scroll stale.
`format_time` now scales its sub-second values by prefix, the way `format_si`
does on a y axis: the unit that keeps the mantissa in [1, 1000). A fixed
millisecond unit printed 0.005ms where 5us is the reading, and 1e-05ms where
10ns is. An exact zero prints `0`, the same convention `format_si` states. The
origin subtraction's dust is snapped by a *relative* epsilon, so a tick on the
origin reads 0 rather than 1.78e-12ms.
Tested by `ticks_are_written_relative_to_an_axis_origin`,
`a_range_origin_puts_the_zero_tick_on_the_left_edge` and the extended
`format_time_shapes`; the suite is 359 cases, 0 failed.
A range straddling zero never lands *on* zero: the walk starts at
`ceil(min / stride) * stride`, which is not representable whenever the stride is
not a power of two -- 0.1 and 0.2 are the everyday ones -- so the tick that means
zero arrives a few ULP off and `format_si` labels it from six prefixes down.
`[-1, 1]` read `-1 -500m -139a 500m 1`. Deriving the tick by multiplication
rather than accumulation does not help, because the error is already in the
first term.
Every tick is an integer multiple of the stride, so the smallest magnitude a
non-zero tick can have is the stride itself, while the residue is a few ULP of
the range -- ten orders of magnitude apart. Anything inside a millionth of the
stride is therefore the origin and nothing else. It is stored as exactly `0.0`
rather than merely labelled so: `Axis::refresh()` re-formats a time axis from
`tick.value`, where the same residue reads `3.19e-13ms`. The walk variable is
left alone, since `minor_index_is_major` counts indices from `first_major` and
both operands have to stay on the walk's own grid.
The two narrow-y-title cases were calibrated on the defect -- the bogus `-55.5a`
was a six-character label, and its width is what spent the chrome allowance and
made the titled and untitled frames comparable. They are re-seated on a
milli-scale range, whose `-200m` is wide for a real reason, and the zero-width
strip the frame comparison depends on is now asserted rather than assumed.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Breaking: Series::gather emits x relative to x0() and takes a GatherMode;
consumers reconstruct absolute x in f64 before mapping (series.hpp documents
the contract).
Bugs, each pinned by a fail-before regression test:
- render: f32 staging quantised epoch-time x into 128 px columns; every
data-space draw now stages to_space(x) - to_space(origin) with the origin
folded into the offset uniform in f64 (epoch/zero-origin twins rasterise
identically)
- ticks: major test was ULP-fragile and blanked epoch axes; majors are an
integer-index test and are never truncated by the minor cap
- gather: LOD envelope emitted buckets straddling [begin,end); ceil/floor
bucket edges + raw lead/trail spans
- live follow: log x axes held a linear span and zoomed every frame; span and
offset now live in axis space (plot + both figure link-group paths)
- input: a zero-notch wheel disarmed auto_scale on every axis; dy==0 pans x,
factor == 1 / inf refused in wheel and drag zoom
- render: the single text flush painted legend names over the crosshair
readout panel; two batches, under flushed before the panel
- data: NaN dropped from min/max unless it seeded the fold; non-finite
samples are now excluded from every aggregate and from cached bounds
Robustness: viewport normalisation (no clamp UB), non-finite range refusal,
pyramid level cap at 57 (no shift/div UB through public gather), rounded ring
capacity documented + pre-sized, GL blend func and UNPACK_ALIGNMENT
save/restore, Renderer::release_gl() teardown, u64 buffer epochs, annotation
captions clamped, button-aware GLFW row capture, cached figure row rects (no
per-event layout), ruler-pair measurement refused, span-nonfinite guards in
axis_ends.
Features: XY series (sorted x, binary-search neighbours/snap, LOD over sample
index); StreamSeries::freeze(); ArraySeries::push(); per-trace dash and
markers (scatter at width 0) with auto or literal stride; GatherMode
Envelope/Nearest/Mean via bucket_sum/sumsq; Style::line_aa_px; per-glyph text
colour (readout values in trace colour); wheel-dx x pan; arrow-key pan;
Escape cancels a drag and restores captured ranges; modifier-masked box zoom
(Shift both, Ctrl x, Alt y); double-click reset via PointerEvent::time_s;
ImGui key repeat unified; pinch gestures on Qt and GTK; pixelDelta wheel path
and DevicePixelRatioChange handling; GNUInstallDirs, SOVERSION,
SameMinorVersion, generated plot/version.hpp, relocatable plot.pc, licence
install, FILES_MATCHING, GitHub Actions CI (debug/coverage/asan).
Suite 283 -> 350 cases, 0 failed; coverage 93.9% (3730/3971) over 24 files,
floor 80/90 held; ASAN preset suite green; all four demos run headless (the
GTK scripted-resize check needs a window manager and fails identically on the
parent commit); readme_main.cpp committed and compiles with the README
command; pkg-config and find_package consumption verified from a relocated
install prefix.
The repository had no licence at all, so every source was all-rights-reserved
by default. Add the verbatim MIT text at LICENSE (Copyright (c) 2026 Martino
Ferrari) and a two-line SPDX header to each of the 113 first-party sources --
48 include/plot, 26 src, 10 adapters, 5 examples, 21 tests, 3 tools -- so the
grant travels with each file rather than relying on the root document alone.
Scripts keep their shebang on line 1; the SPDX lines follow it. Genuinely
vendored code is untouched: third_party/stb_truetype.h carries no header of
ours. src/render/embedded_mono_font.cpp is generated, so tools/fonts/gen_atlas.py
emit() now writes the two lines into its header comment and the file was
regenerated -- gen_atlas.py --check passes and the regeneration adds only those
comment lines to the previously committed file.
README's provenance section now states MIT and links LICENSE.
No code, test or public API change.
Martino Ferrari