The offset of a following group was clamped to `retained` -- measured from the newest sample -- so
a pan (or a zoom-in anchored near an edge) could put the window's *right* edge exactly on the oldest
retained sample. That leaves the window's entire span to its left over data the scope never had: an
empty margin as wide as the view. The bound is about the whole window, so it is `retained - span` --
but only while the window *can* sit on the data. When the members retain less than a window's worth
(a ring still filling, or one just trimmed) nothing avoids a margin, and the older placement is the
honest one and stays: right edge on the newest sample, the shortfall on the left.
Test: a_following_group_keeps_its_whole_window_on_the_data -- asks to scroll ten spans past the
oldest sample and asserts the window is still a window, with its left edge on the data. The
existing `a_following_log_group_holds_decades` codified the old bound (`max == edge/10` after asking
for a decade of pan with far less than that retained); its log-space subject is unchanged and the
offset assertion is now the invariant above.
`Style::marker_below_samples` (50 by default, `0` for never) draws a `marker_px` dot on every
*raw* sample when the visible window holds at most that many, in the trace's own colour. Zoomed
in far enough to see individual samples, the polyline between them stops being the shape a reader
is looking at -- a handful of points across a whole panel ARE the picture -- and a dot makes each
one a place rather than a bend in a line. Level 0 only: above it the geometry is pyramid buckets,
which are not points anyone can find.
Test: a_sparse_window_marks_its_samples -- the same flat series at ten samples and at a hundred.
Ten gives exactly ten dots, evenly spaced (their centres are checked against the panel's own
step, so "they are the samples" is asserted rather than "something was painted"); a hundred is
past the threshold and gives none. The dots *group* into runs of columns (a marker is `marker_px`
wide), which is how the test reads one marker per sample -- counting columns read three.
Subdivisions used to be drawn exactly like the labelled lines -- same width, same
opacity -- so a plot dense enough to need them read as two competing sets of ticks.
The minor class is now three things the style states explicitly:
- grid_minor_width 1.0 -> 0.75, a sub-pixel logical width. At 1x that is expressed as
reduced coverage through the anti-aliased ramp; on a HiDPI display the line is
literally narrower.
- grid_minor_dash_on/_off (new, 3/3): dashed by default, off == 0 draws it solid, the
same convention as the crosshair's and a trace's dash. The dash is a fragment-shader
discard, so no geometry is added -- the vertices are the line either way.
- grid_minor carries alpha (0x1C2126 at 50%), and the line shader applies u_color.a,
so it blends into the background instead of sitting on it.
Together that is about a fifth of the ink a major line leaves along its length, which
is what gives the eye one grid to read instead of two. The major class is untouched:
it stays the structure.
Tests: a new pixel test (the_minor_grid_is_thinner_dashed_and_dimmer_than_the_major)
asserts a major column is inked top-to-bottom while a minor one alternates, and that
the minor's ink sits closer to the background than the major's. Three existing tests
counted the minor class as "most of eight rows" of its exact colour; two now take
their floor from the style (minor_line_ink: width x alpha x duty), and the width test
states the dash and alpha away because widths are its subject. 361 cases, 0 failed.
Renderer::draw_traces picked the sample window with (x - x0()) / dx(), and dx() is
documented as a *nominal* spacing -- for a series whose x is a streamed timestamp it
is only the mean of the retained window. The window it computed therefore landed
inside the visible range, and the two end segments, the ones that enter and leave the
frame, were never emitted: the left and right margins of a zoomed-in view came out
empty. A wide enough drift dropped the trace entirely (last <= first).
It asks Series::neighbours() now -- a binary search over the real x, the same call the
crosshair reads through, costing the same. A uniform series answers the same question
through the same call, so it is one path. dx is still read for the samples-per-pixel
density estimate, where a nominal spacing is exactly right.
Test: a_sparse_window_between_samples_still_inks_both_margins -- a series whose dx()
lies, with the window strictly between two samples, so nothing inside the window is
sampled and only the crossing segments can ink it. With the grid walk reverted it
stages nothing at all (visible=0, gathered=0, covered=0/24); with the fix it stages the
three bracketing samples and covers 24/24 columns.
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