Final whole-branch review fixes.
1 (Important). Plot::measurement() cached on (series pointer, sample count)
only, so a saturated StreamSeries -- whose size() stays pinned while x0()
advances every acquire() -- froze its readout on the first saturated frame
until a cursor moved. The cache key now carries the series' x0() (new
MeasureSlot::last_x0), so a sliding window recomputes and a static series
still does not: asserted with a new macro-gated counter hook
(plot/detail/measure_count.hpp, PLOT_COUNT_MEASURE_RECOMPUTES, wired like the
pyramid and ring counters, absent from the release library). New case
saturated_stream_measurement_tracks_the_sliding_window: saturated ring,
stationary cursors, ramp in absolute x -- zero recomputes for repeated reads
with nothing moving, one per acquire while it slides.
2-3, 9. Spec: 4.3 described a GL_LINE_STRIP path that does not exist (there is
one rasteriser -- instanced anti-aliased quads -- and dense_threshold_spp
selects the gather level, not a primitive); 8 named a PLOT_GL_CHECK() macro
that exists nowhere, and stated no exception policy. The table, the field's
comment and 8 now describe the real gather-level threshold, the real
glGetError() drain plus the stores' drop-to-orphan fallbacks, and the real
policy: library failures return Status/bool, allocating entry points propagate
std::bad_alloc.
4. The frame handed back neither GL_UNPACK_ALIGNMENT (init() sets 1 for the
atlas) nor the clear colour (queried once with a new glGetFloatv entry).
end_frame() restores both and renderer.hpp lists them in the residue
contract.
5. draw() kept a host TextBackend for layout while drawing with its own font.
The renderer now installs its font unconditionally -- strips and labels measure
and draw with one backend -- with a debug-build diagnostic if a different one
was set, and Plot::set_text_backend() is documented as the no-renderer path.
New case renderer_measures_the_labels_it_draws asserts layout, measuring and
the drawn label's ink agree.
6-10. draw()'s style overwrite stated at the call site; the load-sensitive
wall-clock bound in test_measure.cpp replaced by a counter assertion (same
interval, same fold count over a 512x length ratio); dump_frame_ppm drops
noexcept and says why it may allocate; error.txt ignored (not this project's,
not generated here) rather than deleted.
Verified: debug and release build clean (-Wall -Wextra -Wpedantic -Wconversion
-Wshadow), 4/4 ctest entries pass, 130 cases pass (was 127), umbrella and
header self-containment checks pass, and no counter symbol in the release
archive.
Findings from the review of the sliding-window change:
- A level >= 1 gather emitted only complete, wholly-retained buckets, so the
geometry stopped at the last bucket boundary inside the range: the newest
samples of a live window -- up to `span - 1` of them, about a pixel at the
level level_for() picks -- were not drawn, on the right edge, which is the
part of a scrolling trace that gets watched, and the oldest retained samples
fell outside the geometry too (the level-1 gather of a sliding window started
51 samples in). The two partial edge buckets are now gathered as raw samples
through copy_raw() and bracketed around the envelope -- the same exactness
split reduce/sum/sumsq already use -- so the emitted geometry spans the
requested range exactly. The pyramid still stores no partial bucket, so append
stays amortised O(1); at 1 MS/s the demo stages 511 extra sub-pixel segments
and still draws at 1.05 ms/frame, and the screenshot's trace now reaches one
column further at each end.
- `drop_before`'s doc claimed a no-op "for an empty pyramid": false, and
backwards -- the restart branch is exactly what an empty pyramid hits, which is
what StreamSeries::acquire() depends on when the ring saturated before the
first acquire. The precondition is `absolute_sample <= window_base()`, and the
restart is documented as what it is.
- The pyramid's memory figure was 3x optimistic: an entry is 24 bytes (MinMax
plus the exact sum/sumsq doubles), so level 0 costs 0.375n bytes and the whole
pyramid ~0.75n -- about 19% of 4-byte raw samples, not the 6% a min/max-only
index would cost. Corrected in the header, spec 4.2 and 4.5, with the trade
stated (the doubles buy O(log n) sum/mean/RMS/integral from whole buckets),
and the plan's Task 3 sketch no longer describes per-level prefix sums, a
level() span or an unaligned-end widening that does not exist.
Tests: `gather_at_a_lod_level_reaches_both_ends_of_the_window` pins that the
first and last emitted points are the oldest and newest retained samples -- with
spike values no bucket envelope can produce -- at level 1, at the level a dense
view picks, and for a static series whose end is unaligned. It fails against the
previous commit (first point at the first whole bucket), and so does the sliding
gather mapping check, which now accounts for the raw edge pairs.
Frame cost was O(capacity x levels) once the ring saturated: acquire() saw the
window base move (it always moves once the ring wraps), cleared the pyramid and
re-appended all 1,048,576 retained samples, and append() walked every live level
with no early stop -- 13,647,936 bucket merges and 73.8 ms per frame at a
1M-sample window, scaling with the window, which is what capped the 1 MS/s demo
at 32-58 ms/frame while it was still filling.
Index the pyramid in absolute bucket space instead. Level l bucket k covers the
samples [k * (kBucket << l), (k + 1) * (kBucket << l)), so a bucket's span never
depends on where the window starts and the window can slide over the aggregate
instead of forcing it to be rebuilt. Each level keeps its complete buckets in a
deque plus the absolute base of its first entry; append() folds a sample into the
single in-progress level-0 bucket and, only when that bucket completes, cascades
upward, stopping at the first level that gains no new entry; a new drop_before()
slides the window by discarding leading buckets and remembers where the window
begins. acquire() is now: drop to the new base, then append exactly what was
produced -- 256 merges and 0.034 ms per frame for 8192 new samples, independent
of the window, and memory bounded by the window (32,767 entries after 50M samples
through a 1M ring, the same as after 10M). A producer that laps the consumer by
more than capacity() between two acquires restarts the window rather than
splicing a gap.
Interface: `level(l) -> std::span<const MinMax>` cannot survive a ring and is
replaced by level_base/level_size/bucket in absolute bucket coordinates, plus
window_base/window_end/drop_before. The *_buckets queries stay in window
coordinates (index 0 = oldest retained sample), so Series keeps its window
semantics for callers; its exactness split now aligns in absolute space
(window_base() + the ceil/floor) because the bucket grid is absolute. The sums
move from per-level prefix sums to per-bucket ones -- the only representation a
sliding front can keep exact -- and StreamSeries::y_bounds() becomes
reduce(0, size()), exact in O(log n + kBucket) per frame instead of a scan of the
window. The pyramid owns the published window now, so there is no second copy of
base/end to keep in step, and gather() emits only buckets that are both complete
and wholly retained.
Tests: test-only merge counters (mirroring PLOT_PYRAMID_COUNT_COVERS, absent from
every non-test build) pin an acquire proportional to production and independent
of capacity, an append cost amortised over 16 live levels, and bounded memory;
brute-force checks pin absolute bucket aggregates across slides, sliding-window
reduce/sum/sumsq over unaligned ranges, and the level-1 gather mapping. The demo
now draws 946 samples/px at 1.03 ms/frame (967 fps) where the saturated window
cost 54.96 ms/frame (18 fps).
Martino Ferrari