Martino Ferrari
0ac5d47fa6
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).