grid_of evaluated the whole grid roughly three times per frame:
compute_col_widths walked every cell for its text, then every cell again for the
column totals it must size, and grid_of then evaluated the window a third time.
Every result was discarded at the end of the frame.
ui/viewport.rs::grid_body is now the one walk. It evaluates each cell once and
derives all three answers from that value -- widen the column, add to the
column's sum, and if the position is inside the requested window keep the
CellValue for cell_display to dress. compute_col_widths survives as grid_body
with an empty window, because the keypress path wants widths and no cells, and
two width rules would be the disease improvise-edp names.
MEASURED, orchestrator's machine, cargo bench --bench grid_projection, before
and after:
typical (400 cells) 1.840ms -> 0.687ms
large (9,600) 172.6ms -> 50.0ms
18k (gotcha 41) 294.4ms -> 95.2ms
pathological (90,000) 4.481s -> 1.320s
About 3x, which is the number of passes removed -- the shape the acceptance
criterion asked for rather than a speedup argued from the structure.
Three things the ticket did not predict.
The benchmark's col_widths column now measures something ELSE. It read 45-47%
and now reads 64-82%, which looks like a regression and is the opposite:
compute_col_widths IS the fused walk, so its share rose while the frame fell by
two thirds. A ratio whose denominator moved is not comparable across the change,
and the benchmark now says so.
The windowing ratio did not improve, and that is correct: the pass that remains
is exactly the one a viewport cannot narrow. improvise-i5tk's decline stands and
the two findings are now cleanly separated.
It is not solved, only three times cheaper -- 18k cells is still 95ms, 5.7
frames. The next lever is caching ACROSS frames.
Guard: a_window_narrows_the_cells_and_neither_the_totals_nor_the_widths. Fusing
three consumers into one walk creates a hazard the separate passes did not have,
and the natural "optimisation" (iterate rows rather than 0..row_count) makes a
column total the sum of the visible rows, silently. Watched fail with
left: [1.0] against right: [300021.0]. All 1469 pre-existing tests unchanged,
which is also the evidence the outputs did not move.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FC2jVn8Au7E9JPkw6bwXXH
Edward Langley
822547a332