[andiwand]

🤖 Generated with Claude Code

Refs #764.

Summary

This implements decision 6 of docs/design/lazy-loading.md (#1249): a sheet is the ruler and a <table> for each chunk of rows. With the 500 K-cell sheet of efficiency-big-1.ods in headless Chrome:

	first frame	layout	renderer RSS
before	7.0 s	2.6 s	2.8 GB
after	4.0 s	1.3 s	2.7 GB

About 2 s of the rest is viewport.js, which existed before this change. It sets the body zoom twice to probe text-size adjustment, and each set restyles and relays out the whole document. That is a follow-up.

Writer (translate_sheet)

• div.odr-sheet takes the sheet's attributes, and the ruler is a sticky table.odr-sheet-head.
• A chunk holds up to 256 rows or 4,096 cells, at least 8 rows, and ends only where no rowspan is open.
• Each chunk states contain-intrinsic-height: auto from its rows' heights, 20px where a row states none.
• The first chunk of a sheet with shapes is data-odr-chunk-held.
• Widths: every table states the sheet width (--odr-sheet-width), and the gutter and every column are in px, so table-layout: fixed takes the widths from the cols alone.
  • Without that width, the browser's automatic table layout shrank each column of an over-wide sheet to what its own cells hold, so the ruler and the chunks did not line up. This showed in the 500 K-cell sheet.
  • A column that states no width now gets 7.5px for each character of its longest text in the first 1,000 rows, plus 14px, clamped to 4–60 characters. A cell that wraps counts its longest word.

Scripts

• spreadsheet.js reads the rows of every chunk.
  • A sort refills the chunks with the same counts.
  • Row edits work in the chunk of the row, and a chunk with no row left goes.
  • Column edits change every table and --odr-sheet-width. A new column is 64px.
  • A reflow in a far chunk waits for the chunk's odr-chunk-near event.
• viewport.js raises odr-chunk-near, skips held chunks, and gets odr.chunks.show and observe. The editor's place and odr.search show the chunk before they measure or scroll.

References. Every sheet page changes. I checked the change by screenshot A/B:

• Public: 48 of 83 pages differ by under 0.4% after a blur.
• Private: 147 of 229.
• The larger differences are columns that took their content's width before and now take the estimate. Three cases:
  • sample.xlsx: column D is wider.
  • Konzentration.xls: the headers wrap where they did before.
  • ruski.xlsx: a long number in a wide file font spills past its column. That is the limit of an estimate that does not know the font.

Copied to output main with the pins advanced:

• public fc8d7fb: 83 pages and 6 resources
• private 434d410: 272 pages and 5 resources

spreadsheet.js and sheet-editing.js also carry earlier PRs' changes that the references had missed.

Test

• All 2,529 C++ tests pass. The four html tests on sheet style classes now expect the width classes before the cell classes.
• All 20 pages of test/browser/sheet pass. That includes the new chunks.html (15 checks): positions across chunks, row edits into and out of a chunk, an emptied chunk, a column in every table, a deferred spill, and a sort over chunks. The text, plaintext, viewport, bridge and annotation pages pass too.
• Screenshots of the 500 K-cell sheet in the middle and of a csv across a chunk boundary: the ruler and the chunks line up.

Review fixes

• html.a_sheet_ends_a_chunk_only_where_no_merge_is_open: the writer had no C++ test for where a chunk ends. A sheet of 300 rows with a merge over rows 251 to 260 checks that the first chunk takes the merge, and that the second chunk holds the 40 rows left and states 800px.
• The comment of fods_columns said that a column without a width is exactly its content's width. It now says that such a column takes the width of its longest text.
• spreadsheet.js declared odr below the helpers that read it. It now comes first.
• Checked again: 963 C++ tests for html, sheets, text, pdf and edits pass. All pages of test/browser sheet, text, plaintext, viewport, bridge and annotation pass, with the formula pages run against the wasm module.