XLSX: drawing-only sheets lay out columns with a hardcoded 7px digit width, so pictures are 8% distorted and a 2-page sheet collapses to 1

[developer0hye]

Summary

empty_sheet_context() (crates/office2pdf/src/parser/xlsx.rs:212) hardcodes
max_digit_width_px: 7.0 and normal_font: None, so anchored_image and
anchored_text_box never see the workbook's Normal font on a sheet whose <sheetData/>
is empty. Every such sheet is laid out on 44.2575pt columns, which is exactly
column_width_to_pt(8.43, 7.0).

These workbooks declare Calibri 11, for which office2pdf's own
max_digit_width_px_for_normal_font returns 8.0 px → 50.58pt. The drawing-only sheets are
therefore laid out 12.5% narrower than the converter's own font model says they should be,
with no GT needed to see the inconsistency.

Measured

Column width solved from anchor geometry on two independent fixtures — two equations, no
global scale factor involved:

fixture	anchors	solve	result
WithDrawing	clock.jpg twoCellAnchor col 0→3; tomcat.png col 8→10 + 19050 EMU	3C = 132.7725, 2C + 19050/12700 = 90.015	C = 44.2575, offset unscaled
WithTextBox	WithTextBox anchor col 2→7 + 21.75pt	5C + 21.75 = 243.04	C = 44.2575

	expected (Calibri 11, 8.0 px)	office2pdf (hardcoded 7.0 px)
column width	50.58pt	44.2575pt (−12.5%)
columns fitting A4's 494.5pt printable width	9	11
WithDrawing pages	2	1
clock.jpg rendered size (source 192×176, a:ext 144×132pt)	aspect 1.091	132.77 × 132pt, aspect 1.006 (−8%)

WithDrawing's content reaches column 11, so the printout collapses from two pages to one
and the two pictures Excel splits across the horizontal page break (tomcat.png,
santa.wmf) are drawn whole on page 1. Pictures are also squashed horizontally: only the
width comes from the bad column model, while the height comes from row heights, so the
aspect ratio is distorted by 8%.

This is not the fit-to-width path: WithDrawing, WithTextBox and WithChart carry no
<pageSetup> at all, so sheets_fitting_to_page never matches and no fit scale is applied.

Reproduction

cargo run -p office2pdf-cli -- tests/fixtures/xlsx/poi/WithDrawing.xlsx -o out.pdf
pdfinfo out.pdf | grep Pages    # 1; Excel prints 2
mutool draw -F trace -o - out.pdf 1 | grep -i image

Expected

A sheet with no cells still resolves its drawing anchors against the workbook's Normal font,
producing the same column metric as a sheet that happens to have cells in it.

Actual

empty_sheet_context() substitutes a 7.0 px digit width and drops the Normal font, so every
drawing-only sheet is 12.5% narrow, pictures are 8% aspect-distorted, and a two-page sheet
collapses to one.

Related: #460, #473

Found in the 2026-07-29 full-corpus visual audit at c1adfbd (native Office GT, 150 DPI, mutool-trace geometry).

Visual comparison

Compare

GT left, office2pdf right, 150 DPI, same page.

[developer0hye]

Fixed by #716. Drawing-only sheets now derive their column metric from the workbook Normal font through the same helper populated sheets use (resolve_max_digit_width_px) instead of the hardcoded 7px: WithDrawing's columns solve to exactly 50.58pt from three independent anchors (was 44.2575pt), tomcat.png's x error shrinks from −69.5pt to −19.0pt and clock.jpg's width error from −16.5% to −4.6% against a fresh local Excel-for-Mac GT export. Populated-sheet output is byte-identical.

Every residual on the fresh GT comparison has its own open issue: #621 (Calibri metric-table gap, with a new Mac-measurement data point commented there), #713 (drawing extents never split into page-columns — the page-count delta), #714 (declared <cols> widths ignored on drawing-only sheets, found by one-factor probe), #715 (Excel recomputes default row heights from the Normal font), #656 (text-box line pitch doubling).