Add lt_export() to save tables as PDF or PNG

[yihui]

What

New lt_export(x, output = 'lt.pdf', crop = TRUE, padding = 8, ...) renders an lt_tbl in headless Chromium and writes it to a file. Format follows the output extension: .pdf → vector PDF (Chromium print-to-PDF), otherwise PNG.

Cropping

By default the output is cropped tight to the table (no surrounding page whitespace). A preliminary browser_dom() pass runs lt.js and measures the body's scroll size — this matters because the caption's border-top and footer spacing extend past the <table> border-box, so measuring the table box alone undercounts the height.

• PDF: an @page{size:...} rule sets the page box exactly → single page, dep-free. (Measuring the table box was the cause of the two-page penguins output.)
• PNG: Chromium's --screenshot size equals the window size and can't go below Chromium's minimum window / reserved-chrome height, which scales overflowing content. So we render onto a generous window (table unscaled, top-left) and crop to the exact box with magick. Without magick, PNG falls back to the full page with a warning.

SVG is not supported — Chromium cannot export a rendered page as SVG; PDF is the vector option.

Tests

tests/test-ci/test-js.R (browser-gated): PDF+PNG written with correct magic bytes, a large table crops to one PDF page (regression guard), and the cropped PNG matches the measured content box exactly (magick-gated).

🤖 Generated with Claude Code

[yihui]

should lt_html() be merged into lt_export()? lt_html() basically exports the table to html (without relying on js to render the table)

[yihui]

Re: merging lt_html() into lt_export() — I kept lt_html() but wired it into lt_export() so there's now one file-export entry point:

• lt_export(x, 'tbl.html') writes a static HTML table by delegating to lt_html() (no browser needed).
• lt_export(x, 'tbl.pdf'|'tbl.png') renders via headless Chromium.

I left lt_html() as its own exported function because it returns the HTML string rather than writing a file, and it's used internally (knit_print / record_print / the lt.lt_html option / tests) — those need the string, not a file. So lt_export() is the 'write to disk' front door, lt_html() is the 'give me the markup' engine. If you'd rather fully fold it in (e.g. drop lt_html() and have callers use format()/an internal helper), I can do that — let me know.

[yihui]

Done in 9581b89:

• Unexported lt_html() — now an internal helper. lt_export() is the only public export API. lt_html() still renders the static table and still backs the lt.lt_html option (knit_print/record_print); its method/css args are reachable via lt_export(x, 'file.html', method=, css=). Moved the Global-option docs onto lt_export().
• Dropped height — height is always derived from content at the chosen width; width alone remains, honored whether crop is TRUE or FALSE.