presentation-factory-html-to-pdf

name	presentation-factory-html-to-pdf
description	Renders each composed slide HTML to a single PDF page at 1920×1080, then merges them into deck.pdf. Uses headless Chromium via Bash. Validates the output has the right page count and resolution.
type	skill
plugin	presentation-factory
tags	["type/skill","plugin/presentation-factory","scope/specialty","topic/pdf-export"]
status	active

When to invoke

Called from the Ship stage orchestrator after the user has approved the composed slides.

Required context

Toolchain: ../../references/presentation-factory-toolchain.md. Foundations: ../../references/presentation-factory-foundations.md.

What this skill does

Stage 1: Verify dependencies

Bash check:

which chromium || which google-chrome || which chrome
which pdftk || which python3 # python3 + pypdf as fallback

If neither Chromium nor Chrome is found, surface the issue. macOS install:

brew install --cask chromium

Stage 2: Render each slide to a single-page PDF

For each slides/NN-template.html in the WIP folder:

chromium --headless --disable-gpu \
  --no-margins \
  --print-to-pdf="WIP/[deck]/_pdf/slide-NN.pdf" \
  --virtual-time-budget=3000 \
  --window-size=1920,1080 \
  --hide-scrollbars \
  --run-all-compositor-stages-before-draw \
  "file://$PWD/WIP/[deck]/slides/NN-template.html"

Notes:

• --virtual-time-budget=3000 waits 3 seconds for any JS (the chart template uses vanilla JS to render the SVG bars)
• --no-margins prevents Chrome's default print margins
• --window-size=1920,1080 matches the slide canvas exactly
• --hide-scrollbars removes any scrollbar artifacts

Stage 3: Adjust the page size

Chromium's default --print-to-pdf uses letter size. The HTML body is 1920×1080 px. With CSS @page { size: ... } in the template, we can force exact dimensions. The slalom.css tokens already include the 1920×1080 body sizing.

Add to the composed slide HTML at compose time (in the composer skill's pass — already covered in the composer), inside <style>:

@page {
  size: 1920px 1080px;
  margin: 0;
}

If pages still come out wrong, fall back to Puppeteer / Playwright via Node script:

// puppeteer-render.js
const puppeteer = require('puppeteer');
(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.setViewport({ width: 1920, height: 1080, deviceScaleFactor: 2 });
  await page.goto(`file://${slidePath}`, { waitUntil: 'networkidle0' });
  await page.pdf({
    path: outPath,
    width: '1920px',
    height: '1080px',
    printBackground: true,
    margin: { top: 0, right: 0, bottom: 0, left: 0 },
  });
  await browser.close();
})();

Stage 4: Merge slide PDFs into deck.pdf

cd WIP/[deck]/_pdf
pdftk slide-*.pdf cat output ../deck.pdf

Fallback if pdftk not installed:

# merge.py
from pypdf import PdfWriter
writer = PdfWriter()
for f in sorted(os.listdir("WIP/[deck]/_pdf")):
    writer.append(f"WIP/[deck]/_pdf/{f}")
writer.write("WIP/[deck]/deck.pdf")

Stage 5: Validate output

# Count pages — must match slide count
pdfinfo WIP/[deck]/deck.pdf | grep "Pages:"
# Or via Python: PdfReader("deck.pdf").pages length

Also: visually spot-check the first slide by extracting its rendered preview:

pdftoppm -f 1 -l 1 -png -r 96 WIP/[deck]/deck.pdf WIP/[deck]/_preview
# Produces _preview-01.png — show to user as a sanity check

Stage 6: Clean up

After the merged deck.pdf is in place, remove the per-slide intermediate PDFs in _pdf/ to keep WIP tidy (or leave them for debugging — config flag).

Output

File	Path
Merged deck	WIP/[deck]/deck.pdf
Preview thumbnail of slide 1	WIP/[deck]/_preview-01.png (optional)
Render log	WIP/[deck]/render.log

Anti-patterns

• Don't rely on --print-to-pdf page dimensions defaulting correctly — always set @page in CSS and viewport in the headless command
• Don't skip the virtual-time-budget — JS-rendered slides (chart template) will appear blank otherwise
• Don't merge without sorting — slide-*.pdf glob sorts alphabetically; using NN-prefixed names ensures correct order
• Don't delete the slide HTML files after PDF export — they're needed for PPTX conversion (next skill)