Skip to content
Meltemi docs

Ask the docs

Ask a question in your own words: the answer is written from the portal's pages only, and names the pages it used.

0 of 500 characters

Your question is sent to Cloudflare Workers AI to be answered and is not stored. Answers can be wrong: check the sources. Privacy notice

Answers run on Cloudflare's free allowance, about four hundred a day for everyone.

Español

0025. Export profiles, and PNG and PDF from the installed browser

Status: accepted (export-png-pdf change, 11 October 2026)

Context

Section titled “Context”

The proposal’s export block is a reproducible delivery profile: each profile describes format, dimensions, resources, font treatment and animation behaviour. PNG serves documents and slides with configurable resolution and optional transparency; PDF serves sheets and documents with defined dimensions, checked fonts, vectors and links; a slide may carry a frame and a link to the walkthrough. Playwright and Chromium are the proposal’s candidates for captures and PDF printing, and reproducibility is promised within a pinned environment, not across systems. Edge and Chrome are installed where the product is built; the approved plan drives the installed browser.

Decision

Section titled “Decision”
  • Profiles compile. export <id> for <target> { … } becomes Document.exports, every option checked against the format and the target, with export.* diagnostics. Video options are compiled now; the encoder comes with change 17. No block of the language is parse-only any more, so block.unsupported is gone.
  • The browser draws PNG and PDF. The SVG the exporter writes, with embedded fonts, is drawn by the installed Chromium browser: screenshots for PNG (device scale factor, transparent default background when asked) and print-to-PDF for PDF (CSS page of the picture’s size, tagged, vectors, fonts and links kept). The same engine that displays SVG in browsers draws the files, so they look like the SVG.
  • A small DevTools client, no dependency. @meltemi/diagrams-capture speaks the DevTools protocol over --remote-debugging-pipe (NUL-separated JSON on file descriptors 3 and 4), with the switches that keep Edge from relaunching itself. It is plain JavaScript modules so that a plain node runs it: the synchronous command line calls a child process, the editor calls it directly.
  • One production path. produceExport and profileRequest in the editor’s Node entry turn a request into SVG or HTML text or a capture job; the command line and VS Code only differ in how they write the results.
  • Links. url on elements and entities, and a profile’s link for the whole picture, written as SVG <a> elements; only http:, https:, mailto: and relative URLs are accepted.

Alternatives considered

Section titled “Alternatives considered”
  • Playwright. Approved and used by the tests, but a large runtime dependency for two calls; the protocol subset needed is small.
  • A rasterizer and a PDF writer of our own. Exact control, but text shaping, fonts, images and anti-aliasing would have to match the browser’s SVG rendering; the browser is the reference.
  • resvg or similar. Would need a native or WebAssembly download that was not approved.

Consequences

Section titled “Consequences”
  • PNG and PDF need a Chromium browser on the machine (or MELTEMI_BROWSER); SVG and HTML need none.
  • Video exports (change 17) capture frames the same way and encode them with the system FFmpeg.
  • The verification matrix (change 23) records the browser version each export names.