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name	description
md2img	This skill should be used when the user wants to render a Markdown document (containing Mermaid diagrams, LaTeX math formulas, or rich formatting) into a PNG image.

md2img

Render Markdown documents into high-quality PNG images with full support for Mermaid diagrams, LaTeX math formulas, code syntax highlighting, and GFM tables.

Features

Mermaid diagrams: flowchart, sequence, class, state, gantt, pie, etc. (rendered in-browser via mermaid.js)
LaTeX math: inline $...$ and block $$...$$ / \[...\] (via KaTeX)
GFM syntax: tables, task lists, strikethrough, code blocks
Code highlighting: via highlight.js CSS
Dark/Light theme: auto-detects system preference, or override with --dark/--light
Paper sizes: A4 (default) or Letter, 2x DPI for crisp output
Cross-platform: Windows (Chrome/Edge) and Linux (Chrome/Chromium)

Usage Workflow

Write the Markdown content to a temporary .md file
Run the render script
Present the generated PNG to the user

Command

node <skill_dir>/scripts/render.js <input.md> [output.png] [--paper=a4|letter] [--dark|--light]

Parameters

Parameter	Default	Description
`input.md`	(required)	Input Markdown file path
`output.png`	`<input>.png`	Output PNG file path
`--paper`	`a4`	Paper size: `a4` (794px) or `letter` (816px)
`--dark`	auto	Force dark theme
`--light`	auto	Force light theme

Examples

# Basic usage
node render.js readme.md

# Specify output path and paper size
node render.js slides.md output.png --paper=letter

# Force dark theme (for dark background images)
node render.js notes.md card.png --dark

Environment Setup

Windows (current machine)

Already configured. Uses local Edge/Chrome via puppeteer-core.

Linux (headless server)

On Linux servers without a GUI browser, install Chromium:

# Option 1: Install puppeteer (auto-downloads Chromium)
cd skills/md2img/scripts
npm install puppeteer
npx puppeteer browsers install chrome

# Option 2: Install system Chromium
# Ubuntu/Debian:
sudo apt install -y chromium-browser
# CentOS/RHEL:
sudo yum install -y chromium
# Alpine:
apk add chromium

# Option 3: Set CHROME_PATH env variable
export CHROME_PATH=/usr/bin/chromium-browser

Linux headless prerequisites:

# Ubuntu/Debian — required shared libraries
sudo apt install -y libnss3 libatk1.0-0 libatk-bridge2.0-0 libcups2 libdrm2 \
  libxkbcommon0 libxcomposite1 libxdamage1 libxrandr2 libgbm1 libasound2 \
  libpango-1.0-0 libcairo2 libxshmfence1

# Alpine
apk add nss atk cups-libs libdrm libxkbcommon libxcomposite libxdamage \
  libxrandr mesa-gbm alsa-lib pango cairo

Emoji font support (Linux):

Linux默认不支持emoji渲染，需安装emoji字体：

# Ubuntu/Debian:
sudo apt install -y fonts-noto-color-emoji

# Fedora:
sudo dnf install -y google-noto-emoji-color-fonts

# Arch/Manjaro:
sudo pacman -S noto-fonts-emoji

# Verify:
fc-list | grep -i emoji
fc-match "😀"  # Should return: NotoColorEmoji.ttf

Docker deployment

FROM node:20-slim

# Install Chromium dependencies and fonts (including emoji support)
RUN apt-get update && apt-get install -y \
    chromium \
    fonts-noto-cjk \
    fonts-noto-color-emoji \
    --no-install-recommends && \
    rm -rf /var/lib/apt/lists/*

# Set CHROME_PATH so puppeteer-core finds it
ENV CHROME_PATH=/usr/bin/chromium
ENV PUPPETEER_SKIP_CHROMIUM_DOWNLOAD=true

WORKDIR /app
COPY scripts/package.json scripts/render.js ./
RUN npm install --production

ENTRYPOINT ["node", "render.js"]

Technical Details

Markdown parsing: marked v12 with custom renderer for mermaid code blocks
LaTeX rendering: KaTeX server-side pre-render (no browser-side JS needed)
Mermaid rendering: mermaid.js browser-side rendering via CDN (mermaid requires DOM API, cannot render in Node.js)
Browser automation: puppeteer-core (Windows, uses local Edge/Chrome) or puppeteer (Linux, bundled Chromium), with auto-detection
Output: 2x DPI PNG (A4: 1588px wide, Letter: 1632px wide)
Font stack: System fonts + CJK fallback (PingFang SC, Microsoft YaHei, Noto Sans SC)

Troubleshooting

Issue	Solution
"No Chrome/Edge/Chromium found"	Install Chrome/Chromium or run `npm install puppeteer`
Chinese characters missing on Linux	Install CJK fonts: `apt install fonts-noto-cjk`
Emoji显示为方框□ on Linux	Install emoji fonts: `apt install fonts-noto-color-emoji`
`/dev/shm` errors on Linux	Use `--disable-dev-shm-usage` (already included)
Puppeteer download timeout in China	Set mirror: `PUPPETEER_DOWNLOAD_BASE_URL=https://cdn.npmmirror.com/binaries/chrome-for-testing npx puppeteer browsers install chrome`
Screenshot blank/white	Ensure `waitUntil: 'networkidle0'` completes; check font availability

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