LaTeX Comment Preview

Preview LaTeX math written inside Python comments — # line comments and ''' / """ docstrings — without leaving the editor. Inspired by inline-math preview extensions, scoped to comments so your math notation in code reads as math.

What it does

• Hover preview — hover the mouse over a $...$ or $$...$$ span inside a comment and a popup shows the rendered math.
• Cursor preview — move the caret (or make a selection) into a math span and a rendered image appears inline, just after the span. Updates live as you move.
• Only text between $...$ (inline) and $$...$$ (display) is rendered, so ordinary prose in a comment is never treated as math.
• Rendering is done by KaTeX, bundled offline — no network access required.

Scope

Math inside ordinary string literals is not rendered (only comments), and a # or $ inside a normal string is correctly ignored.

Install

From the packaged .vsix:

code --install-extension latex-comment-preview-0.1.0.vsix

Or in VS Code: Extensions panel → ⋯ menu → Install from VSIX…

Develop / run from source

npm install
npm run build          # bundle to dist/extension.js
# then press F5 in VS Code to launch an Extension Development Host

Open sample.py in the dev host to try it.

Example

The repo's sample.py demonstrates what does and doesn't render — hover the math, or move the caret onto a math line to reveal the source:

# The overlap matrix element is the inner product $S_{\mu\nu} = \langle \phi_\mu | \phi_\nu \rangle$.

# Display math also works: $$F\mathbf{c} = \epsilon S \mathbf{c}$$

def scf_energy():
    """
    Computes the SCF energy.

    The Fock matrix is $F = h + J - K$ where the exchange term keeps
    same-spin electrons apart. Total energy:

    $$E = \sum_{\mu\nu} P_{\mu\nu} (h_{\mu\nu} + F_{\mu\nu}) / 2$$
    """
    pass

# Plain prose with no math is never rendered, even in a # comment.
# Escaped \$5.00 is not a delimiter.

x = "a string with a # and a $ inside should be ignored"  # but $E=mc^2$ here renders

Note the last line: #/$ inside a normal string literal are ignored — only the $E=mc^2$ in the trailing comment renders.

Settings

Command: LaTeX Comment Preview: Toggle (latexCommentPreview.toggle).

How it works

1. A lightweight line scanner tracks comment / docstring / string state and extracts $...$ and $$...$$ spans with exact document ranges, tagging each span as comment or docstring (src/parser.ts).
2. Each span is rendered by KaTeX to MathML, wrapped in an SVG foreignObject, and embedded as a data: URI so it can appear in both a Markdown hover and an inline decoration (src/render.ts). Results are cached.
3. Inline rendering hides the raw $...$ source and draws the math in its place; the raw source reappears when the caret is on that line so you can edit it.
4. Span color is resolved from the active theme's own comment / string token colors (read from the theme JSON), so the math matches the surrounding code (src/theme.ts).
5. Inline width is measured exactly by a background webview that lays the math out with real KaTeX fonts and reports getBoundingClientRect(), eliminating the trailing gap (src/measurer.ts), gated by useWebviewMeasure. When that setting is off, a font-metric estimate is used instead.

Known limitations

• Inline width is an estimate that may leave a small trailing gap (it never clips). For exact widths, enable useWebviewMeasure — which adds a small "LaTeX Measurer" view to the Explorer sidebar (safe to leave collapsed; it only measures).

License

MIT

Author: Evan S. Robles Contact: GitHub @evan-robles