Feedback: Zoom issues, browser configuration, and Rust dependency on NixOS

[kodonaut]

Hi, I came here from toppair/peek.nvim#93.

I decided to give this plugin a try because I was frustrated by the inability to zoom Mermaid diagrams in other tools. However, my experience so far has been significantly worse than with peek.nvim.

1. Zoom Functionality is Broken

The diagram renders correctly, but zooming is practically unusable:

• Default View: No zoom functionality available.
• Fullscreen Mode: Zoom control buttons appear, but:
  • Zoom Out: Works.
  • Zoom In (+): Does not scale the diagram. It only shifts the entire diagram view downwards while keeping the original size.
• Comparison with Peek: In peek.nvim, at least the entire page scales by browser. Here, it seems like only the header scales, while the diagram canvas remains static.

Tested Browsers: Librewolf and Chromium.

2. Browser Configuration

There is no documentation (or apparent feature) to configure opening the preview in a browser other than the system default. This would be a nice-to-have feature.

3. Rust Renderer & NixOS Compatibility

I noticed the option to switch the renderer to Rust. However, it requires manually installing a Cargo package.

• NixOS Issue: As a NixOS user, I avoid manual imperative installations like this. It breaks the declarative model.
• Personal Preference: I also have a personal aversion to Rust dependencies, but that’s secondary to the NixOS compatibility issue.

Conclusion

I will keep watching the project, so please consider this as constructive feedback. Unfortunately, without proper zoom functionality, I have to return to peek.nvim, even though its zoom capabilities are also somewhat limited.

Thanks for your work!

[kodonaut]

OK, additional feedback...

I decided to give the Rust renderer a try after all, just to see if it would improve things. It didn’t. Zooming still just shifts the entire diagram down.

Moreover, the Rust renderer displays the diagram incorrectly. I’ve attached a screenshot so you can see the issue: it’s a Class Diagram, and you can clearly see overlapping elements in the bottom-left corner.

[selimacerbas]

Hey @kodonaut, thanks for the detailed feedback — it was actually super helpful. Some responses:

1. Zoom in fullscreen — fixed in v1.6.0

You were right, this was a real bug. The overlay container used flex centering with overflow: auto, which meant when the SVG grew wider than the container, the centered overflow pushed content into negative scroll space that scrollbars couldn'''t reach. Looked like nothing was happening when you clicked zoom in, even though the SVG was scaling.

Fixed by adding an inner wrapper div: outer container handles scrolling, inner wrapper handles centering with width: max-content. Standard pattern for scrollable centered content.

Please update to v1.6.0 and try again — should now scale properly in both directions.

2. Browser configuration

Fair request. There'''s an open PR (#13) that adds related improvements, but it bundles unrelated changes. Once that'''s split, I'''ll add a clean browser config option in a follow-up. In the meantime, the only reliable workaround is to change your system default browser:

• Linux: set the BROWSER env var (xdg-open respects it as a colon-separated list)
• macOS: change default browser in System Settings → Desktop & Dock → Default web browser (the open command does NOT respect BROWSER env var — it uses LaunchServices)
• WSL: change the Windows default browser (explorer.exe opens whatever Windows is set to)

3. Default view zoom

The inline preview is intentionally simple — it shows your markdown rendered. Click the expand icon on a mermaid diagram to get the full zoom/pan experience. Adding zoom controls inline would clutter the prose view, but I could consider an "always-on" mode if there'''s demand.

4. Rust renderer + NixOS

Understandable — cargo install is imperative and breaks the declarative model. Unfortunately the Rust renderer is a separate project (mermaid-rs-renderer) maintained by someone else, so I can'''t ship a Nix derivation from here. Worth opening an issue with them — a mermaid-rs-renderer package in nixpkgs would be the right fix. The plugin works fine without it (JS rendering is the default).

5. Rust renderer rendering issues (class diagram overlap)

That'''s a bug in mmdr itself, not the plugin. We just pipe the diagram source to the CLI and embed its SVG output. Worth filing it on the mermaid-rs-renderer repo with the screenshot.

Hope this helps!

[selimacerbas]

Quick follow-up @kodonaut — the browser config option is shipped in v1.7.0.

require("markdown_preview").setup({
  browser = "Firefox",                          -- by app/binary name
  -- or
  browser = "librewolf",                        -- Linux binary
  -- or
  browser = { "google-chrome", "--incognito" }, -- full command with args
})

On macOS, string values use open -a <name> so common app names like "Firefox" or "Google Chrome" work without needing the full path. On Linux/WSL/Windows, the string is invoked directly.

This addresses #2 from your feedback. The remaining items (#3 inline zoom, #4-5 mmdr) are tracked but require either feature decisions or upstream fixes.

[selimacerbas]

Closing this out. Quick recap:

1. Zoom in fullscreen, fixed in v1.6.0
2. Browser configuration, shipped as browser config in v1.7.0
3. Inline diagram zoom, staying as "click expand for the full zoom/pan overlay" for now (keeps the prose view uncluttered). Reopen or file a new issue if there's demand.
4. Rust renderer on NixOS, upstream concern. The right place is mermaid-rs-renderer. Plugin works fine without it.
5. Rust renderer class-diagram rendering bug, also upstream. Please file on mermaid-rs-renderer with your screenshot if you haven't.

Thanks again for the detailed feedback, items 1 and 2 were both very useful.