Line drawing characters are not smooth

[mgeisler]

I noticed that line drawing characters, like the ones shown all over in CLIs for various LLMs are not rendered the same in Ghostel/Emacs as in a Gnome Terminal.

Ghostel:

Gnome Terminal:

Both are configured to use Victor Mono.

I have not tried with other fonts yet — the main point is that Gnome Terminal seems to do something custom for the line drawing characters to produce a pixel-perfect smooth line. The characters seem to overlap by 1 px or so, or perhaps I'm seeing an anti-aliasing artifact.

I should add that I see the same artifacts in a regular Emacs buffer showing the little demo script:

This makes me think that the issue isn't strictly in Ghostel.

[dakra]

I use a patched version of 'FiraCode Nerd Font' and my lines look good in Emacs.
I assume you have the same problem in org-tables and everywhere else too?
Maybe changing or patching the font helps?
Anyway, I don't think we can do too much about that in ghostel.

Summoning @emil-e as the font/glyph guy ;)

I also gave your issue to Claude so I just dump this answer here as it's maybe helpful:

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Root cause. Modern terminals like Gnome Terminal, ghostty, kitty, iTerm2, Alacritty and wezterm don't actually use the font's box-drawing glyphs. They programmatically rasterize U+2500–U+259F themselves so the segments connect pixel-perfect regardless of font. That happens in the GPU renderer.

Ghostel renders into an Emacs buffer. Emacs gets the glyphs from the font via CoreText/HarfBuzz and there's no hook to override per-codepoint rasterization from a package. So whatever Victor Mono produces is what shows up — same as in any other Emacs buffer, which is exactly what you observed.

Workaround. Redirect the box-drawing block to a font with seamless lines:

(set-fontset-font t '(#x2500 . #x259F) "JetBrains Mono")

JetBrains Mono, Cascadia Code, Iosevka, Berkeley Mono, Fira Code all have well-aligned box-drawing characters. This is global to Emacs, not Ghostel-specific.

[emil-e]

Root cause. Modern terminals like Gnome Terminal, ghostty, kitty, iTerm2, Alacritty and wezterm don't actually use the font's box-drawing glyphs. They programmatically rasterize U+2500–U+259F themselves so the segments connect pixel-perfect regardless of font. That happens in the GPU renderer.

Interesting. I have no idea if this is actually true, but if it is, it might explain things. I'm not sure how feasible it would be for us to do our own line drawing (overriding the font) but we might at least be able to have some special handling for line drawing characters in terms of scaling.

It's always going to be a little tricky to get full parity when it comes to rendering since Emacs renders things in a fundamentally different way compared to an actual terminal - we cannot truly force things into a grid. We can do our best, however.