Terminal ligatures have limited length even when the font supports longer ligatures

[dragoncoder047]

(this appears to be a bug with the new "enable ligatures in terminal" thing that is marked "preview" in settings)

Does this issue occur when all extensions are disabled?: Yes

I am using Fira Code for both the terminal and the editor, which supports "infinite ligatures", one of which is joining multiple #####################'s into one continuous mark by connecting the horizontal strokes.

This works perfectly fine in the editor windows. However when I turn on the ligatures in the terminal, it only works for about ~32 characters before the ligaturized characters vanish.

With ligatures enabled:

With ligatures disabled:

(these are homebrew install command output btw)

system info

CPUs		Apple M3 (8 x 2400)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: enabled_on direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	2, 2, 2
Memory (System)	16.00GB (0.70GB free)
Process Argv	--crash-reporter-id 3690f944-688a-4ee0-964a-0b264992b30f
Screen Reader	no
VM		0%

this is probably a problem with xterm.js but on the chance that it's with vs code's implementation of ligatures I figured I'd report it here first and let the vs code maintainers decide whether it needs to be reported upstream.

sorry for not using the built-in issue reporter but it won't let me embed an image in the body text 🤷 that is a separate problem

[Tyriar]

Nice find 👍

It is indeed a problem in xterm.js, likely it's just hitting some max width for the canvas we render to.

[Tyriar]

Upstream: xtermjs/xterm.js#5246

[Tyriar]

The upstream change will support glyphs up to the width of the maximum supported texture size. You could still hit this limit on very wide screens but this should handle most cases now. A better fix would need a decent amount of refactoring. See xtermjs/xterm.js#5278

[TylerLeonhardt]

These are # signs with Fira Code but at a certain point, they turn all of the # into kind of a ||

Screen.Recording.2025-01-29.at.4.17.03.PM.mov

Also at a certain point they just stop rendering still. This is on a 16in MacBook Pro so it's not like... an unreasonably wide monitor IMO

Below is a series of = signs... even though they look like quotes.

[Tyriar]

I don't know what's happening with the equals that look like quotes, but the long length case is because we now support up to the maximum texture size reported by webgpu. The better approach is to split out the ligature glyphs into their cell sizes, so we can support an unlimited number of them. I didn't do this as it would need a much bigger change. Will keep this open to track that.