Undercurl support

[bellini666]

Hi,

Trying to set some LSP/Spell highlights to use undercurl instead of underline but it doesn't seem to work with neovim-gtk. For example, with:

highlight! SpellBad guibg=NONE cterm=undercurl gui=undercurl guisp=#ef2929

I get this on terminal (using gnome-terminal btw):

And this on neovim-gtk:

Even the color seems wrong in that example

[Lyude]

I think there might be more that's required to trigger this, on the latest git main undercurl appears to work fine for me:

I tried some of the highlighting categories with my local LSP setup + rust as well just to make sure:

What font are you using? On that note, I wonder if it might be good to just get the rest of your .vimrc

[jacobmischka]

I admit I'm not yet using this fork as my daily driver and haven't tested it in a few weeks, but undercurl also worked fine for me last I did.

[bellini666]

Here is my whole neovimrc: https://github.com/bellini666/dotfiles/tree/master/vim

This is the specific function that gets loaded from an autocmd that runs when the GUI itself loads: https://github.com/bellini666/dotfiles/blob/master/vim/lua/options.lua#L153

For font I'm using Inconsolata patched from Nerd Fonts, specifically this one: https://github.com/ryanoasis/nerd-fonts/blob/master/patched-fonts/Inconsolata/complete/Inconsolata%20Nerd%20Font%20Complete.otf?raw=true

Note that I'm using Debian Unstable, which I update daily. I don't know exactly what system libs neovim-gtk interacts with to do things like undercurl work, but if you tell me I can tell you what is the version that I have installed of those libs

[Lyude]

Note that I'm using Debian Unstable, which I update daily. I don't know exactly what system libs neovim-gtk interacts with to do things like undercurl work, but if you tell me I can tell you what is the version that I have installed of those libs

Yeah this would probably also be useful to know just in case

[Lyude]

Note that I'm using Debian Unstable, which I update daily. I don't know exactly what system libs neovim-gtk interacts with to do things like undercurl work, but if you tell me I can tell you what is the version that I have installed of those libs

Yeah this would probably also be useful to know just in case

Whoops I actually forgot to mention the libraries :P. It would be cairo, pango, and gtk+ - but I'm not sure that's causing the problem though because I managed to get neovim-gtk running in a Debian Unstable container in podman and I didn't see any issues there either. Could you try changing your font to something like "Source Code Pro 11" to see if that changes anything? (Also JFYI - haven't had a chance to go through your .vimrc yet)

[bellini666]

Hey @Lyude ,

Testing "Source Code Pro 11" did make the undercurl somewhat "work". But it is rendering it really different than from my terminal:

Terminal using source code pro:

neovim-gtk using source code pro:

Also note that the terminal from my previous example was also using Inconsolata, and my terminal emulator is gnome-terminal.

Btw, here are the relevant libs from my system:

ii  libpango-1.0-0:amd64                  1.48.10+ds1-1
ii  libcairo2:amd64                       1.16.0-5
ii  libgtk-3-0:amd64                      3.24.30-4
ii  libgtk-4-1:amd64                      4.4.1+ds1-3 

Please tell me if you need any more info

[jacobmischka]

That second image is what is to be expected, the undercurl in gnome-shell is different. The kerning or line height of your original font must be causing it to render mostly below the line, cutting it off except for the very top.

[bellini666]

Hey @jacobmischka ,

Just a quick note, it is not actually gnome-shell but gnome-terminal. I mentioned it because, theoretically, both use the same base libs (pangpo/cairo/gtk) for rendering stuff.

Now, related to the issue that you mentioned... What can be done to solve it? The issue happened to that font in specific, but it can in theory happen to others that have the same issue.

Can it be worked around at neovim-gtk's side?

[jacobmischka]

Er sorry, yes, I meant gnome-terminal. Misspoke.

[Lyude]

Hey @jacobmischka ,

Just a quick note, it is not actually gnome-shell but gnome-terminal. I mentioned it because, theoretically, both use the same base libs (pangpo/cairo/gtk) for rendering stuff.

Now, related to the issue that you mentioned... What can be done to solve it? The issue happened to that font in specific, but it can in theory happen to others that have the same issue.

Can it be worked around at neovim-gtk's side?

Potentially - I like to think that if VTE (the underlying terminal library that gnome-terminal uses, which is the one that employs a combination of pango/cairo/gtk in order to provide a terminal emulation widget) can do it, there's also probably a way we can implement it in neovim-gtk.

…However, next time I sit down to fix this issue I think I've already noticed a good hint as to what might be happening here. If you zoom in and look at the line that we draw in @bellini666's screenshot very closely, you'll notice it's not actually a straight line of red pixels with the same color - the color varies as the line goes on, which might mean we are actually drawing the undercurl - but the damage box ("damage" as in the area within the neovim-gtk drawing area that has been modified as a result of the screen changing, and must be redrawn with cairo. neovim-gtk typically calls these "dirty" regions) we're calculating for each glyph is too small and ends up cutting off part of the undercurl. So - I think that's likely going to end up being the actual issue that needs to be fixed here

[Lyude]

Hey @Lyude ,

Testing "Source Code Pro 11" did make the undercurl somewhat "work". But it is rendering it really different than from my terminal:

Terminal using source code pro:

neovim-gtk using source code pro:

Also note that the terminal from my previous example was also using Inconsolata, and my terminal emulator is gnome-terminal.

Btw, here are the relevant libs from my system:

ii  libpango-1.0-0:amd64                  1.48.10+ds1-1
ii  libcairo2:amd64                       1.16.0-5
ii  libgtk-3-0:amd64                      3.24.30-4
ii  libgtk-4-1:amd64                      4.4.1+ds1-3 

Please tell me if you need any more info

Also as for this difference - I wonder if VTE is actually using pango for drawing the undercurl or if it's drawing it manually using cairo - which might explain the difference in how the two look

[Lyude]

That second image is what is to be expected, the undercurl in gnome-shell is different. The kerning or line height of your original font must be causing it to render mostly below the line, cutting it off except for the very top.

Also whoops, looks like someone already figured out the damage region issues! Sorry I missed this comment lol

[bellini666]

Hey @Lyude ,

Digging around I saw that this is where vte draws the undercurl, which basically calls this function that draws it directly on cairo. That's why it looks so pretty.

I tried to mess around with the neovim-gtk's drawing code and this basically fixed things for me:

diff --git src/render/mod.rs src/render/mod.rs
index 5649691..5e234f0 100644
--- src/render/mod.rs
+++ src/render/mod.rs
@@ -182,10 +182,9 @@ fn draw_underline_strikethrough(
 
         if cell.hl.undercurl {
             let sp = hl.actual_cell_sp(cell).inverse(inverse_level);
-            ctx.set_source_rgba(sp.0, sp.1, sp.2, 0.7);
+            ctx.set_source_rgb(sp.0, sp.1, sp.2);
 
-            let max_undercurl_height = (line_height - underline_position) * 2.0;
-            let undercurl_height = (underline_thickness * 4.0).min(max_undercurl_height);
+            let undercurl_height = underline_thickness * 4.0;
             let undercurl_y = line_y + underline_position - undercurl_height / 2.0;
 
             pangocairo::functions::show_error_underline(

Also, that rgba also explains why the color was different than what I was setting in neovim.

Here are the results:

Using inconsolata (my font, that was having problems before):

Using source code pro (which was working before to show that it did not break):

Don't know if there could be any drawbacks with that, but if there isn't, applying that diff should fix this issue.

Also, it would be pretty awesome to copy the vte cairo rendering in the future to have its pretty undercurl rendering (but that's for another issue).

[Lyude]

Hey @Lyude ,

Digging around I saw that this is where vte draws the undercurl, which basically calls this function that draws it directly on cairo. That's why it looks so pretty.

I tried to mess around with the neovim-gtk's drawing code and this basically fixed things for me:

diff --git src/render/mod.rs src/render/mod.rs
index 5649691..5e234f0 100644
--- src/render/mod.rs
+++ src/render/mod.rs
@@ -182,10 +182,9 @@ fn draw_underline_strikethrough(
 
         if cell.hl.undercurl {
             let sp = hl.actual_cell_sp(cell).inverse(inverse_level);
-            ctx.set_source_rgba(sp.0, sp.1, sp.2, 0.7);
+            ctx.set_source_rgb(sp.0, sp.1, sp.2);
 
-            let max_undercurl_height = (line_height - underline_position) * 2.0;
-            let undercurl_height = (underline_thickness * 4.0).min(max_undercurl_height);
+            let undercurl_height = underline_thickness * 4.0;
             let undercurl_y = line_y + underline_position - undercurl_height / 2.0;
 
             pangocairo::functions::show_error_underline(

Also, that rgba also explains why the color was different than what I was setting in neovim.

Here are the results:

Using inconsolata (my font, that was having problems before):

Using source code pro (which was working before to show that it did not break):

Don't know if there could be any drawbacks with that, but if there isn't, applying that diff should fix this issue.

Lol. I literally wrote up equivalent code on my branch just now before checking back on this issue to find your patch :P. You were close but not quite (although you were right on the rgba bits) - the whole idea we're using for calculating the height of the undercurl here just turned out to be wrong and we need to use the pango descent instead. I've actually managed to reproduce the issue locally and confirmed this fixes it, so I'm going to push :). Thanks for the help!

Also, it would be pretty awesome to copy the vte cairo rendering in the future to have its pretty undercurl rendering (but that's for another issue).

Yes it would be - feel free to file it as a feature request though! No guarantees when I'd get to it though