modify_font strikethrough_position isn't respected on macOS

[fenetikm]

Describe the bug
The modify_font strikethrough_position config option isn't respected - it's just hardcoded.

To Reproduce
Steps to reproduce the behavior:
(on macOS)
1.Set modify_font strikethrough_position 3
2. Have a look at the strikethrough position using, say, echo -e "\e[9mstrikethrough\e[0m"
3. Set modify_font strikethrough_position -3
4. Have a look at the strikethrough position, it will be the same as step 2

Environment details

aths:
  kitty: /Applications/kitty.app/Contents/MacOS/kitty
  base dir: /Applications/kitty.app/Contents/Resources/kitty
  extensions dir: /Applications/kitty.app/Contents/Resources/Python/lib/kitty-extensions
  system shell: /bin/zsh
Loaded config files:
  /Users/michael/.config/kitty/kitty.conf

Config options different from defaults:
bold_font                    Fira Code SemiBold
bold_italic_font             Hack Bold Italic
box_drawing_scale            (0.1, 1.0, 1.5, 2.0)
copy_on_select               clipboard
detect_urls                  False
enable_audio_bell            False
font_family                  Fira Code Regular
font_features:
{'FiraCode-Regular': ('+ss01', '+ss03', '+ss04', '+ss02', '+ss10'),
 'FiraCode-Retina': ('+ss01', '+ss03', '+ss04', '+ss02', '+ss10'),
 'FiraCode-SemiBold': ('+ss01', '+ss03', '+ss04', '+ss02', '+ss10')}
font_size                    15.0
hide_window_decorations      2
input_delay                  2
italic_font                  Hack Italic
macos_option_as_alt          3
macos_thicken_font           0.4
macos_traditional_fullscreen True
modify_font:
    baseline 2
    cell_height -2
    cell_width -1
    strikethrough_position -7
    strikethrough_thickness 200%
    underline_position 1
    underline_thickness 200%
mouse_hide_wait              3.0
remember_window_size         False
single_window_margin_width   FloatEdges(left=2.0, top=2.0, right=2.0, bottom=2.0)
symbol_map:
        U+23fb - U+23fe → Symbols Nerd Font
        U+2665 - U+2665 → Symbols Nerd Font
        U+26a1 - U+26a1 → Symbols Nerd Font
        U+2b58 - U+2b58 → Symbols Nerd Font
        U+e000 - U+e00a → Symbols Nerd Font
        U+e0a0 - U+e0a3 → Symbols Nerd Font
        U+e0b0 - U+e0c8 → Symbols Nerd Font
        U+e0ca - U+e0ca → Symbols Nerd Font
        U+e0cc - U+e0d2 → Symbols Nerd Font
        U+e0d4 - U+e0d4 → Symbols Nerd Font
        U+e200 - U+e2a9 → Symbols Nerd Font
        U+e300 - U+e3e3 → Symbols Nerd Font

... I can see in core_text.m it's just hardcoded as compared with freetype.c. (I also note that strikethrough_thickness just comes from the underline thickness and can't be independently set, again in comparison to the freetype implementation - let me know if you want a separate ticket for that)

Thanks.

[kovidgoyal]

The code to adjust these is backend independent so I dont see how it
could not work of macoS alone. Try using a larger value like say 20%.

[fenetikm]

Here it is with 20%:

50%:

-50%:

Is there something else I could try?

[kovidgoyal]

The code for modifying the positions is all in fonts.c see the calc_cell_metrics() it has nothing platform specific in it.

[fenetikm]

Hmmm doesn't it call cell_metrics to set the initial values which get adjusted? And cell_metrics has a free type version and a coretext version? (I'm not familiar with any of this, just poking around)

freetype.c has this fragment of code in cell_metrics:

    if (self->strikethrough_position != 0) {
      *strikethrough_position = MIN(*cell_height - 1, (unsigned int)font_units_to_pixels_y(self, MAX(0, self->ascender - self->strikethrough_position)));
    } else {
      *strikethrough_position = (unsigned int)floor(*baseline * 0.65);
    }
    if (self->strikethrough_thickness > 0) {
      *strikethrough_thickness = MAX(1, font_units_to_pixels_y(self, self->strikethrough_thickness));
    } else {
      *strikethrough_thickness = *underline_thickness;
    }

and core_text.m just has:

    *strikethrough_position = (unsigned int)floor(*baseline * 0.65);

and:

    *strikethrough_thickness = *underline_thickness;

[kovidgoyal]

Yes, that sets the initial position, which comes from the font file. The
adjustment is applied after.

[fenetikm]

ok thanks - I'll see if I can find the actual issue then.

[fenetikm]

Hi @kovidgoyal - I believe it's the strikethrough_position line in fonts.c:

    if (baseline_before != baseline) {
        int adjustment = baseline - baseline_before;
        baseline = adjust_ypos(baseline_before, cell_height, adjustment);
        underline_position = adjust_ypos(underline_position, cell_height, adjustment);
        strikethrough_position = adjust_ypos(underline_position, cell_height, adjustment);
    }

instead it should be:

        strikethrough_position = adjust_ypos(strikethrough_position, cell_height, adjustment);

I was incorrect re strikethrough thickness, that's working ok.

[fenetikm]

Great, thanks 👍