A new option undercurl_style to control the rendering of undercurls

Fixes #5883

docs/changelog.rst

@@ -63,6 +63,8 @@ Detailed list of changes
 
 - Add an option :opt:`background_tint_gaps` to control background image tinting for window gaps (:iss:`5596`)
 
+- A new option :opt:`undercurl_style` to control the rendering of undercurls (:pull:`5883`)
+
 - Bash integration: Fix ``clone-in-kitty`` not working on bash >= 5.2 if an environment variable values contain newlines or other special characters (:iss:`5629`)
 
 - A new :ac:`sleep` action useful in combine based mappings to make kitty sleep before executing the next action

kitty/fonts/render.py

@@ -13,6 +13,7 @@ from kitty.fast_data_types import (
     Screen,
     create_test_font_group,
     get_fallback_font,
+    get_options,
     set_font_data,
     set_options,
     set_send_sprite_to_gpu,
@@ -249,16 +250,15 @@ def add_dline(buf: CBufType, cell_width: int, position: int, thickness: int, cel
 
 def add_curl(buf: CBufType, cell_width: int, position: int, thickness: int, cell_height: int) -> None:
     max_x, max_y = cell_width - 1, cell_height - 1
-    xfactor = 2.0 * pi / max_x
+    opts = get_options()
-    thickness = max(1, thickness)
+    xfactor = (4.0 if 'dense' in opts.undercurl_style else 2.0) * pi / max_x
-    if thickness < 3:
+
-        half_height = thickness
+    max_height = cell_height - (position - thickness // 2)  # descender from the font
-        thickness -= 1
+    half_height = max(1, max_height // 4)
-    elif thickness == 3:
+    if 'thick' in opts.undercurl_style:
-        half_height = thickness = 2
+        thickness = max(half_height, thickness)
     else:
-        half_height = thickness // 2
+        thickness = max(1, thickness) - (1 if thickness < 3 else 2)
-        thickness -= 2
 
     def add_intensity(x: int, y: int, val: int) -> None:
         y += position

kitty/options/definition.py

@@ -220,6 +220,16 @@ The sizes of the lines used for the box drawing Unicode characters. These values
 are in pts. They will be scaled by the monitor DPI to arrive at a pixel value.
 There must be four values corresponding to thin, normal, thick, and very thick
 lines.
+'''
+    )
+
+opt('undercurl_style', 'thin-sparse',
+    choices=('thin-sparse', 'thin-dense', 'thick-sparse', 'thick-dense'),
+    long_text='''
+The style with which undercurls are rendered. This option takes the form
+:code:`(thin|thick)-(sparse|dense)`. Thin and thick control the thickness of the
+undercurl. Sparse and dense control how often the curl oscillates. With sparse
+the curl will peak once per character, with dense twice.
 '''
     )
 egr()  # }}}

kitty/options/parse.py

@@ -1281,6 +1281,14 @@ class Parser:
     def touch_scroll_multiplier(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         ans['touch_scroll_multiplier'] = float(val)
 
+    def undercurl_style(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
+        val = val.lower()
+        if val not in self.choices_for_undercurl_style:
+            raise ValueError(f"The value {val} is not a valid choice for undercurl_style")
+        ans["undercurl_style"] = val
+
+    choices_for_undercurl_style = frozenset(('thin-sparse', 'thin-dense', 'thick-sparse', 'thick-dense'))
+
     def update_check_interval(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         ans['update_check_interval'] = float(val)
 

kitty/options/types.py

@@ -29,6 +29,7 @@ if typing.TYPE_CHECKING:
     choices_for_tab_bar_style = typing.Literal['fade', 'hidden', 'powerline', 'separator', 'slant', 'custom']
     choices_for_tab_powerline_style = typing.Literal['angled', 'round', 'slanted']
     choices_for_tab_switch_strategy = typing.Literal['last', 'left', 'previous', 'right']
+    choices_for_undercurl_style = typing.Literal['thin-sparse', 'thin-dense', 'thick-sparse', 'thick-dense']
     choices_for_window_logo_position = typing.Literal['top-left', 'top', 'top-right', 'left', 'center', 'right', 'bottom-left', 'bottom', 'bottom-right']
 else:
     choices_for_allow_cloning = str
@@ -46,6 +47,7 @@ else:
     choices_for_tab_bar_style = str
     choices_for_tab_powerline_style = str
     choices_for_tab_switch_strategy = str
+    choices_for_undercurl_style = str
     choices_for_window_logo_position = str
 
 option_names = (  # {{{
@@ -442,6 +444,7 @@ option_names = (  # {{{
  'tab_title_template',
  'term',
  'touch_scroll_multiplier',
+ 'undercurl_style',
  'update_check_interval',
  'url_color',
  'url_excluded_characters',
@@ -592,6 +595,7 @@ class Options:
     tab_title_template: str = '{fmt.fg.red}{bell_symbol}{activity_symbol}{fmt.fg.tab}{title}'
     term: str = 'xterm-kitty'
     touch_scroll_multiplier: float = 1.0
+    undercurl_style: choices_for_undercurl_style = 'thin-sparse'
     update_check_interval: float = 24.0
     url_color: Color = Color(0, 135, 189)
     url_excluded_characters: str = ''