Convert ANSI dim to RGB

Author: willmcgugan

CHANGELOG.md

@@ -16,6 +16,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Collapsible title now accepts str, Text, or Content https://github.com/Textualize/textual/pull/5697
 - Rich Text objects will be converted to Content in OptionList and other widgets https://github.com/Textualize/textual/pull/5712
+- Textual will always convert dim attributes to RGB by default
+
+### Added
+
+- Added `TEXTUAL_DIM_FACTOR` env var to set the opacity of the 'dim' ANSI attribute
 
 ## [3.0.1] - 2025-04-01
 

src/textual/constants.py

@@ -27,7 +27,9 @@ def _get_environ_bool(name: str) -> bool:
     return has_environ
 
 
-def _get_environ_int(name: str, default: int, minimum: int | None = None) -> int:
+def _get_environ_int(
+    name: str, default: int, minimum: int | None = None, maximum: int | None = None
+) -> int:
     """Retrieves an integer environment variable.
 
     Args:
@@ -48,6 +50,8 @@ def _get_environ_int(name: str, default: int, minimum: int | None = None) -> int
         return default
     if minimum is not None:
         return max(minimum, value)
+    if maximum is not None:
+        return min(maximum, value)
     return value
 
 
@@ -159,5 +163,10 @@ def _get_textual_animations() -> AnimationLevel:
 """
 
 SMOOTH_SCROLL: Final[bool] = _get_environ_int("TEXTUAL_SMOOTH_SCROLL", 1) == 1
-"""Should smooth scrolling be enabled? set `TEXTUAL_SMOOTH_SCROLL=0` to disable smooth
+"""Should smooth scrolling be enabled? set `TEXTUAL_SMOOTH_SCROLL=0` to disable smooth scrolling.
 """
+
+DIM_FACTOR: Final[float] = (
+    _get_environ_int("TEXTUAL_DIM_FACTOR", 50, minimum=0, maximum=100) / 100
+)
+"""Percentage to use as opacity when converting ANSI 'dim' attribute to RGB."""

src/textual/filter.py

@@ -22,6 +22,7 @@
 from rich.terminal_theme import TerminalTheme
 
 from textual.color import Color
+from textual.constants import DIM_FACTOR
 
 
 class LineFilter(ABC):
@@ -125,7 +126,9 @@ def apply(self, segments: list[Segment], background: Color) -> list[Segment]:
 
 
 @lru_cache(1024)
-def dim_color(background: RichColor, color: RichColor, factor: float) -> RichColor:
+def dim_color(
+    background: RichColor, color: RichColor, factor: float = DIM_FACTOR
+) -> RichColor:
     """Dim a color by blending towards the background
 
     Args:
@@ -249,7 +252,7 @@ def truecolor_style(self, style: Style, background: RichColor) -> Style:
             )
         # Convert dim style to RGB
         if style.dim and color is not None:
-            color = dim_color(background, color, 0.5)
+            color = dim_color(background, color)
 
         return Style.from_color(color, bgcolor)