Add darker, lighter and contrasting methods to ManimColor (#3992)

* Add darker, lighter and contrasting methods to ManimColor

* Fixes

---------

Co-authored-by: Benjamin Hackl <[email protected]>

Author: hchargois

manim/utils/color/core.py

@@ -585,7 +585,7 @@ def invert(self, with_alpha=False) -> Self:
             new[-1] = alpha
             return self._construct_from_space(new)
 
-    def interpolate(self, other: ManimColor, alpha: float) -> Self:
+    def interpolate(self, other: Self, alpha: float) -> Self:
         """Interpolates between the current and the given ManimColor an returns the interpolated color
 
         Parameters
@@ -606,6 +606,99 @@ def interpolate(self, other: ManimColor, alpha: float) -> Self:
             self._internal_space * (1 - alpha) + other._internal_space * alpha
         )
 
+    def darker(self, blend: float = 0.2) -> Self:
+        """Returns a new color that is darker than the current color, i.e.
+        interpolated with black. The opacity is unchanged.
+
+        Parameters
+        ----------
+        blend : float, optional
+            The blend ratio for the interpolation, from 0 (the current color
+            unchanged) to 1 (pure black). By default 0.2 which results in a
+            slightly darker color
+
+        Returns
+        -------
+        ManimColor
+            The darker ManimColor
+
+        See Also
+        --------
+        :meth:`lighter`
+        """
+        from manim.utils.color.manim_colors import BLACK
+
+        alpha = self._internal_space[3]
+        black = self._from_internal(BLACK._internal_value)
+        return self.interpolate(black, blend).opacity(alpha)
+
+    def lighter(self, blend: float = 0.2) -> Self:
+        """Returns a new color that is lighter than the current color, i.e.
+        interpolated with white. The opacity is unchanged.
+
+        Parameters
+        ----------
+        blend : float, optional
+            The blend ratio for the interpolation, from 0 (the current color
+            unchanged) to 1 (pure white). By default 0.2 which results in a
+            slightly lighter color
+
+        Returns
+        -------
+        ManimColor
+            The lighter ManimColor
+
+        See Also
+        --------
+        :meth:`darker`
+        """
+        from manim.utils.color.manim_colors import WHITE
+
+        alpha = self._internal_space[3]
+        white = self._from_internal(WHITE._internal_value)
+        return self.interpolate(white, blend).opacity(alpha)
+
+    def contrasting(
+        self,
+        threshold: float = 0.5,
+        light: Self | None = None,
+        dark: Self | None = None,
+    ) -> Self:
+        """Returns one of two colors, light or dark (by default white or black),
+        that contrasts with the current color (depending on its luminance).
+        This is typically used to set text in a contrasting color that ensures
+        it is readable against a background of the current color.
+
+        Parameters
+        ----------
+        threshold : float, optional
+            The luminance threshold that dictates whether the current color is
+            considered light or dark (and thus whether to return the dark or
+            light color, respectively), by default 0.5
+        light : ManimColor, optional
+            The light color to return if the current color is considered dark,
+            by default pure white
+        dark : ManimColor, optional
+            The dark color to return if the current color is considered light,
+            by default pure black
+
+        Returns
+        -------
+        ManimColor
+            The contrasting ManimColor
+        """
+        from manim.utils.color.manim_colors import BLACK, WHITE
+
+        luminance, _, _ = colorsys.rgb_to_yiq(*self.to_rgb())
+        if luminance < threshold:
+            if light is not None:
+                return light
+            return self._from_internal(WHITE._internal_value)
+        else:
+            if dark is not None:
+                return dark
+            return self._from_internal(BLACK._internal_value)
+
     def opacity(self, opacity: float) -> Self:
         """Creates a new ManimColor with the given opacity and the same color value as before
 
@@ -1282,7 +1375,7 @@ def color_gradient(
 
 
 def interpolate_color(
-    color1: ManimColorT, color2: ManimColor, alpha: float
+    color1: ManimColorT, color2: ManimColorT, alpha: float
 ) -> ManimColorT:
     """Standalone function to interpolate two ManimColors and get the result refer to :meth:`interpolate` in :class:`ManimColor`
 

manim/utils/color/manim_colors.py

@@ -46,21 +46,22 @@ def subnames(name):
             for line, char in zip(color_groups[0], "abcde"):
                 color_groups.add(Text(char).scale(0.6).next_to(line, LEFT, buff=0.2))
 
-            def named_lines_group(length, colors, names, text_colors, align_to_block):
+            def named_lines_group(length, color_names, labels, align_to_block):
+                colors = [getattr(Colors, color.upper()) for color in color_names]
                 lines = VGroup(
                     *[
                         Line(
                             ORIGIN,
                             RIGHT * length,
                             stroke_width=55,
-                            color=getattr(Colors, color.upper()),
+                            color=color,
                         )
                         for color in colors
                     ]
                 ).arrange_submobjects(buff=0.6, direction=DOWN)
 
-                for line, name, color in zip(lines, names, text_colors):
-                    line.add(Text(name, color=color).scale(0.6).move_to(line))
+                for line, name, color in zip(lines, labels, colors):
+                    line.add(Text(name, color=color.contrasting()).scale(0.6).move_to(line))
                 lines.next_to(color_groups, DOWN, buff=0.5).align_to(
                     color_groups[align_to_block], LEFT
                 )
@@ -79,7 +80,6 @@ def named_lines_group(length, colors, names, text_colors, align_to_block):
                 3.2,
                 other_colors,
                 other_colors,
-                [BLACK] * 4 + [WHITE] * 2,
                 0,
             )
 
@@ -95,7 +95,6 @@ def named_lines_group(length, colors, names, text_colors, align_to_block):
                     "darker_gray / gray_e",
                     "black",
                 ],
-                [BLACK] * 3 + [WHITE] * 4,
                 2,
             )
 
@@ -109,7 +108,6 @@ def named_lines_group(length, colors, names, text_colors, align_to_block):
                 3.2,
                 pure_colors,
                 pure_colors,
-                [BLACK, BLACK, WHITE],
                 6,
             )
 

tests/module/utils/test_manim_color.py

@@ -173,3 +173,32 @@ def test_hsv_init() -> None:
 
 def test_into_HSV() -> None:
     nt.assert_equal(RED.into(HSV).into(ManimColor), RED)
+
+
+def test_contrasting() -> None:
+    nt.assert_equal(BLACK.contrasting(), WHITE)
+    nt.assert_equal(WHITE.contrasting(), BLACK)
+    nt.assert_equal(RED.contrasting(0.1), BLACK)
+    nt.assert_equal(RED.contrasting(0.9), WHITE)
+    nt.assert_equal(BLACK.contrasting(dark=GREEN, light=RED), RED)
+    nt.assert_equal(WHITE.contrasting(dark=GREEN, light=RED), GREEN)
+
+
+def test_lighter() -> None:
+    c = RED.opacity(0.42)
+    cl = c.lighter(0.2)
+    nt.assert_array_equal(
+        cl._internal_value[:3],
+        0.8 * c._internal_value[:3] + 0.2 * WHITE._internal_value[:3],
+    )
+    nt.assert_equal(cl[-1], c[-1])
+
+
+def test_darker() -> None:
+    c = RED.opacity(0.42)
+    cd = c.darker(0.2)
+    nt.assert_array_equal(
+        cd._internal_value[:3],
+        0.8 * c._internal_value[:3] + 0.2 * BLACK._internal_value[:3],
+    )
+    nt.assert_equal(cd[-1], c[-1])