Added :meth:.set_opacity_by_tex method for setting the opacity of parts of Tex mobjects (#3159)

* Added MathTex.set_opacity_by_tex and MathTex.fade_all_but_tex

* Completed unittests for set_opacity_by_tex and fade_all_but_tex

* Added control_data for `fade_all_but_tex` and `set_opacity_by_tex`

* Removed ade_all_but_tex and integrated functionality into set_opacity_by_tex. Included a second parameter 'remaining_opacity' to define the opacity value of the remaining tex

* Added type hints for `set_opacity_by_tex`. Removed type information in docstring. Improved logic of `set_opacity_by_tex` to reduce redundant calls for tex parts

---------

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

Author: MatthewLeeCode

manim/mobject/text/tex_mobject.py

@@ -381,6 +381,29 @@ def set_color_by_tex(self, tex, color, **kwargs):
             part.set_color(color)
         return self
 
+    def set_opacity_by_tex(
+        self, tex: str, opacity: float = 0.5, remaining_opacity: float = None, **kwargs
+    ):
+        """
+        Sets the opacity of the tex specified. If 'remaining_opacity' is specified,
+        then the remaining tex will be set to that opacity.
+
+        Parameters
+        ----------
+        tex
+            The tex to set the opacity of.
+        opacity
+            Default 0.5. The opacity to set the tex to
+        remaining_opacity
+            Default None. The opacity to set the remaining tex to.
+            If None, then the remaining tex will not be changed
+        """
+        if remaining_opacity is not None:
+            self.set_opacity(opacity=remaining_opacity)
+        for part in self.get_parts_by_tex(tex):
+            part.set_opacity(opacity)
+        return self
+
     def set_color_by_tex_to_color_map(self, texs_to_color_map, **kwargs):
         for texs, color in list(texs_to_color_map.items()):
             try:

tests/test_graphical_units/control_data/tex_mobject/set_opacity_by_tex.npz

@@ -18,3 +18,11 @@ def test_color_inheritance(scene):
     VMobject.set_default()
 
     scene.add(vgr)
+
+
+@frames_comparison
+def test_set_opacity_by_tex(scene):
+    """Test that set_opacity_by_tex works correctly."""
+    tex = MathTex("f(x) = y", substrings_to_isolate=["f(x)"])
+    tex.set_opacity_by_tex("f(x)", 0.2, 0.5)
+    scene.add(tex)