Use height to determine font_size instead of the _font_size attribute. (#1985)

* fix set_value and add some docs

* improve font_size property for tex/text_mobject.py

* add tests

* add more font_size tests

* round test_set_value_size)

* scale based on self._font_size

* add changing_font_size test

* rewrite test and add test i forgot to add

* improve hacky solution that didn't work

* add change font_size test for tex_mobject.py

* improve tests

* split into separate test

* remove component of old test

* fix docs

* simplify the setter

Author: hydrobeam

manim/mobject/numbers.py

@@ -99,7 +99,7 @@ def __init__(
     @property
     def font_size(self):
         """The font size of the tex mobject."""
-        return self._font_size
+        return self.height / self.initial_height * self._font_size
 
     @font_size.setter
     def font_size(self, font_val):
@@ -111,8 +111,7 @@ def font_size(self, font_val):
 
             # scale to a factor of the initial height so that setting
             # font_size does not depend on current size.
-            self.scale(1 / 48 * font_val * self.initial_height / self.height)
-            self._font_size = font_val
+            self.scale(font_val / self.font_size)
 
     def set_submobjects_from_number(self, number):
         self.number = number
@@ -146,12 +145,12 @@ def set_submobjects_from_number(self, number):
         if self.unit and self.unit.startswith("^"):
             self.unit_sign.align_to(self, UP)
 
-        if self.include_background_rectangle:
-            self.add_background_rectangle()
-
         # track the initial height to enable scaling via font_size
         self.initial_height = self.height
 
+        if self.include_background_rectangle:
+            self.add_background_rectangle()
+
     def get_num_string(self, number):
         if isinstance(number, complex):
             formatter = self.get_complex_formatter()
@@ -217,11 +216,28 @@ def get_complex_formatter(self):
             ]
         )
 
-    def set_value(self, number):
+    def set_value(self, number: float):
+        """Set the value of the :class:`~.DecimalNumber` to a new number.
+
+        Parameters
+        ----------
+        number
+            The value that will overwrite the current number of the :class:`~.DecimalNumber`.
+
+        """
+        # creates a new number mob via `set_submobjects_from_number`
+        # then matches the properties (color, font_size, etc...)
+        # of the previous mobject to the new one
+
+        # old_family needed with cairo
         old_family = self.get_family()
+
+        old_font_size = self.font_size
         move_to_point = self.get_edge_center(self.edge_to_fix)
         old_submobjects = self.submobjects
+
         self.set_submobjects_from_number(number)
+        self.font_size = old_font_size
         self.move_to(move_to_point, self.edge_to_fix)
         for sm1, sm2 in zip(self.submobjects, old_submobjects):
             sm1.match_style(sm2)
@@ -236,11 +252,6 @@ def set_value(self, number):
 
         return self
 
-    def scale(self, scale_factor, **kwargs):
-        super().scale(scale_factor, **kwargs)
-        self._font_size *= scale_factor
-        return self
-
     def get_value(self):
         return self.number
 

manim/mobject/svg/tex_mobject.py

@@ -121,7 +121,7 @@ def __repr__(self):
     @property
     def font_size(self):
         """The font size of the tex mobject."""
-        return self._font_size
+        return self.height / self.initial_height / SCALE_FACTOR_PER_FONT_POINT
 
     @font_size.setter
     def font_size(self, font_val):
@@ -133,13 +133,7 @@ def font_size(self, font_val):
 
             # scale to a factor of the initial height so that setting
             # font_size does not depend on current size.
-            self.scale(
-                SCALE_FACTOR_PER_FONT_POINT
-                * font_val
-                * self.initial_height
-                / self.height
-            )
-            self._font_size = font_val
+            self.scale(font_val / self.font_size)
 
     def get_modified_expression(self, tex_string):
         result = tex_string

manim/mobject/svg/text_mobject.py

@@ -535,21 +535,22 @@ def __repr__(self):
 
     @property
     def font_size(self):
-        return self._font_size
+        return (
+            self.height
+            / self.initial_height
+            / TEXT_MOB_SCALE_FACTOR
+            * 2.4
+            * self._font_size
+            / DEFAULT_FONT_SIZE
+        )
 
     @font_size.setter
     def font_size(self, font_val):
+        # TODO: use pango's font size scaling.
         if font_val <= 0:
             raise ValueError("font_size must be greater than 0.")
         else:
-            # multiply by (1/2.4) because it makes it work.
-            self.scale(
-                TEXT_MOB_SCALE_FACTOR
-                * (1 / 2.4)
-                * font_val
-                * self.initial_height
-                / self.height
-            )
+            self.scale(font_val / self.font_size)
 
     def gen_chars(self):
         chars = self.get_group_class()()
@@ -1153,21 +1154,22 @@ def __init__(
 
     @property
     def font_size(self):
-        return self._font_size
+        return (
+            self.height
+            / self.initial_height
+            / TEXT_MOB_SCALE_FACTOR
+            * 2.4
+            * self._font_size
+            / DEFAULT_FONT_SIZE
+        )
 
     @font_size.setter
     def font_size(self, font_val):
         # TODO: use pango's font size scaling.
         if font_val <= 0:
             raise ValueError("font_size must be greater than 0.")
         else:
-            self.scale(
-                TEXT_MOB_SCALE_FACTOR
-                * (1 / 2.4)
-                * font_val
-                * self.initial_height
-                / self.height
-            )
+            self.scale(font_val / self.font_size)
 
     def text2hash(self):
         """Generates ``sha256`` hash for file name."""

tests/control_data/graphical_units_data/numbers/set_value_with_updaters.npz

@@ -0,0 +1,24 @@
+from manim import *
+from tests.test_graphical_units.testing.frames_comparison import frames_comparison
+
+__module_test__ = "numbers"
+
+
+@frames_comparison(last_frame=False)
+def test_set_value_with_updaters(scene):
+    """Test that the position of the decimal updates properly"""
+    decimal = DecimalNumber(
+        0,
+        show_ellipsis=True,
+        num_decimal_places=3,
+        include_sign=True,
+    )
+    square = Square().to_edge(UP)
+
+    decimal.add_updater(lambda d: d.next_to(square, RIGHT))
+    decimal.add_updater(lambda d: d.set_value(square.get_center()[1]))
+    scene.add(square, decimal)
+    scene.play(
+        square.animate.to_edge(DOWN),
+        rate_func=there_and_back,
+    )

tests/test_graphical_units/test_numbers.py

@@ -0,0 +1,37 @@
+import pytest
+
+from manim.mobject.numbers import DecimalNumber
+
+
+def test_font_size():
+    """Test that DecimalNumber returns the correct font_size value
+    after being scaled."""
+    num = DecimalNumber(0).scale(0.3)
+
+    assert round(num.font_size, 5) == 14.4
+
+
+def test_font_size_vs_scale():
+    """Test that scale produces the same results as .scale()"""
+    num = DecimalNumber(0, font_size=12)
+    num_scale = DecimalNumber(0).scale(1 / 4)
+
+    assert num.height == num_scale.height
+
+
+def test_changing_font_size():
+    """Test that the font_size property properly scales DecimalNumber."""
+    num = DecimalNumber(0, font_size=12)
+    num.font_size = 48
+
+    assert num.height == DecimalNumber(0, font_size=48).height
+
+
+def test_set_value_size():
+    """Test that the size of DecimalNumber after set_value is correct."""
+    num = DecimalNumber(0).scale(0.3)
+    test_num = num.copy()
+    num.set_value(0)
+
+    # round because the height is off by 1e-17
+    assert round(num.height, 12) == round(test_num.height, 12)

tests/test_numbers.py

@@ -81,3 +81,27 @@ def test_tex_size():
     horizontal = text.get_right() - text.get_left()
     assert round(vertical[1], 4) == 0.3512
     assert round(horizontal[0], 4) == 1.0420
+
+
+def test_font_size():
+    """Test that tex_mobject classes return
+    the correct font_size value after being scaled."""
+    string = MathTex(0).scale(0.3)
+
+    assert round(string.font_size, 5) == 14.4
+
+
+def test_font_size_vs_scale():
+    """Test that scale produces the same results as .scale()"""
+    num = MathTex(0, font_size=12)
+    num_scale = MathTex(0).scale(1 / 4)
+
+    assert num.height == num_scale.height
+
+
+def test_changing_font_size():
+    """Test that the font_size property properly scales tex_mobject.py classes."""
+    num = Tex("0", font_size=12)
+    num.font_size = 48
+
+    assert num.height == Tex("0", font_size=48).height

tests/test_texmobject.py

@@ -0,0 +1,13 @@
+import pytest
+
+from manim.mobject.svg.text_mobject import MarkupText, Text
+
+
+def test_font_size():
+    """Test that Text and MarkupText return the
+    correct font_size value after being scaled."""
+    text_string = Text("0").scale(0.3)
+    markuptext_string = MarkupText("0").scale(0.3)
+
+    assert round(text_string.font_size, 5) == 14.4
+    assert round(markuptext_string.font_size, 5) == 14.4