Replace TEXT_MOB_SCALE_FACTOR with a dynamically calculated value (#2423)

- Set font_size_for_unit_height: 144 in config
- Calculate the relevant scaling factors for Text and Text using a rendered "0" as a reference, ensuring that a font size of 144 (or whatever is set) would give it a height of 1 in manim coordinates.

Author: 3b1b

manimlib/default_config.yml

@@ -82,10 +82,14 @@ mobject:
 tex:
   # See tex_templates.yml
   template: "default"
+  # The font size at which Tex("0") has a height of 1 manim unit
+  font_size_for_unit_height: 144
 text:
   # font: "Cambria Math"
   font: "Consolas"
   alignment: "LEFT"
+  # The font size at which Text("0") has a height of 1 manim unit
+  font_size_for_unit_height: 144
 embed:
   exception_mode: "Verbose"
   autoreload: False

manimlib/mobject/svg/old_tex_mobject.py

@@ -6,6 +6,7 @@
 
 from manimlib.constants import BLACK, DEFAULT_MOBJECT_COLOR
 from manimlib.mobject.svg.svg_mobject import SVGMobject
+from manimlib.mobject.svg.tex_mobject import get_tex_mob_scale_factor
 from manimlib.mobject.types.vectorized_mobject import VGroup
 from manimlib.utils.tex_file_writing import latex_to_svg
 
@@ -16,9 +17,6 @@
     from manimlib.typing import ManimColor
 
 
-SCALE_FACTOR_PER_FONT_POINT = 0.001
-
-
 class SingleStringTex(SVGMobject):
     height: float | None = None
 
@@ -59,7 +57,7 @@ def __init__(
         )
 
         if self.height is None:
-            self.scale(SCALE_FACTOR_PER_FONT_POINT * self.font_size)
+            self.scale(get_tex_mob_scale_factor() * self.font_size)
         if self.organize_left_to_right:
             self.organize_submobjects_left_to_right()
 

manimlib/mobject/svg/svg_mobject.py

@@ -31,6 +31,21 @@
 PATH_TO_POINTS: dict[str, Vect3Array] = {}
 
 
+def get_svg_content_height(svg_string: str) -> float:
+    # Strip root attributes to match SVGMobject.modify_xml_tree,
+    # which avoids viewBox unit conversions (e.g. pt to px for dvisvgm)
+    root = ET.fromstring(svg_string)
+    root.attrib.clear()
+    data_stream = io.BytesIO()
+    ET.ElementTree(root).write(data_stream)
+    data_stream.seek(0)
+    svg = se.SVG.parse(data_stream)
+    bbox = svg.bbox()
+    if bbox is None:
+        raise ValueError("SVG has no content to measure")
+    return bbox[3] - bbox[1]
+
+
 def _convert_point_to_3d(x: float, y: float) -> np.ndarray:
     return np.array([x, y, 0.0])
 

manimlib/mobject/svg/tex_mobject.py

@@ -3,7 +3,11 @@
 import re
 from pathlib import Path
 
+from functools import lru_cache
+
+from manimlib.config import manim_config
 from manimlib.mobject.svg.string_mobject import StringMobject
+from manimlib.mobject.svg.svg_mobject import get_svg_content_height
 from manimlib.mobject.types.vectorized_mobject import VGroup
 from manimlib.mobject.types.vectorized_mobject import VMobject
 from manimlib.utils.color import color_to_hex
@@ -18,7 +22,14 @@
     from manimlib.typing import ManimColor, Span, Selector, Self
 
 
-TEX_MOB_SCALE_FACTOR = 0.001
+@lru_cache(maxsize=1)
+def get_tex_mob_scale_factor() -> float:
+    # Render a reference "0" and calibrate so that font_size_for_unit_height
+    # gives a height of 1 manim unit. Compensates for platform dvisvgm differences.
+    font_size_for_unit_height = manim_config.tex.font_size_for_unit_height
+    svg_string = latex_to_svg("0", show_message_during_execution=False)
+    svg_height = get_svg_content_height(svg_string)
+    return 1.0 / (font_size_for_unit_height * svg_height)
 
 
 class Tex(StringMobject):
@@ -63,7 +74,7 @@ def __init__(
         )
 
         self.set_color_by_tex_to_color_map(self.tex_to_color_map)
-        self.scale(TEX_MOB_SCALE_FACTOR * font_size)
+        self.scale(get_tex_mob_scale_factor() * font_size)
 
         self.font_size = font_size  # Important for this to go after the scale call
 

manimlib/mobject/svg/text_mobject.py

@@ -17,6 +17,7 @@
 from manimlib.constants import NORMAL
 from manimlib.logger import log
 from manimlib.mobject.svg.string_mobject import StringMobject
+from manimlib.mobject.svg.svg_mobject import get_svg_content_height
 from manimlib.utils.cache import cache_on_disk
 from manimlib.utils.color import color_to_hex
 from manimlib.utils.color import int_to_hex
@@ -31,7 +32,6 @@
     from manimlib.typing import ManimColor, Span, Selector
 
 
-TEXT_MOB_SCALE_FACTOR = 0.0076
 DEFAULT_LINE_SPACING_SCALE = 0.6
 # Ensure the canvas is large enough to hold all glyphs.
 DEFAULT_CANVAS_WIDTH = 16384
@@ -100,6 +100,18 @@ def markup_to_svg(
     return result
 
 
+@lru_cache(maxsize=1)
+def get_text_mob_scale_factor() -> float:
+    # Render a reference "0" and calibrate so that font_size_for_unit_height
+    # gives a height of 1 manim unit. Compensates for platform DPI differences.
+    ref_size = 48
+    font_size_for_unit_height = manim_config.text.font_size_for_unit_height
+    pango_size = str(round(ref_size * 1024))
+    svg_string = markup_to_svg(f'<span font_size="{pango_size}">0</span>')
+    svg_height = get_svg_content_height(svg_string)
+    return ref_size / (font_size_for_unit_height * svg_height)
+
+
 class MarkupText(StringMobject):
     # See https://docs.gtk.org/Pango/pango_markup.html
     MARKUP_TAGS = {
@@ -188,7 +200,7 @@ def __init__(
         if self.t2c:
             self.set_color_by_text_to_color_map(self.t2c)
         if height is None:
-            self.scale(TEXT_MOB_SCALE_FACTOR)
+            self.scale(get_text_mob_scale_factor())
 
     def get_svg_string_by_content(self, content: str) -> str:
         self.content = content