Use system fonts instead of embedded fonts (#1429)

Author: TheTripleV

source/_extensions/post_process.py

@@ -14,6 +14,8 @@
     cleanup_fontawesome_font_files,
 )
 
+from .post_process_tasks.systemfonts import switch_to_system_fonts
+
 READTHEDOCS_BUILDERS = ["readthedocs", "readthedocsdirhtml"]
 
 
@@ -31,6 +33,7 @@ def do(app: Sphinx, exception: Union[Exception, None]) -> None:
     # The two fontawesome functions must run in order
     cleanup_fontawesome_css(app)
     cleanup_fontawesome_font_files(app)
+    switch_to_system_fonts(app)
 
 
 def setup(app: Sphinx) -> Dict[str, Any]:

source/_extensions/post_process_tasks/systemfonts.py

@@ -0,0 +1,62 @@
+import inspect
+import math
+import re
+from pathlib import Path
+
+from sphinx.application import Sphinx
+
+
+def switch_to_system_fonts(app: Sphinx) -> None:
+    """
+    Removes custom fonts and replaces their usage with system fonts.
+    This can't be done in frc-rtd.css. frc-rtd.css is loaded in after the
+    rtd theme's css is loaded. The custom fonts seems to start downloading
+    before frc-rtd.css is parsed.
+    """
+
+    _name = inspect.stack()[0][3]
+    print("Running", _name)
+    outdir = Path(app.outdir)
+
+    RE_FONT = re.compile(r"(@font-face\{)|(font-family:.*?(?:;|\}))")
+
+    css_path = outdir / "_static" / "css"
+    theme_css_file = css_path / "theme.css"
+
+    theme_text = theme_css_file.read_text(encoding="utf-8")
+
+    def sub_font_faces(match: re.Match):
+        """
+        Delete font faces we don't want
+        """
+        text = match.group()
+        if "Roboto Slab" in text:
+            return ""
+        if "Lato" in text:
+            return ""
+        return text
+
+    theme_text = re.sub(r"@font-face\{.*?\}", sub_font_faces, theme_text)
+
+    def sub_font_usage(match: re.Match):
+        """
+        Replace custom fonts with system fonts
+        """
+        text, ending = match.groups()
+
+        if "Roboto Slab" in text:
+            text = '-apple-system,BlinkMacSystemFont,"Segoe UI Variable Display", "Segoe UI", Roboto,Tahoma,Helvetica,Arial,sans-serif,"Apple Color Emoji","Segoe UI Emoji", "Segoe UI Symbol";'
+        elif "Lato" in text:
+            text = '-apple-system,BlinkMacSystemFont,"Segoe UI Variable Text", "Segoe UI", Roboto,Tahoma,Helvetica,Arial,sans-serif,"Apple Color Emoji","Segoe UI Emoji", "Segoe UI Symbol";'
+
+        return f"font-family:{text}{ending}"
+
+    theme_text = re.sub(r"font-family:(.*?)(;|\})", sub_font_usage, theme_text)
+
+    theme_css_file.write_text(theme_text, encoding="utf-8")
+
+    for path in css_path.glob("fonts/*"):
+        if path.name.lower().startswith("lato"):
+            path.unlink()
+        if path.name.lower().startswith("roboto"):
+            path.unlink()