Switch the default egui font to Albert Sans

Follows the same approach as #8261: replaces Ubuntu-Light with a
variable font hinted via ttfautohint, updates fallback references,
loosens a couple of tests that hard-coded font-specific pixel values,
and regenerates all visual snapshots.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/epaint/src/image.rs

@@ -362,7 +362,7 @@ impl core::fmt::Debug for ColorImage {
 /// (which would require more atlas space, but would allow for more accurate rendering of colored text and emojis),
 /// or do the color compensation in the shader, based on the active text color.
 ///
-/// When experimenting, use <https://fonts.google.com/specimen/Ubuntu> to compare to a ground truth.
+/// When experimenting, use <https://fonts.google.com/specimen/Albert+Sans> to compare to a ground truth.
 ///
 /// See <https://hikogui.org/2022/10/24/the-trouble-with-anti-aliasing.html> for related analysis.
 #[derive(Clone, Copy, Debug, Default, PartialEq)]

crates/epaint/src/text/font.rs

@@ -452,10 +452,7 @@ impl FontFace {
         matches!(
             chr,
             // Strip out a religious symbol with secondary nefarious interpretation:
-            '\u{534d}' | '\u{5350}' |
-
-            // Ignore ubuntu-specific stuff in `Ubuntu-Light.ttf`:
-            '\u{E0FF}' | '\u{EFFD}' | '\u{F0FF}' | '\u{F200}'
+            '\u{534d}' | '\u{5350}'
         )
     }
 

crates/epaint/src/text/fonts.rs

@@ -11,7 +11,7 @@ use crate::{
 use emath::{NumExt as _, OrderedFloat, Rangef};
 
 #[cfg(feature = "default_fonts")]
-use epaint_default_fonts::{EMOJI_ICON, HACK_REGULAR, NOTO_EMOJI_REGULAR, UBUNTU_LIGHT};
+use epaint_default_fonts::{ALBERT_SANS, EMOJI_ICON, HACK_REGULAR, NOTO_EMOJI_REGULAR};
 
 // ----------------------------------------------------------------------------
 
@@ -411,7 +411,7 @@ fn blob_from_font_data(data: &FontData) -> Blob {
 /// fonts.font_data.insert("my_font".to_owned(),
 ///    std::sync::Arc::new(
 ///        // .ttf and .otf supported
-///        FontData::from_static(include_bytes!("../../../epaint_default_fonts/fonts/Ubuntu-Light.ttf"))
+///        FontData::from_static(include_bytes!("../../../epaint_default_fonts/fonts/AlbertSans-VariableFont_wght.ttf"))
 ///    )
 /// );
 ///
@@ -518,8 +518,13 @@ impl Default for FontDefinitions {
         );
 
         font_data.insert(
-            "Ubuntu-Light".to_owned(),
-            Arc::new(FontData::from_static(UBUNTU_LIGHT)),
+            "Albert Sans".to_owned(),
+            // Albert Sans is a variable font; a slightly-lighter-than-regular weight
+            // looks best for UI text.
+            Arc::new(FontData::from_static(ALBERT_SANS).tweak(FontTweak {
+                coords: VariationCoords::new([(b"wght", 350.0)]),
+                ..Default::default()
+            })),
         );
 
         // Bigger emojis, and more. <http://jslegers.github.io/emoji-icon-font/>:
@@ -535,7 +540,7 @@ impl Default for FontDefinitions {
             FontFamily::Monospace,
             vec![
                 "Hack".to_owned(),
-                "Ubuntu-Light".to_owned(), // fallback for √ etc
+                "Albert Sans".to_owned(), // fallback for √ etc
                 "NotoEmoji-Regular".to_owned(),
                 "emoji-icon-font".to_owned(),
             ],
@@ -543,7 +548,7 @@ impl Default for FontDefinitions {
         families.insert(
             FontFamily::Proportional,
             vec![
-                "Ubuntu-Light".to_owned(),
+                "Albert Sans".to_owned(),
                 "NotoEmoji-Regular".to_owned(),
                 "emoji-icon-font".to_owned(),
             ],
@@ -573,7 +578,7 @@ impl FontDefinitions {
     #[cfg(feature = "default_fonts")]
     pub fn builtin_font_names() -> &'static [&'static str] {
         &[
-            "Ubuntu-Light",
+            "Albert Sans",
             "NotoEmoji-Regular",
             "emoji-icon-font",
             "Hack",

crates/epaint/src/text/text_layout.rs

@@ -1905,10 +1905,15 @@ mod tests {
             );
 
             // Round-trip: position → cursor → position should be stable.
+            //
+            // A continuation glyph mid-cluster is placed at the pixel-rounded
+            // cursor position, which can differ from the analytic (unrounded)
+            // position by up to one physical pixel depending on the font's
+            // glyph advance widths, so allow a one-pixel slack here.
             let cursor2 = galley.cursor_from_pos(Vec2::new(rect.center().x, rect.center().y));
             let rect2 = galley.pos_from_cursor(cursor2);
             assert!(
-                (rect.min.x - rect2.min.x).abs() < 1.0,
+                (rect.min.x - rect2.min.x).abs() <= 1.0,
                 "Cursor round-trip unstable at index {i}: \
                  first={}, second={}, cursor2.index={}",
                 rect.min.x,