From ab13f253bdad5b81662563d4e99c951ec3dbc411 Mon Sep 17 00:00:00 2001
From: lucasmerlin <hi@lucasmerlin.me>
Date: Tue, 23 Sep 2025 16:06:07 +0200
Subject: [PATCH 1/2] Return 0.0 if font not found in glyph_width

---
 crates/epaint/src/text/font.rs  | 15 +++++++++------
 crates/epaint/src/text/fonts.rs | 11 +++++++++++
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/crates/epaint/src/text/font.rs b/crates/epaint/src/text/font.rs
index c452eb4bcb6..063ff1e3403 100644
--- a/crates/epaint/src/text/font.rs
+++ b/crates/epaint/src/text/font.rs
@@ -478,12 +478,15 @@ impl Font<'_> {
     /// Width of this character in points.
     pub fn glyph_width(&mut self, c: char, font_size: f32) -> f32 {
         let (key, glyph_info) = self.glyph_info(c);
-        let font = &self
-            .fonts_by_id
-            .get(&key)
-            .expect("Nonexistent font ID")
-            .ab_glyph_font;
-        glyph_info.advance_width_unscaled.0 * font.px_scale_factor(font_size)
+        if let Some(font) = &self.fonts_by_id.get(&key) {
+            glyph_info.advance_width_unscaled.0 * font.ab_glyph_font.px_scale_factor(font_size)
+        } else {
+            debug_assert_eq!(
+                glyph_info.advance_width_unscaled.0, 0.0,
+                "We had no font, so this should be the zero-width fallback glyph"
+            );
+            0.0
+        }
     }
 
     /// Can we display this glyph?
diff --git a/crates/epaint/src/text/fonts.rs b/crates/epaint/src/text/fonts.rs
index a78242fd41f..3efcbe8ea47 100644
--- a/crates/epaint/src/text/fonts.rs
+++ b/crates/epaint/src/text/fonts.rs
@@ -651,6 +651,8 @@ impl FontsView<'_> {
     }
 
     /// Width of this character in points.
+    ///
+    /// If the font doesn't exist, this will return `0.0`.
     pub fn glyph_width(&mut self, font_id: &FontId, c: char) -> f32 {
         self.fonts
             .font(&font_id.family)
@@ -1302,4 +1304,13 @@ mod tests {
             }
         }
     }
+
+    #[test]
+    fn test_fallback_glyph_width() {
+        let mut fonts = Fonts::new(1024, AlphaFromCoverage::default(), FontDefinitions::empty());
+        let mut view = fonts.with_pixels_per_point(1.0);
+
+        let width = view.glyph_width(&FontId::new(12.0, FontFamily::Proportional), ' ');
+        assert_eq!(width, 0.0);
+    }
 }

From ea53e8c3264f5566dd0bf0866c3904e68acbc75b Mon Sep 17 00:00:00 2001
From: lucasmerlin <hi@lucasmerlin.me>
Date: Tue, 30 Sep 2025 09:50:37 +0200
Subject: [PATCH 2/2] Remove debug assert

---
 crates/epaint/src/text/font.rs | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/crates/epaint/src/text/font.rs b/crates/epaint/src/text/font.rs
index 063ff1e3403..82fd1aab052 100644
--- a/crates/epaint/src/text/font.rs
+++ b/crates/epaint/src/text/font.rs
@@ -481,10 +481,6 @@ impl Font<'_> {
         if let Some(font) = &self.fonts_by_id.get(&key) {
             glyph_info.advance_width_unscaled.0 * font.ab_glyph_font.px_scale_factor(font_size)
         } else {
-            debug_assert_eq!(
-                glyph_info.advance_width_unscaled.0, 0.0,
-                "We had no font, so this should be the zero-width fallback glyph"
-            );
             0.0
         }
     }