From 47c5617740a3e86ccafd9d7008fb3afb6ff7fbf8 Mon Sep 17 00:00:00 2001
From: Lucas Meurer <hi@lucasmerlin.me>
Date: Tue, 30 Sep 2025 10:12:56 +0200
Subject: [PATCH] Return `0.0` if font not found in `glyph_width` instead of
 panic (#7559)

---
 crates/epaint/src/text/font.rs  | 11 +++++------
 crates/epaint/src/text/fonts.rs | 11 +++++++++++
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/crates/epaint/src/text/font.rs b/crates/epaint/src/text/font.rs
index c452eb4b..82fd1aab 100644
--- a/crates/epaint/src/text/font.rs
+++ b/crates/epaint/src/text/font.rs
@@ -478,12 +478,11 @@ 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 {
+            0.0
+        }
     }
 
     /// Can we display this glyph?
diff --git a/crates/epaint/src/text/fonts.rs b/crates/epaint/src/text/fonts.rs
index a78242fd..3efcbe8e 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);
+    }
 }