From 40ba76113ec5a19da9478418fa2eaea24590f3f7 Mon Sep 17 00:00:00 2001
From: Brandon Thomas <echelon@gmail.com>
Date: Mon, 12 Oct 2026 17:35:00 -0400
Subject: [PATCH] Text: a missing font is drawn in Calibri, as PowerPoint does

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
---
 crates/fonts/src/fontdb.rs | 24 ++++++++++++++++++++++++
 crates/fonts/src/lib.rs    | 18 +++++++++++++++++-
 crates/text/src/lib.rs     |  2 +-
 3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/crates/fonts/src/fontdb.rs b/crates/fonts/src/fontdb.rs
index d9c9ece..39b98f3 100644
--- a/crates/fonts/src/fontdb.rs
+++ b/crates/fonts/src/fontdb.rs
@@ -52,6 +52,19 @@ pub fn substitutes(family: &str) -> &'static [&'static str] {
     }
 }
 
+/// Families whose open substitutes ([`substitutes`]) keep their metrics, so text drawn with
+/// them breaks into the same lines.
+fn has_metric_twin(family: &str) -> bool {
+    matches!(
+        family.to_ascii_lowercase().as_str(),
+        "calibri" | "calibri light" | "cambria" | "cambria math" | "arial" | "helvetica" | "times new roman" | "times" | "courier new" | "courier"
+    )
+}
+
+/// The family PowerPoint draws a document's Latin text in when the font it names isn't installed,
+/// whatever the theme, `panose` or `pitchFamily` say.
+pub const MISSING_FONT_FAMILY: &str = "Calibri";
+
 #[derive(Clone)]
 enum FontBytes {
     Static(&'static [u8]),
@@ -756,6 +769,17 @@ impl FontDb {
             .unwrap_or_else(last_resort_face)
     }
 
+    /// The face a document's text in `family` is drawn with, as PowerPoint draws it: the family
+    /// when it is installed or bundled, or a metric-compatible stand-in (Carlito for Calibri,
+    /// Liberation Sans for Arial…); any other missing family is drawn in Calibri (or Carlito).
+    /// DeckCraft's own default family keeps [`FontDb::face`]'s fallbacks.
+    pub fn document_face(&self, family: &str, style: &str) -> Arc<FontFace> {
+        if family.eq_ignore_ascii_case(FALLBACK_FAMILY) || has_metric_twin(family) || self.has_family(family) {
+            return self.face(family, style);
+        }
+        self.face(MISSING_FONT_FAMILY, style)
+    }
+
     fn try_family(&self, family: &str, style: &str) -> Option<Arc<FontFace>> {
         if let Some(f) = self.find(family, style) {
             return Some(f);
diff --git a/crates/fonts/src/lib.rs b/crates/fonts/src/lib.rs
index 8caff94..a83b363 100644
--- a/crates/fonts/src/lib.rs
+++ b/crates/fonts/src/lib.rs
@@ -14,7 +14,9 @@ pub mod script;
 mod shape;
 
 pub use fallback::{bundled_families, covers_cluster, is_emoji_cluster, ligature_carets};
-pub use fontdb::{FALLBACK_FAMILY, FaceRef, FontDb, FontFace, LAST_RESORT_FAMILY, base_style, bundled, substitutes, system_font_dirs};
+pub use fontdb::{
+    FALLBACK_FAMILY, FaceRef, FontDb, FontFace, LAST_RESORT_FAMILY, MISSING_FONT_FAMILY, base_style, bundled, substitutes, system_font_dirs,
+};
 pub use harfrust::Feature;
 use harfrust::Tag;
 pub use kurbo::BezPath;
@@ -182,6 +184,20 @@ mod tests {
         assert!(!shape(&f, "Hello", &[], |c| c).is_empty());
     }
 
+    #[test]
+    fn missing_document_fonts_are_drawn_in_calibri() {
+        // PowerPoint draws a missing family in Calibri, whatever its panose or the theme says.
+        let db = FontDb::global();
+        for missing in ["Qqq Nonexistent", "Avenir Next Qqq", ""] {
+            let f = db.document_face(missing, "Bold");
+            assert_eq!(f.family, db.face(MISSING_FONT_FAMILY, "Bold").family, "{missing:?}");
+        }
+        // Metric-compatible stand-ins and DeckCraft's default keep their own fallbacks.
+        for kept in ["Arial", "Times New Roman", "Cambria", "Courier New", FALLBACK_FAMILY] {
+            assert_eq!(db.document_face(kept, "Regular").family, db.face(kept, "Regular").family, "{kept}");
+        }
+    }
+
     #[test]
     fn office_fonts_have_substitutes() {
         assert!(substitutes("Calibri").contains(&"Carlito"));
diff --git a/crates/text/src/lib.rs b/crates/text/src/lib.rs
index 7144c55..69e6599 100644
--- a/crates/text/src/lib.rs
+++ b/crates/text/src/lib.rs
@@ -261,7 +261,7 @@ fn make_style(ctx: &Ctx, r: &RunProps, scale: f64, prompt: Option<Rgba>) -> Styl
     let family = resolve::font_family(ctx, r);
     let bold = r.bold.unwrap_or(false);
     let italic = r.italic.unwrap_or(false);
-    let face = FontDb::global().face(&family, style_name(bold, italic));
+    let face = FontDb::global().document_face(&family, style_name(bold, italic));
     let fake_bold = bold && face.weight < 550.0;
     let fake_italic = italic && !face.italic;
     let size = (r.size.unwrap_or(18.0) * scale).clamp(0.5, 4000.0);