iris: add replaceable glyph atlas buckets

app/src/ui/mod.rs

@@ -550,6 +550,43 @@ mod apply_tests {
         assert!(!rsc.widgets().has_updates());
     }
 
+    #[test]
+    fn replacing_a_font_only_clears_its_glyph_bucket() {
+        let mut rsc = TestRsc {
+            ui: Ui::default(),
+            events: EventManager::default(),
+        };
+        rsc.ui.resize((800.0, 600.0));
+        rsc.ui
+            .register_font_in("first-icons", "first", ICON_FONT)
+            .unwrap();
+        rsc.ui
+            .register_font_in("second-icons", "second", ICON_FONT)
+            .unwrap();
+        let first = wtext(icon::OPEN)
+            .family("first-icons")
+            .add_strong(&mut rsc)
+            .any();
+        let second = wtext(icon::OPEN)
+            .family("second-icons")
+            .add_strong(&mut rsc)
+            .any();
+
+        rsc.draw(&first);
+        rsc.draw(&second);
+        let glyphs_before = rsc.ui.text.borrow().atlas.glyph_count();
+        let pages_before = rsc.ui.text.borrow().atlas.page_count();
+        assert_eq!((glyphs_before, pages_before), (2, 2));
+
+        rsc.ui.replace_font("first-icons", ICON_FONT).unwrap();
+
+        assert_eq!(rsc.ui.text.borrow().atlas.glyph_count(), 1);
+        assert_eq!(rsc.ui.text.borrow().atlas.page_count(), 1);
+        rsc.draw(&first);
+        assert_eq!(rsc.ui.text.borrow().atlas.glyph_count(), 2);
+        assert_eq!(rsc.ui.text.borrow().atlas.page_count(), 2);
+    }
+
     fn cost_of_one_delta(paragraphs: usize) -> (u64, u64) {
         let mut rsc = TestRsc {
             ui: Ui::default(),