Merge #568: Fix #563: the font menu's live preview no longer flickers

# Conflicts:
#	ROADMAP.md
#	crates/ui-egui/src/tests_font_menu.rs

crates/ui-egui/src/font_menu.rs

@@ -134,6 +134,10 @@ struct MenuState {
     /// The pass the list was last drawn in, and the pass it opened in.
     last: u64,
     opened: u64,
+    /// The family the text had as the menu opened. A preview shows another one in the document
+    /// (and the menu's caller), but this one stays the current family: hovering it ends the
+    /// preview (#563).
+    current: String,
     /// The highlighted row and the query and filters it belongs to.
     highlight: Option<usize>,
     query: String,
@@ -194,6 +198,7 @@ fn list(ui: &mut Ui, state_id: egui::Id, st: &mut MenuState, current: &str, samp
         st.opened = pass;
         st.highlight = None;
         st.query.clear();
+        st.current = current.to_string();
     }
     st.last = pass;
     // For [`end_stale_preview`]: the menu is open, in this layer.
@@ -243,8 +248,9 @@ fn list(ui: &mut Ui, state_id: egui::Id, st: &mut MenuState, current: &str, samp
     });
     let enter = ui.input(|i| i.key_pressed(egui::Key::Enter));
     let db = vectorcraft_text::FontDb::global();
-    // The current family by its own name (a document may name it in Japanese: ヒラギノ角ゴシック).
-    let current = db.canonical(current, "").0;
+    // The current family by its own name (a document may name it in Japanese: ヒラギノ角ゴシック),
+    // as it was before any preview.
+    let current = db.canonical(&st.current, "").0;
     let current = current.as_str();
     let favorite = |f: &str| look.favorites.iter().any(|x| x.eq_ignore_ascii_case(f));
     // The generation is read first: fonts that load meanwhile make the next frame list them.

crates/ui-egui/src/tests_font_menu.rs

@@ -318,3 +318,61 @@ fn the_search_field_stays_put_while_the_list_scrolls() {
         }
     }
 }
+
+/// #563: a preview stays on the text while the menu stays on its family. The menu's caller passes
+/// the text's font, which the preview changed; the menu keeps the font from before the preview as
+/// the current one, so it doesn't take the previewed family for it and end the preview, then
+/// preview it again, every frame (the text flickered).
+#[test]
+fn a_preview_stays_put_while_the_menu_is_still() {
+    let ctx = egui::Context::default();
+    crate::theme::install_fonts(&ctx);
+    let mut app = VectorcraftApp::new(Session::new(), Default::default());
+    app.run("file.new", json!({"width": 300, "height": 200})).unwrap();
+    let id = app.session.execute("text.create", &json!({"x": 20, "y": 50, "text": "Gagaku", "font": "Inter"})).unwrap()["id"].as_u64().unwrap();
+    app.session.execute("select.set", &json!({"ids": [id]})).unwrap();
+    let font = |app: &VectorcraftApp| match &app.session.active().unwrap().doc.node(vectorcraft_doc::NodeId(id)).unwrap().kind {
+        NodeKind::Text(t) => t.first_style().font_family,
+        _ => String::new(),
+    };
+    let revision = |app: &VectorcraftApp| app.session.active().unwrap().revision;
+    // A panel's frame: the menu shows the text's font, and what it picks is applied.
+    let frame = |app: &mut VectorcraftApp, events: Vec<egui::Event>| {
+        let input =
+            egui::RawInput { events, screen_rect: Some(egui::Rect::from_min_size(egui::Pos2::ZERO, egui::vec2(600.0, 800.0))), ..Default::default() };
+        let current = font(app);
+        let (mut at, mut picked) = (egui::Pos2::ZERO, None);
+        let mut out = ctx.run_ui(input, |ui| {
+            crate::font_menu::end_stale_preview(app, ui.ctx());
+            at = ui.next_widget_position();
+            picked = font_menu(ui, "test-steady", &current, 260.0, None, MenuLook::default());
+            if let Some(p) = picked.clone() {
+                crate::font_menu::apply(app, ui.ctx(), p);
+            }
+        });
+        out.textures_delta.clear();
+        (at, picked)
+    };
+    let (at, _) = frame(&mut app, vec![]);
+    let click = at + egui::vec2(40.0, 10.0);
+    let button = |pressed| egui::Event::PointerButton { pos: click, button: egui::PointerButton::Primary, pressed, modifiers: Default::default() };
+    frame(&mut app, vec![egui::Event::PointerMoved(click), button(true)]);
+    frame(&mut app, vec![button(false)]);
+    for _ in 0..5 {
+        frame(&mut app, vec![]);
+    }
+    let (_, picked) = frame(&mut app, key(egui::Key::ArrowDown));
+    assert!(matches!(picked, Some(FontPick::Preview(..))), "{picked:?}");
+    let previewed = font(&app);
+    assert_ne!(previewed, "Inter");
+    let rev = revision(&app);
+    for _ in 0..6 {
+        let (_, picked) = frame(&mut app, vec![]);
+        assert_eq!(picked, None, "nothing more to apply");
+    }
+    assert_eq!((font(&app), revision(&app)), (previewed, rev), "the preview stays, untouched");
+    // Back on the text's own family, the preview ends.
+    let (_, picked) = frame(&mut app, key(egui::Key::ArrowUp));
+    assert_eq!(picked, Some(FontPick::EndPreview));
+    assert_eq!(font(&app), "Inter");
+}