Title screens scroll a label wider than its button, as vanilla does

Title::draw's button loop drew every title-screen label centred over its own
full width, so a label wider than the button ran over the buttons beside it
(Create World's 590 px World Type label in so_so, Multiplayer's Join Server in
hi_in). AbstractButton.extractDefaultLabel hands the label to
extractScrollingStringOverContents with a 2 px margin, and vanilla slides it
inside the button; the loop now draws through ui::scrolling_text, which is
that helper.

crates/horizon-client/src/title.rs

@@ -461,6 +461,28 @@ pub(crate) struct Button {
     /// `SpriteIconButton.TextAndIcon`: the icon at the right end, the text centred.
     trailing: Option<(&'static str, f32)>,
 }
+impl Button {
+    /// `AbstractButton.extractDefaultLabel`: the label centred with a 2 px
+    /// margin, and slid inside the button when it does not fit
+    /// (`AbstractWidget.extractScrollingStringOverContents`), instead of being
+    /// drawn past it over the buttons beside it (so_so's 590 px World Type
+    /// label on Create World, hi_in's Join Server in the Multiplayer footer).
+    fn draw_label(&self, batch: &mut HudBatch, atlas: &HudAtlas, color: u32) {
+        let label = Text::literal(&self.label);
+        crate::ui::scrolling_text(
+            batch,
+            atlas,
+            &label,
+            self.x + 2.0,
+            self.x + self.w - 2.0,
+            self.y,
+            self.y + 20.0,
+            self.y + 6.0,
+            color,
+        );
+    }
+}
+
 /// Java String.hashCode for text seeds (WorldOptions.parseSeed).
 pub fn parse_seed(text: &str) -> Option<i64> {
     let t = text.trim();
@@ -2991,15 +3013,7 @@ Would you like to enable the Narrator or visit the Accessibility Settings?",
                 );
                 continue;
             }
-            let tw = HudBatch::text_width(atlas, &b.label);
-            batch.text(
-                atlas,
-                &b.label,
-                b.x + (b.w / 2.0).floor() - (tw.ceil() / 2.0).floor(),
-                b.y + 6.0,
-                color,
-                true,
-            );
+            b.draw_label(batch, atlas, color);
             if let Some((icon, size)) = b.trailing {
                 // TextAndIcon: `x + width - spriteWidth - 2`, centred in the height.
                 batch.sprite_scaled(

crates/horizon-client/src/title/tests.rs

@@ -1821,3 +1821,47 @@ fn a_finished_optimization_stamps_the_level_data() {
     let version = root.get("Data").and_then(|d| d.get("DataVersion"));
     assert!(matches!(version, Some(Tag::Int(v)) if *v == horizon_world::DATA_VERSION));
 }
+
+/// `AbstractButton.extractDefaultLabel`: a label too wide for its button is
+/// slid inside it, not drawn centred over the buttons beside it (`so_so`'s
+/// 590 px World Type label on Create World, `hi_in`'s Join Server).
+#[test]
+fn a_button_label_wider_than_its_button_stays_inside_it() {
+    let atlas = HudAtlas::build(std::path::Path::new("/nonexistent/horizon-test-assets")).unwrap();
+    let mut b = Button {
+        x: 100.0,
+        y: 40.0,
+        w: 100.0,
+        label: "Create Backup and Load the World Anyway".into(),
+        enabled: true,
+        id: 40,
+        icon: None,
+        trailing: None,
+    };
+    assert!(HudBatch::text_width(&atlas, &b.label) > b.w - 4.0);
+    let mut batch = HudBatch::new([640, 480]);
+    b.draw_label(&mut batch, &atlas, u32::MAX);
+    assert!(!batch.vertices.is_empty());
+    for v in &batch.vertices {
+        assert!(
+            (b.x + 2.0..=b.x + b.w - 2.0).contains(&v.pos[0])
+                && (b.y..=b.y + 20.0).contains(&v.pos[1]),
+            "label vertex {:?} outside the button",
+            v.pos
+        );
+    }
+    // A label that fits is centred in the button, as `centered_left` does.
+    b.label = "Done".into();
+    let width = HudBatch::text_width(&atlas, &b.label);
+    let mut batch = HudBatch::new([640, 480]);
+    b.draw_label(&mut batch, &atlas, u32::MAX);
+    let lo = batch
+        .vertices
+        .iter()
+        .map(|v| v.pos[0])
+        .fold(f32::INFINITY, f32::min);
+    assert!(
+        (lo - (b.x + 2.0 + (b.w - 4.0) / 2.0 - (width / 2.0).floor())).abs() < 0.001,
+        "a fitting label starts at {lo}"
+    );
+}