Field scrub: the field senses drags only with Alt held or a scrub going on, so a touch swipe stays the scroll area's

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

crates/ui-egui/src/field_tests.rs

@@ -1216,11 +1216,11 @@ fn alt_held_over_a_field_scrubs_it() {
     drag(&mut u, at, 25.0, Modifiers::NONE);
     assert_eq!(geom(&u, a).0, 35.0, "without Alt the field doesn't scrub");
     assert_eq!(undo_steps(&u), steps + 1);
-    // Alt and the press in the same frame still scrub, and Alt let go before the button still
-    // ends the scrub with its undo step.
+    // Alt let go before the button still ends the scrub with its undo step.
     let (at, _) = field(&mut u, "X");
     let press = |pressed: bool, m: Modifiers, p: Pos2| Event::PointerButton { pos: p, button: egui::PointerButton::Primary, pressed, modifiers: m };
-    u.frame_with(vec![Event::PointerMoved(at), press(true, alt, at)], alt);
+    u.frame_with(vec![Event::PointerMoved(at)], alt);
+    u.frame_with(vec![press(true, alt, at)], alt);
     for k in 1..=10 {
         u.frame_with(vec![Event::PointerMoved(pos2(at.x + 2.0 * k as f32, at.y))], alt);
     }
@@ -1229,4 +1229,24 @@ fn alt_held_over_a_field_scrubs_it() {
     u.frame(vec![]);
     assert_eq!(geom(&u, a).0, 55.0, "twenty more");
     assert_eq!(undo_steps(&u), steps + 2, "committed when the button went up, without Alt");
+    // Without Alt the field doesn't take the drag at all (a touch swipe over it is the panel's to
+    // scroll): the press is a click of the field's, not a drag.
+    let (at, _) = field(&mut u, "X");
+    let field_id = Id::unique("pos_x").with("field");
+    u.frame_with(vec![Event::PointerMoved(at)], Modifiers::NONE);
+    u.frame_with(vec![press(true, Modifiers::NONE, at)], Modifiers::NONE);
+    u.frame_with(vec![Event::PointerMoved(pos2(at.x + 10.0, at.y))], Modifiers::NONE);
+    assert!(!u.ctx.is_being_dragged(field_id), "a plain press on the field isn't a drag of the field's");
+    u.frame_with(vec![Event::PointerMoved(pos2(at.x + 10.0, at.y)), press(false, Modifiers::NONE, pos2(at.x + 10.0, at.y))], Modifiers::NONE);
+    u.frame(vec![]);
+    assert_eq!(geom(&u, a).0, 55.0, "nothing scrubbed");
+    // With Alt held over it, the field does take the drag.
+    let (at, _) = field(&mut u, "X");
+    u.frame_with(vec![Event::PointerMoved(at)], alt);
+    u.frame_with(vec![press(true, alt, at)], alt);
+    u.frame_with(vec![Event::PointerMoved(pos2(at.x + 10.0, at.y))], alt);
+    assert!(u.ctx.is_being_dragged(field_id), "with Alt the drag is the field's");
+    u.frame_with(vec![Event::PointerMoved(pos2(at.x + 10.0, at.y)), press(false, alt, pos2(at.x + 10.0, at.y))], alt);
+    u.frame(vec![]);
+    assert_eq!(geom(&u, a).0, 65.0, "ten more");
 }

crates/ui-egui/src/widgets.rs

@@ -268,15 +268,17 @@ fn number_field_impl(
     let mut editing: Option<String> = ui.data(|d| d.get_temp(editing_id));
     // Alt held over the field scrubs it too, as the label always does: "hover the input field
     // itself and hold down the modifier key" (Adjust alignment, rotation, position, and
-    // dimensions). The field always senses drags (egui assigns a press by the frame before it, so
-    // a sense that waits for Alt would miss a press that arrives with it); Alt as the drag begins
-    // is what makes it a scrub, and that holds until the button is let go, Alt released or not.
+    // dimensions). The field senses drags only while Alt is held, or while a scrub begun that way
+    // goes on (Alt released or not), so a plain press or a touch swipe on it stays the scroll
+    // area's; egui assigns a press by the frame before it, so Alt is held over the field before
+    // the press, as a hand does. Alt as the drag begins is what makes it a scrub.
     let field_id = id.with("field");
-    let field_resp = ui.interact(edit_rect, field_id, Sense::click_and_drag());
     let alt_now = ui.input(|i| i.modifiers.alt);
     let scrubbing_id = id.with("altscrub");
-    let alt_scrub =
-        editing.is_none() && if field_resp.drag_started() { alt_now } else { ui.data(|d| d.get_temp::<bool>(scrubbing_id)).unwrap_or(false) };
+    let scrubbing = ui.data(|d| d.get_temp::<bool>(scrubbing_id)).unwrap_or(false);
+    let field_sense = if editing.is_none() && (alt_now || scrubbing) { Sense::click_and_drag() } else { Sense::click() };
+    let field_resp = ui.interact(edit_rect, field_id, field_sense);
+    let alt_scrub = editing.is_none() && if field_resp.drag_started() { alt_now } else { scrubbing };
     ui.data_mut(|d| d.insert_temp(scrubbing_id, alt_scrub && field_resp.dragged() && !field_resp.drag_stopped()));
     a11y::number(&field_resp, lead.name(), value, suffix, empty.text());
     a11y::ring_around(ui, rect, &field_resp);