ListView: fix continuous redraw with fluent style

Because we set the viewport-width several time to different value during
the layouting of the ListView, it will cause this property to always be
dirty. In particular, this causes permanent restart of the fluent's
scrollbar animation on the size of the handle, causing continous
repaints.

api/cpp/include/slint.h

@@ -1237,12 +1237,13 @@ class Repeater
                                   float listview_width, float viewport_y) const
     {
         float offset = viewport_y;
-        viewport_width->set(listview_width);
+        auto vp_width = listview_width;
         if (!inner)
             return offset;
         for (auto &x : inner->data) {
-            (*x.ptr)->listview_layout(&offset, viewport_width);
+            vp_width = std::max(vp_width, (*x.ptr)->listview_layout(&offset));
         }
+        viewport_width->set(vp_width);
         return offset;
     }
 

internal/compiler/generator/cpp.rs

@@ -2493,18 +2493,12 @@ fn generate_repeated_component(
             Access::Public, // Because Repeater accesses it
             Declaration::Function(Function {
                 name: "listview_layout".into(),
-                signature:
-                    "(float *offset_y, const slint::private_api::Property<float> *viewport_width) const -> void"
-                        .to_owned(),
+                signature: "(float *offset_y) const -> float".to_owned(),
                 statements: Some(vec![
                     "[[maybe_unused]] auto self = this;".into(),
-                    "float vp_w = viewport_width->get();".to_owned(),
-
-                    format!("{}.set(*offset_y);", p_y), // FIXME: shouldn't that be handled by apply layout?
+                    format!("{}.set(*offset_y);", p_y),
                     format!("*offset_y += {}.get();", p_height),
-                    format!("float w = {}.get();", p_width),
-                    "if (vp_w < w)".to_owned(),
-                    "    viewport_width->set(w);".to_owned(),
+                    format!("return {}.get();", p_width),
                 ]),
                 ..Function::default()
             }),

internal/compiler/generator/rust.rs

@@ -1773,16 +1773,11 @@ fn generate_repeated_component(
             fn listview_layout(
                 self: core::pin::Pin<&Self>,
                 offset_y: &mut sp::LogicalLength,
-                viewport_width: core::pin::Pin<&sp::Property<sp::LogicalLength>>,
-            ) {
+            ) -> sp::LogicalLength {
                 let _self = self;
-                let vp_w = viewport_width.get();
                 #p_y.set(*offset_y);
                 *offset_y += #p_height.get();
-                let w = #p_width.get();
-                if vp_w < w {
-                    viewport_width.set(w);
-                }
+                #p_width.get()
             }
         }
     } else {

internal/core/model.rs

@@ -729,11 +729,10 @@ pub trait RepeatedItemTree:
     ///
     /// offset_y is the `y` position where this item should be placed.
     /// it should be updated to be to the y position of the next item.
-    fn listview_layout(
-        self: Pin<&Self>,
-        _offset_y: &mut LogicalLength,
-        _viewport_width: Pin<&Property<LogicalLength>>,
-    ) {
+    ///
+    /// Returns the item width
+    fn listview_layout(self: Pin<&Self>, _offset_y: &mut LogicalLength) -> LogicalLength {
+        LogicalLength::default()
     }
 
     /// Returns what's needed to perform the layout if this ItemTrees is in a box layout
@@ -971,15 +970,15 @@ impl<C: RepeatedItemTree + 'static> Repeater<C> {
         self.data().project_ref().is_dirty.get();
         self.data().project_ref().is_dirty.set(false);
 
-        viewport_width.set(listview_width);
+        let mut vp_width = listview_width;
         let model = self.model();
         let row_count = model.row_count();
         let zero = LogicalLength::zero();
         if row_count == 0 {
             self.0.inner.borrow_mut().instances.clear();
             viewport_height.set(zero);
             viewport_y.set(zero);
-
+            viewport_width.set(vp_width);
             return;
         }
 
@@ -1136,7 +1135,7 @@ impl<C: RepeatedItemTree + 'static> Repeater<C> {
                     c.0 = RepeatedInstanceState::Clean;
                 }
                 if let Some(x) = c.1.as_ref() {
-                    x.as_pin_ref().listview_layout(&mut y, viewport_width);
+                    vp_width = vp_width.max(x.as_pin_ref().listview_layout(&mut y));
                 }
                 idx += 1;
                 if y >= listview_height {
@@ -1150,7 +1149,7 @@ impl<C: RepeatedItemTree + 'static> Repeater<C> {
                 if let Some(data) = model.row_data(idx) {
                     new_instance.update(idx, data);
                 }
-                new_instance.as_pin_ref().listview_layout(&mut y, viewport_width);
+                vp_width = vp_width.max(new_instance.as_pin_ref().listview_layout(&mut y));
                 indices_to_init.push(inner.instances.len());
                 inner.instances.push((RepeatedInstanceState::Clean, Some(new_instance)));
                 idx += 1;
@@ -1190,6 +1189,7 @@ impl<C: RepeatedItemTree + 'static> Repeater<C> {
             inner.cached_item_height = (y - new_offset_y) / inner.instances.len() as Coord;
             inner.anchor_y = inner.cached_item_height * inner.offset as Coord;
             viewport_height.set(inner.cached_item_height * row_count as Coord);
+            viewport_width.set(vp_width);
             let new_viewport_y = -inner.anchor_y + new_offset_y;
             viewport_y.set(new_viewport_y);
             inner.previous_viewport_y = new_viewport_y;

internal/interpreter/dynamic_item_tree.rs

@@ -138,11 +138,7 @@ impl RepeatedItemTree for ErasedItemTreeBox {
         self.run_setup_code();
     }
 
-    fn listview_layout(
-        self: Pin<&Self>,
-        offset_y: &mut LogicalLength,
-        viewport_width: Pin<&Property<LogicalLength>>,
-    ) {
+    fn listview_layout(self: Pin<&Self>, offset_y: &mut LogicalLength) -> LogicalLength {
         generativity::make_guard!(guard);
         let s = self.unerase(guard);
 
@@ -177,10 +173,7 @@ impl RepeatedItemTree for ErasedItemTreeBox {
         let h = LogicalLength::new(h);
         let w = LogicalLength::new(w);
         *offset_y += h;
-        let vp_w = viewport_width.get();
-        if vp_w < w {
-            viewport_width.set(w);
-        }
+        w
     }
 
     fn box_layout_data(self: Pin<&Self>, o: Orientation) -> BoxLayoutCellData {