Support default-font-* properties in Live-Preview

... by changing the resolution for the `WindowItem` to traverse the
item tree from the current item, instead of going to the window.

This doesn't quite fix #4298 because `rem` resolution is still missing.
That requires the built-in default font size function to be fixed as
well, which is non-trivial.

cc #4298

internal/backends/qt/qt_widgets/button.rs

@@ -202,6 +202,8 @@ impl Item for NativeButton {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let standard_button_kind = self.actual_standard_button_kind();
         let mut text: qttypes::QString = self.actual_text(standard_button_kind);

internal/backends/qt/qt_widgets/checkbox.rs

@@ -35,6 +35,8 @@ impl Item for NativeCheckBox {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let text: qttypes::QString = self.text().as_str().into();
         let widget: NonNull<()> = SlintTypeErasedWidgetPtr::qwidget_ptr(&self.widget_ptr);

internal/backends/qt/qt_widgets/combobox.rs

@@ -32,6 +32,8 @@ impl Item for NativeComboBox {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let widget: NonNull<()> = SlintTypeErasedWidgetPtr::qwidget_ptr(&self.widget_ptr);
         let size = cpp!(unsafe [widget as "QWidget*"] -> qttypes::QSize as "QSize" {
@@ -172,6 +174,8 @@ impl Item for NativeComboBoxPopup {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         Default::default()
     }

internal/backends/qt/qt_widgets/groupbox.rs

@@ -146,6 +146,8 @@ impl Item for NativeGroupBox {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let text: qttypes::QString = self.title().as_str().into();
 

internal/backends/qt/qt_widgets/lineedit.rs

@@ -76,6 +76,8 @@ impl Item for NativeLineEdit {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let min = match orientation {
             Orientation::Horizontal => self.native_padding_left() + self.native_padding_right(),

internal/backends/qt/qt_widgets/listviewitem.rs

@@ -38,6 +38,8 @@ impl Item for NativeStandardListViewItem {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let index: i32 = self.index();
         let item = self.item();

internal/backends/qt/qt_widgets/progress_indicator.rs

@@ -30,6 +30,8 @@ impl Item for NativeProgressIndicator {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let indeterminate = self.indeterminate();
         let progress =

internal/backends/qt/qt_widgets/scrollview.rs

@@ -93,6 +93,8 @@ impl Item for NativeScrollView {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let min = match orientation {
             Orientation::Horizontal => self.native_padding_left() + self.native_padding_right(),

internal/backends/qt/qt_widgets/slider.rs

@@ -78,6 +78,8 @@ impl Item for NativeSlider {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let enabled = self.enabled();
         // Slint slider supports floating point ranges, while Qt uses integer. To support (0..1) ranges

internal/backends/qt/qt_widgets/spinbox.rs

@@ -73,6 +73,8 @@ impl Item for NativeSpinBox {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         //let value: i32 = self.value();
         let data = self.data();

internal/backends/qt/qt_widgets/tableheadersection.rs

@@ -29,6 +29,8 @@ impl Item for NativeTableHeaderSection {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let index: i32 = self.index();
         let item = self.item();

internal/backends/qt/qt_widgets/tabwidget.rs

@@ -178,6 +178,8 @@ impl Item for NativeTabWidget {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let (content_size, tabbar_size) = match orientation {
             Orientation::Horizontal => (
@@ -355,6 +357,8 @@ impl Item for NativeTab {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<i_slint_core::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let text: qttypes::QString = self.title().as_str().into();
         let icon: qttypes::QPixmap =

internal/backends/qt/qt_window.rs

@@ -673,14 +673,14 @@ impl ItemRenderer for QtItemRenderer<'_> {
     fn draw_text(
         &mut self,
         text: Pin<&dyn RenderText>,
-        _: &ItemRc,
+        self_rc: &ItemRc,
         size: LogicalSize,
         _: &CachedRenderingData,
     ) {
         let rect: qttypes::QRectF = check_geometry!(size);
         let fill_brush: qttypes::QBrush = into_qbrush(text.color(), rect.width, rect.height);
         let mut string: qttypes::QString = text.text().as_str().into();
-        let font: QFont = get_font(text.font_request(WindowInner::from_pub(self.window)));
+        let font: QFont = get_font(text.font_request(self_rc));
         let (horizontal_alignment, vertical_alignment) = text.alignment();
         let alignment = match horizontal_alignment {
             TextHorizontalAlignment::Left => key_generated::Qt_AlignmentFlag_AlignLeft,
@@ -850,14 +850,13 @@ impl ItemRenderer for QtItemRenderer<'_> {
     fn draw_text_input(
         &mut self,
         text_input: Pin<&items::TextInput>,
-        _: &ItemRc,
+        self_rc: &ItemRc,
         size: LogicalSize,
     ) {
         let rect: qttypes::QRectF = check_geometry!(size);
         let fill_brush: qttypes::QBrush = into_qbrush(text_input.color(), rect.width, rect.height);
 
-        let font: QFont =
-            get_font(text_input.font_request(&WindowInner::from_pub(self.window).window_adapter()));
+        let font: QFont = get_font(text_input.font_request(self_rc));
         let flags = match text_input.horizontal_alignment() {
             TextHorizontalAlignment::Left => key_generated::Qt_AlignmentFlag_AlignLeft,
             TextHorizontalAlignment::Center => key_generated::Qt_AlignmentFlag_AlignHCenter,

internal/compiler/generator/cpp.rs

@@ -3814,8 +3814,9 @@ fn compile_builtin_function_call(
         BuiltinFunction::ImplicitLayoutInfo(orient) => {
             if let [llr::Expression::PropertyReference(pr)] = arguments {
                 let native = native_item(pr, ctx);
+                let item_rc = access_item_rc(pr, ctx);
                 format!(
-                    "{vt}->layout_info({{{vt}, const_cast<slint::cbindgen_private::{ty}*>(&{i})}}, {o}, &{window})",
+                    "{vt}->layout_info({{{vt}, const_cast<slint::cbindgen_private::{ty}*>(&{i})}}, {o}, &{window}, &{item_rc})",
                     vt = native.cpp_vtable_getter,
                     ty = native.class_name,
                     o = to_cpp_orientation(orient),

internal/compiler/generator/rust.rs

@@ -2111,8 +2111,11 @@ fn access_window_adapter_field(ctx: &EvaluationContext) -> TokenStream {
 }
 
 /// Given a property reference to a native item (eg, the property name is empty)
-/// return tokens to the `ItemRc`
-fn access_item_rc(pr: &llr::PropertyReference, ctx: &EvaluationContext) -> TokenStream {
+/// return tokens to the VRc for the item tree and the item index.
+fn access_item_by_item_tree_and_index(
+    pr: &llr::PropertyReference,
+    ctx: &EvaluationContext,
+) -> (TokenStream, TokenStream) {
     let mut ctx = ctx;
     let mut component_access_tokens = quote!(_self);
 
@@ -2147,12 +2150,19 @@ fn access_item_rc(pr: &llr::PropertyReference, ctx: &EvaluationContext) -> Token
                 quote!(#component_access_tokens.tree_index_of_first_child.get() + #item_index_in_tree - 1)
             };
 
-            quote!(&sp::ItemRc::new(#component_rc_tokens, #item_index_tokens))
+            (component_rc_tokens, item_index_tokens)
         }
         _ => unreachable!(),
     }
 }
 
+/// Given a property reference to a native item (eg, the property name is empty)
+/// return tokens to the `ItemRc`
+fn access_item_rc(pr: &llr::PropertyReference, ctx: &EvaluationContext) -> TokenStream {
+    let (component_rc_tokens, item_index_tokens) = access_item_by_item_tree_and_index(pr, ctx);
+    quote!(&sp::ItemRc::new(#component_rc_tokens, #item_index_tokens))
+}
+
 fn compile_expression(expr: &Expression, ctx: &EvaluationContext) -> TokenStream {
     match expr {
         Expression::StringLiteral(s) => {
@@ -2849,8 +2859,9 @@ fn compile_builtin_function_call(
                 let item = access_member(pr, ctx);
                 let window_adapter_tokens = access_window_adapter_field(ctx);
                 item.then(|item| {
+                    let (item_tree, item_index) = access_item_by_item_tree_and_index(pr, ctx);
                     quote!(
-                        sp::Item::layout_info(#item, #orient, #window_adapter_tokens)
+                        sp::Item::layout_info(#item, #orient, #window_adapter_tokens, &#item_tree, #item_index)
                     )
                 })
             } else {

internal/core/item_rendering.rs

@@ -14,7 +14,6 @@ use crate::lengths::{
     LogicalVector,
 };
 use crate::properties::PropertyTracker;
-use crate::window::WindowInner;
 use crate::{Brush, Coord, SharedString};
 #[cfg(not(feature = "std"))]
 use alloc::boxed::Box;
@@ -310,7 +309,7 @@ pub trait RenderImage {
 pub trait RenderText {
     fn target_size(self: Pin<&Self>) -> LogicalSize;
     fn text(self: Pin<&Self>) -> SharedString;
-    fn font_request(self: Pin<&Self>, window: &WindowInner) -> FontRequest;
+    fn font_request(self: Pin<&Self>, self_rc: &ItemRc) -> FontRequest;
     fn color(self: Pin<&Self>) -> Brush;
     fn alignment(self: Pin<&Self>) -> (TextHorizontalAlignment, TextVerticalAlignment);
     fn wrap(self: Pin<&Self>) -> TextWrap;

internal/core/item_tree.rs

@@ -714,6 +714,14 @@ impl ItemRc {
         result
     }
 
+    pub fn window_item(&self) -> Option<VRcMapped<ItemTreeVTable, crate::items::WindowItem>> {
+        let root_item_in_local_item_tree = ItemRc::new(self.item_tree.clone(), 0);
+
+        root_item_in_local_item_tree.downcast::<crate::items::WindowItem>().or_else(|| {
+            root_item_in_local_item_tree.parent_item().and_then(|parent| parent.window_item())
+        })
+    }
+
     /// Visit the children of this element and call the visitor to each of them, until the visitor returns [`ControlFlow::Break`].
     /// When the visitor breaks, the function returns the value. If it doesn't break, the function returns None.
     fn visit_descendants_impl<R>(

internal/core/items.rs

@@ -126,6 +126,8 @@ pub struct ItemVTable {
         core::pin::Pin<VRef<ItemVTable>>,
         orientation: Orientation,
         window_adapter: &WindowAdapterRc,
+        self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        self_index: u32,
     ) -> LayoutInfo,
 
     /// Event handler for mouse and touch event. This function is called before being called on children.
@@ -188,6 +190,8 @@ impl Item for Empty {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo { stretch: 1., ..LayoutInfo::default() }
     }
@@ -265,6 +269,8 @@ impl Item for Rectangle {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo { stretch: 1., ..LayoutInfo::default() }
     }
@@ -346,6 +352,8 @@ impl Item for BasicBorderRectangle {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo { stretch: 1., ..LayoutInfo::default() }
     }
@@ -446,6 +454,8 @@ impl Item for BorderRectangle {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo { stretch: 1., ..LayoutInfo::default() }
     }
@@ -561,6 +571,8 @@ impl Item for Clip {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo { stretch: 1., ..LayoutInfo::default() }
     }
@@ -659,6 +671,8 @@ impl Item for Opacity {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo { stretch: 1., ..LayoutInfo::default() }
     }
@@ -763,6 +777,8 @@ impl Item for Layer {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo { stretch: 1., ..LayoutInfo::default() }
     }
@@ -842,6 +858,8 @@ impl Item for Rotate {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo { stretch: 1., ..LayoutInfo::default() }
     }
@@ -969,6 +987,8 @@ impl Item for WindowItem {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo::default()
     }
@@ -1075,6 +1095,8 @@ impl Item for ContextMenu {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo::default()
     }
@@ -1157,6 +1179,8 @@ impl Item for BoxShadow {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo { stretch: 1., ..LayoutInfo::default() }
     }

internal/core/items/component_container.rs

@@ -168,6 +168,8 @@ impl Item for ComponentContainer {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         self.ensure_updated();
         if let Some(rc) = self.item_tree.borrow().clone() {

internal/core/items/flickable.rs

@@ -67,6 +67,8 @@ impl Item for Flickable {
         self: Pin<&Self>,
         _orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo { stretch: 1., ..LayoutInfo::default() }
     }

internal/core/items/image.rs

@@ -49,6 +49,8 @@ impl Item for ImageItem {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         let natural_size = self.source().size();
         LayoutInfo {
@@ -182,6 +184,8 @@ impl Item for ClippedImage {
         self: Pin<&Self>,
         orientation: Orientation,
         _window_adapter: &Rc<dyn WindowAdapter>,
+        _self_component: &vtable::VRc<crate::item_tree::ItemTreeVTable>,
+        _self_index: u32,
     ) -> LayoutInfo {
         LayoutInfo {
             preferred: match orientation {