Encountered some difficulties while adding dashed line support to Path.

[lzm-build]

• internal/compiler/builtins.slint:

// ......
export component Path {
    in property <brush> fill;
    in property <FillRule> fill-rule;
    in property <brush> stroke;
    in property <length> stroke-width;
    in property <LineCap> stroke-line-cap;
    in property <LineJoin> stroke-line-join;
    in property <[length]> stroke-dash-array; // <- Add
    in property <length> stroke-dash-offset; // <- Add
    in property <string> commands;  // 'fake' hardcoded in typeregister.rs
    in property <float> viewbox-x;
    in property <float> viewbox-y;
    in property <float> viewbox-width;
    in property <float> viewbox-height;
    in property <ImageFit> fit-style: contain;
    in property <bool> clip;
    in property <bool> anti-alias: true;

    //-disallow_global_types_as_child_elements
    MoveTo { }

    LineTo { }

    ArcTo { }

    CubicTo { }

    QuadraticTo { }

    Close { }

    //-default_size_binding:expands_to_parent_geometry
}
// ......

• internal/core/items/path.rs

// ......
/// The implementation of the `Path` element
#[repr(C)]
#[derive(FieldOffsets, Default, SlintElement)]
#[pin]
pub struct Path {
    pub elements: Property<PathData>,
    pub fill: Property<Brush>,
    pub fill_rule: Property<FillRule>,
    pub stroke: Property<Brush>,
    pub stroke_width: Property<LogicalLength>,
    pub stroke_line_cap: Property<LineCap>,
    pub stroke_line_join: Property<LineJoin>,
    pub stroke_dash_array: Property<ModelRc<LogicalLength>>, // <- Add
    pub stroke_dash_offset: Property<LogicalLength>, // <- Add
    pub viewbox_x: Property<f32>,
    pub viewbox_y: Property<f32>,
    pub viewbox_width: Property<f32>,
    pub viewbox_height: Property<f32>,
    pub fit_style: Property<ImageFit>,
    pub clip: Property<bool>,
    pub anti_alias: Property<bool>,
    pub cached_rendering_data: CachedRenderingData,
}
// ......

• error message:

error[E0277]: the trait bound `ModelRc<Length<f32, LogicalPx>>: From<Value>` is not satisfied
   --> internal/core/items/path.rs:39:33
    |
 39 | #[derive(FieldOffsets, Default, SlintElement)]
    |                                 ^^^^^^^^^^^^ unsatisfied trait bound
    |
help: the trait `From<Value>` is not implemented for `ModelRc<Length<f32, LogicalPx>>`
   --> internal/core/model.rs:702:1
    |
702 | pub struct ModelRc<T>(Option<Rc<dyn Model<Data = T>>>);
    | ^^^^^^^^^^^^^^^^^^^^^
    = note: required for `Value` to implement `Into<ModelRc<Length<f32, LogicalPx>>>`
    = note: required for `ModelRc<Length<f32, LogicalPx>>` to implement `TryFrom<Value>`
    = note: required for `Value` to implement `TryInto<ModelRc<Length<f32, LogicalPx>>>`
note: required for `vtable::FieldOffset<items::path::Path, properties::Property<ModelRc<Length<f32, LogicalPx>>>, AllowPin>` to implement `rtti::PropertyInfo<items::path::Path, Value>`
   --> internal/core/rtti.rs:156:31
    |
156 | impl<Item: 'static, T, Value> PropertyInfo<Item, Value> for FieldOffset<Item, Property<T>>
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
157 | where
158 |     Value: TryInto<T> + Clone + PartialEq + Default + 'static,
    |            ---------- unsatisfied trait bound introduced here
    = note: this error originates in the derive macro `SlintElement` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `Value: From<ModelRc<Length<f32, LogicalPx>>>` is not satisfied
   --> internal/core/items/path.rs:39:33
    |
 39 | #[derive(FieldOffsets, Default, SlintElement)]
    |                                 ^^^^^^^^^^^^ the trait `From<ModelRc<Length<f32, LogicalPx>>>` is not implemented for `Value`
    |
    = note: required for `ModelRc<Length<f32, LogicalPx>>` to implement `Into<Value>`
    = note: required for `Value` to implement `TryFrom<ModelRc<Length<f32, LogicalPx>>>`
    = note: required for `ModelRc<Length<f32, LogicalPx>>` to implement `TryInto<Value>`
note: required for `vtable::FieldOffset<items::path::Path, properties::Property<ModelRc<Length<f32, LogicalPx>>>, AllowPin>` to implement `rtti::PropertyInfo<items::path::Path, Value>`
   --> internal/core/rtti.rs:156:31
    |
156 | impl<Item: 'static, T, Value> PropertyInfo<Item, Value> for FieldOffset<Item, Property<T>>
    |                               ^^^^^^^^^^^^^^^^^^^^^^^^^     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...
159 |     T: TryInto<Value> + Clone + PartialEq + Default + 'static,
    |        -------------- unsatisfied trait bound introduced here
    = note: this error originates in the derive macro `SlintElement` (in Nightly builds, run with -Z macro-backtrace for more info)

Hello everyone! I encountered the error above while adding dashed line support to Path. How should I handle <[length]> correctly?

[ogoffart]

Thanks for trying to contribute.

Indeed, we currently can't have builtin properties with a "model" type.
That's because ModelRc also can't be shared in C++ as is (where it is a shared_ptr)

So to move forward i can see the following solution:

• Do not use stroke-dash-array property, but an stroke-style property that would be an enum (Solid, Dashed, Dotted) or something like that.
• Use Property<SharedVector<f32>> but that comes with its own challenge (it is still not supported out of the box and there will be need to have compiler support to generate it)

[lzm-build]

• internal/core/rtti.rs

// ......
macro_rules! declare_ValueType_2 {
    ($( $(#[$enum_doc:meta])* enum $Name:ident { $($body:tt)* })*) => {
        declare_ValueType![
            (),
            bool,
            u32,
            u64,
            i32,
            i64,
            f32,
            f64,
            crate::SharedString,
            crate::graphics::Image,
            crate::Color,
            crate::PathData,
            crate::animations::EasingCurve,
            crate::items::StandardListViewItem,
            crate::items::TableColumn,
            crate::input::KeyEvent,
            crate::Brush,
            crate::graphics::Point,
            crate::items::PointerEvent,
            crate::items::PointerScrollEvent,
            crate::lengths::LogicalLength,
            crate::lengths::LogicalPoint,
            crate::lengths::LogicalSize,
            crate::lengths::LogicalEdges,
            crate::component_factory::ComponentFactory,
            crate::api::LogicalPosition,
            crate::items::FontMetrics,
            crate::items::MenuEntry,
            crate::items::DropEvent,
            crate::model::ModelRc<crate::items::MenuEntry>,
            crate::styled_text::StyledText,
            crate::input::Keys,
            crate::model::ModelRc<crate::lengths::LogicalLength>, // <- Add
            $(crate::items::$Name,)*
        ];
    };
}
// ......

After I made the above changes, cargo check didn’t report errors. I looked into the compiler handles slint files in rust and noticed that it uses ModelRc to replace Array. If I replaced it with SharedVector, it seems like it wouldn’t quite match?

[ogoffart]

Yes, you will get further like that with ModelRc But the problem will be that the C++ binding will fail

[lzm-build]

After trying it out, I did run into the error you mentioned:

ninja: Entering directory `./build/'
[2/4] Building CXX object CMakeFiles/gallery.dir/main.cpp.o
FAILED: CMakeFiles/gallery.dir/main.cpp.o 
/usr/bin/c++ -DHAVE_GETTEXT -DSRC_DIR=\"/home/lzm/RustroverProjects/dev/slint/examples/gallery\" -I/home/lzm/RustroverProjects/dev/slint/examples/gallery/build -isystem /home/lzm/RustroverProjects/dev/slint/installed/include/slint -std=gnu++20 -MD -MT CMakeFiles/gallery.dir/main.cpp.o -MF CMakeFiles/gallery.dir/main.cpp.o.d -o CMakeFiles/gallery.dir/main.cpp.o -c /home/lzm/RustroverProjects/dev/slint/examples/gallery/main.cpp
In file included from /home/lzm/RustroverProjects/dev/slint/installed/include/slint/private/slint_internal.h:14,
                 from /home/lzm/RustroverProjects/dev/slint/installed/include/slint/slint.h:6,
                 from /home/lzm/RustroverProjects/dev/slint/examples/gallery/build/gallery.h:5,
                 from /home/lzm/RustroverProjects/dev/slint/examples/gallery/main.cpp:4:
/home/lzm/RustroverProjects/dev/slint/installed/include/slint/private/slint_properties.h: In instantiation of ‘struct slint::private_api::Property<slint::cbindgen_private::ModelRc<float> >’:
/home/lzm/RustroverProjects/dev/slint/installed/include/slint/private/slint_internal.h:1384:30:   required from here
 1384 |     Property<ModelRc<float>> stroke_dash_array;
      |                              ^~~~~~~~~~~~~~~~~
/home/lzm/RustroverProjects/dev/slint/installed/include/slint/private/slint_properties.h:230:15: error: ‘slint::private_api::Property<T>::value’ has incomplete type
  230 |     mutable T value {};
      |               ^~~~~
/home/lzm/RustroverProjects/dev/slint/installed/include/slint/private/slint_internal.h:278:8: note: declaration of ‘struct slint::cbindgen_private::ModelRc<float>’
  278 | struct ModelRc;
      |        ^~~~~~~
[3/4] Building CXX object CMakeFiles/gallery.dir/slint_generated_gallery_1.cpp.o
FAILED: CMakeFiles/gallery.dir/slint_generated_gallery_1.cpp.o 
/usr/bin/c++ -DHAVE_GETTEXT -DSRC_DIR=\"/home/lzm/RustroverProjects/dev/slint/examples/gallery\" -I/home/lzm/RustroverProjects/dev/slint/examples/gallery/build -isystem /home/lzm/RustroverProjects/dev/slint/installed/include/slint -std=gnu++20 -MD -MT CMakeFiles/gallery.dir/slint_generated_gallery_1.cpp.o -MF CMakeFiles/gallery.dir/slint_generated_gallery_1.cpp.o.d -o CMakeFiles/gallery.dir/slint_generated_gallery_1.cpp.o -c /home/lzm/RustroverProjects/dev/slint/examples/gallery/build/slint_generated_gallery_1.cpp
In file included from /home/lzm/RustroverProjects/dev/slint/installed/include/slint/private/slint_internal.h:14,
                 from /home/lzm/RustroverProjects/dev/slint/installed/include/slint/slint.h:6,
                 from /home/lzm/RustroverProjects/dev/slint/examples/gallery/build/gallery.h:5,
                 from /home/lzm/RustroverProjects/dev/slint/examples/gallery/build/slint_generated_gallery_1.cpp:2:
/home/lzm/RustroverProjects/dev/slint/installed/include/slint/private/slint_properties.h: In instantiation of ‘struct slint::private_api::Property<slint::cbindgen_private::ModelRc<float> >’:
/home/lzm/RustroverProjects/dev/slint/installed/include/slint/private/slint_internal.h:1384:30:   required from here
 1384 |     Property<ModelRc<float>> stroke_dash_array;
      |                              ^~~~~~~~~~~~~~~~~
/home/lzm/RustroverProjects/dev/slint/installed/include/slint/private/slint_properties.h:230:15: error: ‘slint::private_api::Property<T>::value’ has incomplete type
  230 |     mutable T value {};
      |               ^~~~~
/home/lzm/RustroverProjects/dev/slint/installed/include/slint/private/slint_internal.h:278:8: note: declaration of ‘struct slint::cbindgen_private::ModelRc<float>’
  278 | struct ModelRc;
      |        ^~~~~~~
ninja: build stopped: subcommand failed.

I looked at the Cpp part of the compiler impl, it uses std::shared_ptr<slint::Model<{}>> to represent Array. This works fine for Array in external slint files because it can construct the correct type in cpp side. However, for Array in builtins.slint, the type in rust is determined as ModelRc<>, which causes this mismatch. Is my understanding correct?

Is it feasible to directly change ModelRc to SharedVector for the Array type in the part of the compiler that generates rust code from slint file?