use std::ops::Range; use crate::{    geometry::{        rect::RectF,        vector::{vec2f, Vector2F},    },    json::{json, ToJson},    LayoutContext, PaintContext, SceneBuilder, ViewContext,};use crate::{Element, SizeConstraint}; #[derive(Default)]pub struct Empty {    collapsed: bool,} impl Empty {    pub fn new() -> Self {        Self::default()    }     pub fn collapsed(mut self) -> Self {        self.collapsed = true;        self    }} impl<V: 'static> Element<V> for Empty {    type LayoutState = ();    type PaintState = ();     fn layout(        &mut self,        constraint: SizeConstraint,        _: &mut V,        _: &mut LayoutContext<V>,    ) -> (Vector2F, Self::LayoutState) {        let x = if constraint.max.x().is_finite() && !self.collapsed {            constraint.max.x()        } else {            constraint.min.x()        };        let y = if constraint.max.y().is_finite() && !self.collapsed {            constraint.max.y()        } else {            constraint.min.y()        };         (vec2f(x, y), ())    }     fn paint(        &mut self,        _: &mut SceneBuilder,        _: RectF,        _: RectF,        _: &mut Self::LayoutState,        _: &mut V,        _: &mut PaintContext<V>,    ) -> Self::PaintState {    }     fn rect_for_text_range(        &self,        _: Range<usize>,        _: RectF,        _: RectF,        _: &Self::LayoutState,        _: &Self::PaintState,        _: &V,        _: &ViewContext<V>,    ) -> Option<RectF> {        None    }     fn debug(        &self,        bounds: RectF,        _: &Self::LayoutState,        _: &Self::PaintState,        _: &V,        _: &ViewContext<V>,    ) -> serde_json::Value {        json!({            "type": "Empty",            "bounds": bounds.to_json(),        })    }}