frus_widgets/

iconbutton.rs

//! [`IconButton`]: a button holding **one glyph**, in a box as wide as it is tall.
//!
//! It exists because milestone 313 kept finding the same thing. A `Button` is sized for a
//! word — 64 px wide before its label is measured, 24 px of room either side — and a back
//! arrow, a month arrow, a delete cross or a stepper's plus is not a word. Seven call sites
//! in this repository were asking a button to be something it is not, and the reference has
//! had the answer all along: 40 × 40, circular, no fill, the icon in `on_surface_variant`.
//!
//! ```ignore
//! IconButton::new(Icons::CLOSE).label("Remove").on_press(Msg::Delete)
//! IconButton::glyph("\u{2190}").label("Back").on_press(Msg::Pop)
//! IconButton::new(Icons::STAR).selected(starred).on_press(Msg::Star)
//! ```
//!
//! It takes either an icon from the bundled set or a **glyph**, because the set does not
//! cover everything an application draws and a button that only accepts what happens to be
//! bundled is a button that sends people back to `Button`.
//!
//! **A label is not optional in practice.** An icon says nothing to a screen reader, so
//! [`IconButton::label`] is what makes it announceable — the reference's `tooltip`, doing
//! the same job.

use frus_core::{BorderRadius, Color, Point, Rect, Scene, TextStyle};
use frus_layout::{Dimension, Style};

use crate::disabled::{disabled_container, disabled_content};
use crate::icons::IconData;
use crate::interaction::Status;
use crate::theme::{TapTarget, Theme};
use crate::widget::Widget;

/// The box: as wide as it is tall.
pub const ICON_BUTTON_SIZE: f32 = 40.0;
/// The glyph inside it.
pub const ICON_BUTTON_ICON_SIZE: f32 = 24.0;
/// An outlined icon button's outline.
pub const ICON_BUTTON_BORDER_WIDTH: f32 = 1.0;

/// How much of a surface an icon button brings with it.
#[derive(Copy, Clone, Debug, PartialEq, Eq, Default)]
pub enum IconButtonVariant {
    /// No surface at all: the glyph, and the ink a tap leaves.
    #[default]
    Standard,
    /// The accent, filled.
    Filled,
    /// A tonal fill.
    Tonal,
    /// An outline and no fill.
    Outlined,
}

/// What the button draws: one of the bundled icons, or a glyph of your own.
enum Content {
    Icon(IconData),
    Glyph(String),
    /// A pair being crossed, and the end it is heading for — see
    /// [`IconButton::animated`].
    Morph(crate::icons::AnimatedIconData, f32),
    /// A picture rather than a path — see [`IconButton::image`]. Boxed: a picture is
    /// several times the size of the other three, and every button would carry it.
    Image(Box<crate::ImageIcon>),
}

/// A button holding one glyph.
pub struct IconButton<Msg = crate::callback::Callback> {
    content: Content,
    variant: IconButtonVariant,
    selected: bool,
    enabled: bool,
    label: Option<String>,
    on_press: Option<Msg>,
    size: Option<f32>,
    icon_size: Option<f32>,
    color: Option<Color>,
    icon_color: Option<Color>,
    border_color: Option<Color>,
    border_width: Option<f32>,
    radius: Option<BorderRadius>,
    tap_target: Option<TapTarget>,
}

impl<Msg> IconButton<Msg> {
    /// A button showing one of the bundled icons.
    pub fn new(icon: IconData) -> Self {
        Self::of(Content::Icon(icon))
    }

    /// A button showing a **glyph** — an arrow, a cross, an ellipsis — for the many shapes
    /// the bundled set does not carry.
    pub fn glyph(glyph: impl Into<String>) -> Self {
        Self::of(Content::Glyph(glyph.into()))
    }

    /// A button showing a **picture**: a brand mark, a flag, a glyph that is artwork
    /// rather than a path.
    ///
    /// It is drawn at the button's own glyph size, like every other kind of mark here, so
    /// a picture and an icon in one bar are the same size without either being told.
    ///
    /// ```ignore
    /// IconButton::image(ImageIcon::new(Image::memory(MARK))).label("Home").on_press(msg)
    /// ```
    pub fn image(icon: crate::ImageIcon) -> Self {
        Self::of(Content::Image(Box::new(icon)))
    }

    /// **A button whose mark crosses between two**, at the end `on` names — a drawer's
    /// hamburger becoming a cross as the drawer opens, a play becoming a pause.
    ///
    /// The button does not time the crossing: it declares the end and the runtime drives
    /// the value there, the way a drawer's own slide is driven. Two controls reading the
    /// same flag are therefore at the same place on the same frame, because it is the
    /// same rule moving both and not two timers that happen to agree.
    ///
    /// ```
    /// use frus_widgets::{AnimatedIcons, IconButton};
    ///
    /// let drawer_open = false;
    /// let _button = IconButton::<()>::animated(AnimatedIcons::MENU_CLOSE, drawer_open)
    ///     .label("Menu")
    ///     .on_press(());
    /// ```
    pub fn animated(icon: crate::icons::AnimatedIconData, on: bool) -> Self {
        Self::of(Content::Morph(icon, if on { 1.0 } else { 0.0 }))
    }

    fn of(content: Content) -> Self {
        Self {
            content,
            variant: IconButtonVariant::default(),
            selected: false,
            enabled: true,
            label: None,
            on_press: None,
            size: None,
            icon_size: None,
            color: None,
            icon_color: None,
            border_color: None,
            border_width: None,
            radius: None,
            tap_target: None,
        }
    }

    /// What a screen reader announces. An icon has no text of its own, so without this the
    /// button is a shape with no name.
    pub fn label(mut self, label: impl Into<String>) -> Self {
        self.label = Some(label.into());
        self
    }

    /// Chooses how much surface the button brings.
    pub fn variant(mut self, variant: IconButtonVariant) -> Self {
        self.variant = variant;
        self
    }

    /// Marks it **on** — a toggle that is currently pressed in. The glyph takes the accent.
    pub fn selected(mut self, selected: bool) -> Self {
        self.selected = selected;
        self
    }

    /// Enables or disables it. Disabled, it is greyed out and emits nothing.
    pub fn enabled(mut self, enabled: bool) -> Self {
        self.enabled = enabled;
        self
    }

    /// The message emitted on click.
    pub fn on_press(mut self, message: impl Into<Msg>) -> Self {
        self.on_press = Some(message.into());
        self
    }

    /// The box's side.
    pub fn size(mut self, size: f32) -> Self {
        self.size = Some(size);
        self
    }

    /// The glyph's size inside it.
    pub fn icon_size(mut self, size: f32) -> Self {
        self.icon_size = Some(size);
        self
    }

    /// The surface under the glyph.
    pub fn color(mut self, color: Color) -> Self {
        self.color = Some(color);
        self
    }

    /// The glyph's colour.
    pub fn icon_color(mut self, color: Color) -> Self {
        self.icon_color = Some(color);
        self
    }

    /// The outline's colour.
    pub fn border_color(mut self, color: Color) -> Self {
        self.border_color = Some(color);
        self
    }

    /// The outline's thickness; `0.0` removes it.
    pub fn border_width(mut self, width: f32) -> Self {
        self.border_width = Some(width);
        self
    }

    /// The corner radii. Unset, the button is a **circle**.
    pub fn radius(mut self, radius: impl Into<BorderRadius>) -> Self {
        self.radius = Some(radius.into());
        self
    }

    /// **How much room it reserves for a finger** ([`TapTarget`]). Unset, the theme's
    /// answer, which is [`Padded`](TapTarget::Padded) — at least 48 pixels either way,
    /// whatever this control paints in the middle of it.
    pub fn tap_target(mut self, target: TapTarget) -> Self {
        self.tap_target = Some(target);
        self
    }

    fn side(&self, theme: &Theme) -> f32 {
        self.size
            .or(theme.widgets.icon_button.size)
            .unwrap_or(ICON_BUTTON_SIZE)
    }

    /// The room this button reserves, resolved as `caller ?? theme ?? framework`
    /// (`icon_button.dart:708`).
    fn reserved(&self, theme: &Theme) -> f32 {
        self.tap_target
            .or(theme.widgets.icon_button.tap_target)
            .unwrap_or(theme.tap_target)
            .min_side()
    }

    /// The **face** — what the button paints — centred in the box it was given, which is
    /// its tap target and is larger.
    fn face(&self, bounds: Rect, theme: &Theme) -> Rect {
        let side = self.side(theme);
        Rect::new(
            bounds.x + (bounds.width - side) * 0.5,
            bounds.y + (bounds.height - side) * 0.5,
            side,
            side,
        )
    }

    fn glyph_size(&self, theme: &Theme) -> f32 {
        self.icon_size
            .or(theme.widgets.icon_button.icon_size)
            .unwrap_or(ICON_BUTTON_ICON_SIZE)
    }

    fn radius_of(&self, theme: &Theme, side: f32) -> BorderRadius {
        self.radius
            .or(theme.widgets.icon_button.radius)
            // A circle, which is what an icon button is: the radius follows the box, so a
            // smaller one stays round instead of becoming a square with soft corners.
            .unwrap_or(BorderRadius::uniform(side / 2.0))
    }

    /// `(surface, glyph, outline)`.
    fn palette(&self, theme: &Theme) -> (Color, Color, Option<Color>) {
        if !self.enabled {
            return (
                match self.variant {
                    IconButtonVariant::Standard | IconButtonVariant::Outlined => Color::TRANSPARENT,
                    _ => disabled_container(theme),
                },
                disabled_content(theme),
                // An outlined icon button **keeps its outline**, at the container opacity.
                // Dropping it took the shape away entirely: milestone 324's golden showed a
                // disabled stepper as two bare glyphs with no buttons around them, which
                // reads as broken rather than as unavailable.
                match self.variant {
                    IconButtonVariant::Outlined => Some(disabled_container(theme)),
                    _ => None,
                },
            );
        }
        let (surface, glyph, outline) = match self.variant {
            IconButtonVariant::Standard => (
                Color::TRANSPARENT,
                if self.selected {
                    theme.scheme.primary
                } else {
                    theme.scheme.on_surface_variant
                },
                None,
            ),
            IconButtonVariant::Filled => (theme.scheme.primary, theme.scheme.on_primary, None),
            IconButtonVariant::Tonal => (
                theme.scheme.secondary_container,
                theme.scheme.on_secondary_container,
                None,
            ),
            IconButtonVariant::Outlined => (
                Color::TRANSPARENT,
                if self.selected {
                    theme.scheme.primary
                } else {
                    theme.scheme.on_surface_variant
                },
                Some(theme.scheme.outline),
            ),
        };
        (
            self.color
                .or(theme.widgets.icon_button.color)
                .unwrap_or(surface),
            self.icon_color
                .or(theme.widgets.icon_button.icon_color)
                .unwrap_or(glyph),
            self.border_color
                .or(theme.widgets.icon_button.border_color)
                .or(outline),
        )
    }
}

impl<Msg: Clone> Widget<Msg> for IconButton<Msg> {
    fn style(&self) -> Style {
        Widget::<Msg>::style_themed(self, &Theme::default())
    }

    /// **The box is the tap target, not the face** (`icon_button.dart:708`). An icon
    /// button paints 40 pixels and the reference reserves 48 for the finger, painting the
    /// face in the middle of it. This is the control most often placed at the very edge
    /// of a bar, where the eight missing pixels are the ones a thumb reaches for.
    fn style_themed(&self, theme: &Theme) -> Style {
        let side = self.side(theme).max(self.reserved(theme));
        Style {
            width: Dimension::Length(side),
            height: Dimension::Length(side),
            ..Default::default()
        }
    }

    fn children(&self) -> &[Box<dyn Widget<Msg>>] {
        &[]
    }

    fn paint(&self, bounds: Rect, status: Status, theme: &Theme, scene: &mut Scene) {
        let o = status.opacity;
        let (surface, glyph, outline) = self.palette(theme);
        let bounds = self.face(bounds, theme);
        let radius = self.radius_of(theme, bounds.height.min(bounds.width));
        let (border_width, border_color) = match (
            self.border_width.or(theme.widgets.icon_button.border_width),
            outline,
        ) {
            (Some(width), Some(color)) => (width, color),
            (Some(width), None) => (width, theme.scheme.outline),
            (None, Some(color)) => (ICON_BUTTON_BORDER_WIDTH, color),
            (None, None) => (0.0, Color::TRANSPARENT),
        };
        let surface = if self.enabled {
            theme.state_layer(surface, glyph, &status)
        } else {
            surface
        };
        scene.draw_rect(
            bounds,
            surface.fade(o),
            radius,
            border_width,
            border_color.fade(o),
        );

        let size = self.glyph_size(theme);
        match &self.content {
            // The end of the animation is what an isolated frame draws — a test, a
            // golden, the frame before the loop has advanced anything — which is the
            // same rule `Status::value` already applies on mount.
            Content::Morph(pair, _) => {
                let path = pair.at(status.value).placed(
                    size,
                    bounds.x + (bounds.width - size) / 2.0,
                    bounds.y + (bounds.height - size) / 2.0,
                    theme.direction,
                );
                scene.fill_path(&path, glyph.fade(o));
            }
            Content::Icon(name) => {
                let path = name.placed(
                    size,
                    bounds.x + (bounds.width - size) / 2.0,
                    bounds.y + (bounds.height - size) / 2.0,
                    theme.direction,
                );
                scene.fill_path(&path, glyph.fade(o));
            }
            // The picture takes the button's glyph size, which is what makes a mark drawn
            // from a bitmap and one drawn from a path interchangeable in a row of actions.
            Content::Image(icon) => {
                let square = Rect::new(
                    bounds.x + (bounds.width - size) / 2.0,
                    bounds.y + (bounds.height - size) / 2.0,
                    size,
                    size,
                );
                icon.paint_at(square, status, theme, scene);
            }
            Content::Glyph(text) => {
                let style = TextStyle::new(size);
                let measured = frus_text::measure_styled(
                    text,
                    size,
                    style.resolved().weight,
                    style.resolved().italic,
                );
                scene.text(
                    Point::new(
                        bounds.x + (bounds.width - measured.width) / 2.0,
                        bounds.y + (bounds.height - measured.height) / 2.0,
                    ),
                    text.clone(),
                    &style.resolved(),
                    glyph.fade(o),
                );
            }
        }
    }

    /// Only a morphing button has an animated value; every other one answers `None` and
    /// keeps the behaviour it had before this existed.
    fn anim_target(&self) -> Option<f32> {
        match self.content {
            Content::Morph(_, target) => Some(target),
            _ => None,
        }
    }

    fn on_click(&self) -> Option<Msg> {
        if self.enabled {
            self.on_press.clone()
        } else {
            None
        }
    }

    fn ink(&self, theme: &Theme) -> Option<crate::InkStyle> {
        if !self.enabled {
            return None;
        }
        let (_, glyph, _) = self.palette(theme);
        let splash = theme.widgets.ink.color.unwrap_or_else(|| glyph.fade(0.16));
        Some(
            crate::InkStyle::of(theme)
                .color(splash)
                .radius(self.radius_of(theme, self.side(theme))),
        )
    }

    fn focusable(&self) -> bool {
        self.enabled
    }

    fn semantics(&self) -> Option<frus_core::SemanticsProperties> {
        let semantics = frus_core::SemanticsProperties::new(frus_core::Role::Button);
        let semantics = match &self.label {
            Some(label) => semantics.label(label.clone()),
            // Better than nothing, and visibly worse than a label: a glyph read out is at
            // least something, an unnamed icon is silence.
            None => match &self.content {
                Content::Glyph(text) => semantics.label(text.clone()),
                Content::Icon(_) | Content::Morph(..) | Content::Image(_) => semantics,
            },
        };
        Some(if self.enabled {
            semantics.toggled(self.selected).clickable()
        } else {
            semantics.disabled(true)
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::icons::Icons;
    use crate::theme::{MIN_TAP_TARGET, SHRUNK_TAP_TARGET};
    use frus_core::Primitive;

    #[derive(Clone, Debug, PartialEq)]
    enum Msg {
        Pressed,
    }

    fn painted(button: &IconButton<Msg>) -> Vec<Primitive> {
        let mut scene = Scene::new();
        Widget::<Msg>::paint(
            button,
            Rect::new(0.0, 0.0, ICON_BUTTON_SIZE, ICON_BUTTON_SIZE),
            Status::default(),
            &Theme::default(),
            &mut scene,
        );
        scene.primitives().to_vec()
    }

    /// **A morphing button is a path, and it follows the animated value.** The mark it
    /// draws at half the crossing is neither end, and the button still says what it is
    /// for through its label rather than through the mark — a shape that is halfway
    /// between two things names neither of them.
    #[test]
    fn a_morphing_button_draws_the_crossing_and_still_says_what_it_does() {
        let paint_at = |value: f32| {
            let mut scene = Scene::new();
            Widget::<Msg>::paint(
                &IconButton::animated(crate::AnimatedIcons::MENU_CLOSE, true)
                    .label("Menu")
                    .on_press(Msg::Pressed),
                Rect::new(0.0, 0.0, ICON_BUTTON_SIZE, ICON_BUTTON_SIZE),
                Status {
                    value,
                    ..Status::default()
                },
                &Theme::default(),
                &mut scene,
            );
            scene
                .primitives()
                .iter()
                .find_map(|p| match p {
                    Primitive::Path { path, .. } => Some(path.clone()),
                    _ => None,
                })
                .expect("a morphing button paints a path")
        };
        assert_ne!(paint_at(0.0).verbs(), paint_at(0.5).verbs());
        assert_ne!(paint_at(0.5).verbs(), paint_at(1.0).verbs());

        let button = IconButton::animated(crate::AnimatedIcons::MENU_CLOSE, false)
            .label("Menu")
            .on_press(Msg::Pressed);
        assert_eq!(Widget::<Msg>::anim_target(&button), Some(0.0));
        assert_eq!(
            Widget::<Msg>::anim_target(&IconButton::<Msg>::new(Icons::CLOSE)),
            None,
            "a button that is one mark has no animated value"
        );
    }

    /// **An icon button paints 40 pixels and the reference reserves 48** (milestone 442,
    /// `icon_button.dart:708`). It is the control most often put at the very edge of a
    /// bar, where the eight missing pixels are the ones a thumb reaches for.
    #[test]
    fn an_icon_button_reserves_room_for_a_finger() {
        let theme = Theme::dark();
        let side = |button: &IconButton<()>, theme: &Theme| match Widget::<()>::style_themed(
            button, theme,
        )
        .width
        {
            Dimension::Length(w) => w,
            other => panic!("{other:?}"),
        };
        assert_eq!(side(&IconButton::new(Icons::CLOSE), &theme), MIN_TAP_TARGET);
        assert_eq!(
            side(
                &IconButton::new(Icons::CLOSE).tap_target(TapTarget::ShrinkWrap),
                &theme
            ),
            SHRUNK_TAP_TARGET
        );
        // A button asked for a face **larger** than the target keeps its own size: the
        // target is a floor, not a size.
        assert_eq!(
            side(&IconButton::new(Icons::CLOSE).size(64.0), &theme),
            64.0
        );
    }

    /// And **the face it paints does not grow with the room**: it keeps its own side and
    /// sits in the middle of it.
    #[test]
    fn the_face_is_centred_in_the_room() {
        let theme = Theme::dark();
        let mut scene = Scene::new();
        Widget::<()>::paint(
            &IconButton::new(Icons::CLOSE),
            Rect::new(0.0, 0.0, MIN_TAP_TARGET, MIN_TAP_TARGET),
            Status::default(),
            &theme,
            &mut scene,
        );
        let face = scene
            .primitives()
            .iter()
            .find_map(|p| match p {
                frus_core::Primitive::Rect { rect, .. } => Some(*rect),
                _ => None,
            })
            .expect("an icon button paints its surface");
        assert_eq!(face.width, ICON_BUTTON_SIZE);
        assert_eq!(face.height, ICON_BUTTON_SIZE);
        let inset = (MIN_TAP_TARGET - ICON_BUTTON_SIZE) * 0.5;
        assert!(
            (face.x - inset).abs() < 0.01 && (face.y - inset).abs() < 0.01,
            "centred in the room: {face:?}"
        );
    }

    #[test]
    fn it_is_a_circle_as_wide_as_it_is_tall() {
        let theme = Theme::default();
        // The **box** is square at the tap target since milestone 442; the face it paints
        // inside that box is square at its own side.
        let style = Widget::<Msg>::style_themed(&IconButton::new(Icons::CLOSE), &theme);
        assert_eq!(style.width, Dimension::Length(MIN_TAP_TARGET));
        assert_eq!(style.height, Dimension::Length(MIN_TAP_TARGET));
        let radius = painted(&IconButton::new(Icons::CLOSE))
            .iter()
            .find_map(|p| match p {
                Primitive::Rect { radius, .. } => Some(*radius),
                _ => None,
            })
            .expect("a box");
        assert_eq!(radius, BorderRadius::uniform(ICON_BUTTON_SIZE / 2.0));
    }

    #[test]
    fn a_standard_one_is_a_glyph_and_nothing_else() {
        let theme = Theme::default();
        let painted = painted(&IconButton::new(Icons::CLOSE));
        let (color, border) = painted
            .iter()
            .find_map(|p| match p {
                Primitive::Rect {
                    color,
                    border_width,
                    ..
                } => Some((*color, *border_width)),
                _ => None,
            })
            .expect("a box");
        assert_eq!(color, Color::TRANSPARENT, "no surface at rest");
        assert_eq!(border, 0.0);
        let glyph = painted
            .iter()
            .find_map(|p| match p {
                Primitive::Path { fill, .. } => *fill,
                _ => None,
            })
            .expect("an icon");
        assert_eq!(glyph, theme.scheme.on_surface_variant);
    }

    #[test]
    fn a_glyph_is_drawn_where_the_set_has_no_icon() {
        // The bundled set has no back arrow, no minus, no ellipsis. A button that only took
        // what happens to be bundled would send those call sites back to `Button`.
        let painted = painted(&IconButton::<Msg>::glyph("\u{2190}"));
        assert!(
            painted
                .iter()
                .any(|p| matches!(p, Primitive::Text { text, .. } if text == "\u{2190}")),
            "the glyph is drawn"
        );
    }

    #[test]
    fn selected_takes_the_accent() {
        let theme = Theme::default();
        let glyph = |selected: bool| {
            painted(&IconButton::<Msg>::new(Icons::STAR).selected(selected))
                .iter()
                .find_map(|p| match p {
                    Primitive::Path { fill, .. } => *fill,
                    _ => None,
                })
                .expect("an icon")
        };
        assert_eq!(glyph(false), theme.scheme.on_surface_variant);
        assert_eq!(glyph(true), theme.scheme.primary);
    }

    #[test]
    fn the_variants_are_told_apart_by_their_surface() {
        let theme = Theme::default();
        let surface = |variant: IconButtonVariant| {
            painted(&IconButton::<Msg>::new(Icons::CLOSE).variant(variant))
                .iter()
                .find_map(|p| match p {
                    Primitive::Rect {
                        color,
                        border_width,
                        ..
                    } => Some((*color, *border_width)),
                    _ => None,
                })
                .expect("a box")
        };
        assert_eq!(surface(IconButtonVariant::Filled).0, theme.scheme.primary);
        assert_eq!(
            surface(IconButtonVariant::Tonal).0,
            theme.scheme.secondary_container
        );
        let outlined = surface(IconButtonVariant::Outlined);
        assert_eq!(outlined.0, Color::TRANSPARENT);
        assert_eq!(outlined.1, ICON_BUTTON_BORDER_WIDTH);
    }

    #[test]
    fn disabled_is_inert_and_says_so() {
        let button = IconButton::new(Icons::CLOSE)
            .on_press(Msg::Pressed)
            .enabled(false);
        assert_eq!(Widget::on_click(&button), None);
        assert!(!Widget::<Msg>::focusable(&button));
        assert!(Widget::<Msg>::ink(&button, &Theme::default()).is_none());
        let semantics = Widget::<Msg>::semantics(&button).expect("semantics");
        assert!(semantics.disabled);
        assert!(!semantics.clickable);
    }

    #[test]
    fn an_icon_button_can_be_named() {
        // An icon says nothing to a screen reader; the label is what it is announced by.
        let named = IconButton::<Msg>::new(Icons::CLOSE).label("Remove");
        assert_eq!(
            Widget::<Msg>::semantics(&named).unwrap().label.as_deref(),
            Some("Remove")
        );
        // A glyph at least reads as itself.
        assert_eq!(
            Widget::<Msg>::semantics(&IconButton::<Msg>::glyph("+"))
                .unwrap()
                .label
                .as_deref(),
            Some("+")
        );
    }

    #[test]
    fn every_measurement_is_the_callers_and_then_the_themes() {
        let mut theme = Theme::default();
        theme.widgets.icon_button.size = Some(56.0);
        // The **face** — what the button paints — since milestone 442, because the box
        // around it is the tap target and is a floor rather than a size.
        let side = |button: IconButton<Msg>, theme: &Theme| {
            let mut scene = Scene::new();
            Widget::<Msg>::paint(
                &button,
                Rect::new(0.0, 0.0, 96.0, 96.0),
                Status::default(),
                theme,
                &mut scene,
            );
            scene
                .primitives()
                .iter()
                .find_map(|p| match p {
                    Primitive::Rect { rect, .. } => Some(rect.width),
                    _ => None,
                })
                .expect("a box")
        };
        assert_eq!(
            side(IconButton::new(Icons::CLOSE), &Theme::default()),
            ICON_BUTTON_SIZE,
            "the framework's"
        );
        assert_eq!(
            side(IconButton::new(Icons::CLOSE), &theme),
            56.0,
            "the theme's"
        );
        assert_eq!(
            side(IconButton::new(Icons::CLOSE).size(32.0), &theme),
            32.0,
            "the caller's, over the theme's"
        );
        // And a face smaller than the target still gets the target's room around it: the
        // control shrinks, the area a finger may land in does not.
        assert_eq!(
            match Widget::<Msg>::style_themed(&IconButton::new(Icons::CLOSE).size(32.0), &theme)
                .width
            {
                Dimension::Length(w) => w,
                other => panic!("{other:?}"),
            },
            MIN_TAP_TARGET
        );
    }
}