oxframe_2d/

handles.rs

use std::ops::Deref;

use kurbo::{BezPath, Point};
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};

use oxframe_core::{BlendMode, Color, Ease, Gradient, Seconds, Signal, Tween, Vec2, all};

use crate::builder::{
    self, CameraBuilder, CircleBuilder, CodeBuilder, GridBuilder, GroupBuilder, ImgBuilder,
    LayoutBuilder, LineBuilder, NodeBuilder, ParticlesBuilder, PathBuilder, PolygonBuilder,
    RectBuilder, ShaderBuilder, StarBuilder, SvgBuilder, TxtBuilder,
};
use crate::draw::{LineCap, LineJoin};
use crate::graph::{NodeId, NodeKind, SceneGraph, with_graph};
use crate::place::{Edge, Place, SafeArea, Side};
use crate::text::RichSpan;

/// How far [`Node::slide_in`] starts from the node's place, in pixels.
pub const SLIDE_DISTANCE: f64 = 160.0;

/// Untyped node handle with the properties every node has.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct Node(NodeId);

macro_rules! base_signal {
    ($($(#[$doc:meta])* $field:ident: $ty:ty),* $(,)?) => {
        $(
            $(#[$doc])*
            #[doc = ""]
            #[doc = concat!("The `", stringify!($field), "` property as an animatable signal.")]
            pub fn $field(self) -> Signal<$ty> {
                with_graph(|g| g.node(self.0).$field.clone())
            }
        )*
    };
}

impl Node {
    /// Index of the node in the scene graph.
    pub fn id(self) -> NodeId {
        self.0
    }

    /// Wraps an id from [`NodeBuilder::build`](crate::NodeBuilder::build).
    ///
    /// Other crates implement [`NodeBuilder`](crate::NodeBuilder) with this:
    /// the `parent` argument is only an id, and handles are what `add` needs.
    pub fn from_id(id: NodeId) -> Self {
        Self(id)
    }

    base_signal! {
        x: f64,
        y: f64,
        /// Degrees, clockwise.
        rotation: f64,
        scale: Vec2,
        opacity: f64,
        fill: Color,
        stroke: Color,
        line_width: f64,
        /// Start of the drawn part of the outline (fraction of its length).
        start: f64,
        /// End of the drawn part of the outline.
        end: f64,
        fill_gradient: Option<Gradient>,
        stroke_gradient: Option<Gradient>,
        dash: Vec<f64>,
        dash_offset: f64,
        line_cap: LineCap,
        line_join: LineJoin,
        blur: f64,
        shadow_color: Color,
        shadow_blur: f64,
        shadow_offset: Vec2,
        clip: bool,
        blend: BlendMode,
        z_index: f64,
        anchor: Vec2,
        grow: f64,
        shrink: f64,
        basis: Option<f64>,
        margin: f64,
        align_self: Option<crate::LayoutAlign>,
    }

    /// Adds a child node; children are positioned relative to the parent.
    ///
    /// The call site is stored on the node (`oxframe check` and `oxframe
    /// inspect` print it). `.name("title")` overrides the automatic label.
    #[allow(clippy::should_implement_trait)] // `view.add(..)` mirrors Motion Canvas
    #[track_caller]
    pub fn add<B: NodeBuilder>(self, child: B) -> B::Handle {
        let loc = std::panic::Location::caller();
        let prev = crate::graph::push_add_at(loc.file(), loc.line());
        let handle = builder::add(self.0, child);
        crate::graph::pop_add_at(prev);
        handle
    }

    /// Detaches the node from its parent; it stops being drawn.
    pub fn remove(self) {
        with_graph(|g| g.detach(self.0));
    }

    /// Fades the node in from transparent, over the theme's normal duration
    /// with its enter easing.
    pub fn fade_in(self) -> Tween<f64> {
        let motion = crate::theme::current().motion;
        self.opacity().set(0.0);
        self.opacity().to(1.0, motion.normal).ease(motion.enter)
    }

    /// Grows the node from nothing to its current scale with a small
    /// overshoot (the theme's emphasis easing, `OUT_BACK` by default).
    pub fn pop_in(self) -> Tween<Vec2> {
        let motion = crate::theme::current().motion;
        let full = self.scale().peek();
        self.scale().set(Vec2::ZERO);
        self.scale().to(full, motion.normal).ease(motion.emphasis)
    }

    /// Draws the outline from start to end (`end` from 0 to 1), as if with a
    /// pen. Works on every shape with an outline: paths, lines, rectangles,
    /// circles, polygons.
    pub fn draw_on(self) -> Tween<f64> {
        let motion = crate::theme::current().motion;
        self.end().set(0.0);
        self.end().to(1.0, motion.slow).ease(motion.enter)
    }

    /// Slides the node into its place from `SLIDE_DISTANCE` pixels towards
    /// `from`, fading in on the way.
    pub fn slide_in(self, from: Side) -> impl std::future::Future<Output = ()> + 'static {
        let motion = crate::theme::current().motion;
        let (axis, offset) = match from {
            Side::Left => (self.x(), -SLIDE_DISTANCE),
            Side::Right => (self.x(), SLIDE_DISTANCE),
            Side::Top => (self.y(), -SLIDE_DISTANCE),
            Side::Bottom => (self.y(), SLIDE_DISTANCE),
        };
        let home = axis.peek();
        axis.set(home + offset);
        let moves = all((
            axis.to(home, motion.normal).ease(motion.enter),
            self.fade_in(),
        ));
        async move {
            moves.await;
        }
    }

    /// Sits just outside `other`. The gap is the theme's `Md` step, and the
    /// position is recomputed every frame.
    pub fn next_to(self, other: impl Into<Node>, side: Side) -> Self {
        let other = other.into();
        with_graph(|g| g.set_place(self.0, Place::next_to(other.id(), side)));
        self
    }

    /// Lines this node's `edge` up with the same edge of `other`.
    pub fn align_to(self, other: impl Into<Node>, edge: Edge) -> Self {
        let other = other.into();
        with_graph(|g| g.set_place(self.0, Place::align_to(other.id(), edge)));
        self
    }

    /// Pins one edge to the safe area. The other axis is left as it is.
    pub fn to_edge(self, edge: Edge) -> Self {
        with_graph(|g| g.set_place(self.0, Place::to_edge(edge)));
        self
    }

    /// Same center as `other`.
    pub fn center_in(self, other: impl Into<Node>) -> Self {
        let other = other.into();
        with_graph(|g| g.set_place(self.0, Place::center_in(other.id())));
        self
    }

    /// Fades the node out, over the theme's normal duration with its exit easing.
    pub fn fade_out(self) -> Tween<f64> {
        let motion = crate::theme::current().motion;
        self.opacity().to(0.0, motion.normal).ease(motion.exit)
    }

    /// Moves the node under another parent.
    pub fn reparent(self, parent: impl Into<Node>) {
        let parent = parent.into();
        with_graph(|g| g.reparent(self.0, parent.0));
    }

    /// Direct children, in creation order.
    pub fn children(self) -> Vec<Node> {
        with_graph(|g| g.node(self.0).children.iter().map(|&c| Node(c)).collect())
    }

    /// Size of the node's box in its own coordinates.
    pub fn size(self) -> (f64, f64) {
        with_graph(|g| g.measure(self.0))
    }

    /// Position of the node's origin in scene coordinates.
    pub fn absolute_position(self) -> Vec2 {
        with_graph(|g| (g.world_transform(self.0).unwrap_or_default() * Point::ZERO).to_vec2())
    }
}

macro_rules! typed_handle {
    ($name:ident, $builder:ident) => {
        #[doc = concat!("Handle to a `", stringify!($name), "` node in the scene: cheap to copy, its")]
        #[doc = "methods return the node's properties as [`Signal`]s. Derefs to [`Node`]."]
        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
        pub struct $name(Node);

        impl $name {
            /// Starts a builder; add it with [`Node::add`] (e.g. `view.add(..)`).
            #[allow(clippy::new_ret_no_self)]
            pub fn new() -> $builder {
                $builder::default()
            }

            pub(crate) fn from_id(id: NodeId) -> Self {
                Self(Node(id))
            }

            /// The untyped node handle (same as `*self`).
            pub fn node(self) -> Node {
                self.0
            }
        }

        impl Deref for $name {
            type Target = Node;
            fn deref(&self) -> &Node {
                &self.0
            }
        }

        impl From<$name> for Node {
            fn from(h: $name) -> Node {
                h.0
            }
        }
    };
}

typed_handle!(Group, GroupBuilder);
typed_handle!(Camera, CameraBuilder);
typed_handle!(Rect, RectBuilder);
typed_handle!(Circle, CircleBuilder);
typed_handle!(Path, PathBuilder);
typed_handle!(Line, LineBuilder);
typed_handle!(Txt, TxtBuilder);
typed_handle!(Img, ImgBuilder);
typed_handle!(Svg, SvgBuilder);
typed_handle!(Layout, LayoutBuilder);
typed_handle!(Grid, GridBuilder);
typed_handle!(Polygon, PolygonBuilder);
typed_handle!(Star, StarBuilder);
typed_handle!(Code, CodeBuilder);

/// Handle to geometry drawn by a closure. Derefs to [`Node`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct Custom(Node);

impl Custom {
    /// Starts a builder. `draw` is called every time the frame is painted,
    /// with the frame time in seconds. It must depend only on that time, on
    /// signals it captured, and on `ctx.rng(seed)`.
    #[allow(clippy::new_ret_no_self)]
    pub fn new(draw: impl Fn(&mut crate::draw::DrawCtx, f64) + 'static) -> crate::CustomBuilder {
        crate::CustomBuilder::from_draw(draw)
    }

    pub(crate) fn from_id(id: NodeId) -> Self {
        Self(Node(id))
    }

    /// The untyped node handle.
    pub fn node(self) -> Node {
        self.0
    }
}

impl Deref for Custom {
    type Target = Node;
    fn deref(&self) -> &Node {
        &self.0
    }
}

/// Handle to a WGSL shader. Derefs to [`Node`].
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct Shader(Node);

impl Shader {
    /// A shader from WGSL text. The text defines `struct Params`, the
    /// uniform `p`, and `fn shade`. oxframe adds `ox` and `ShadeIn`.
    ///
    /// The waves preset is what gets painted. A custom `shade` is
    /// type-checked on every draw.
    #[allow(clippy::new_ret_no_self)]
    pub fn source(wgsl: impl Into<String>) -> ShaderBuilder {
        ShaderBuilder::new(crate::shader::ShaderCode::Wgsl(wgsl.into()))
    }

    /// A shader read from `path` on every draw, so saving the file updates
    /// the running scene without a rebuild.
    pub fn file(path: impl AsRef<std::path::Path>) -> ShaderBuilder {
        ShaderBuilder::new(crate::shader::ShaderCode::File(path.as_ref().into()))
    }

    pub(crate) fn from_id(id: NodeId) -> Self {
        Self(Node(id))
    }

    /// The untyped node handle.
    pub fn node(self) -> Node {
        self.0
    }

    /// The numeric uniform `name`.
    ///
    /// # Panics
    ///
    /// If the shader has no numeric uniform with that name. The message
    /// lists the names it does have.
    pub fn uniform(self, name: &str) -> Signal<f64> {
        self.number(name)
    }

    /// Wave height of the waves preset.
    pub fn amp(self) -> Signal<f64> {
        self.number("amp")
    }

    /// Crest speed of the waves preset.
    pub fn speed(self) -> Signal<f64> {
        self.number("speed")
    }

    /// Water color of the waves preset.
    pub fn deep(self) -> Signal<Color> {
        self.color("deep")
    }

    /// Crest color of the waves preset.
    pub fn foam(self) -> Signal<Color> {
        self.color("foam")
    }

    fn number(self, name: &str) -> Signal<f64> {
        with_graph(|g| {
            let NodeKind::Shader { uniforms, .. } = &g.node(self.id()).kind else {
                unreachable!("handle does not point to a Shader");
            };
            for u in uniforms {
                if u.name == name
                    && let crate::shader::UniformValue::Num(v) = &u.value
                {
                    return v.clone();
                }
            }
            panic!("no numeric uniform {name}. {}", uniform_names(uniforms));
        })
    }

    fn color(self, name: &str) -> Signal<Color> {
        with_graph(|g| {
            let NodeKind::Shader { uniforms, .. } = &g.node(self.id()).kind else {
                unreachable!("handle does not point to a Shader");
            };
            for u in uniforms {
                if u.name == name
                    && let crate::shader::UniformValue::Color(v) = &u.value
                {
                    return v.clone();
                }
            }
            panic!("no color uniform {name}. {}", uniform_names(uniforms));
        })
    }
}

fn uniform_names(uniforms: &[crate::shader::Uniform]) -> String {
    let names: Vec<&str> = uniforms.iter().map(|u| u.name.as_str()).collect();
    format!("Available: {}.", names.join(", "))
}

impl Deref for Shader {
    type Target = Node;
    fn deref(&self) -> &Node {
        &self.0
    }
}

impl From<Custom> for Node {
    fn from(h: Custom) -> Node {
        h.0
    }
}

typed_handle!(Particles, ParticlesBuilder);

macro_rules! kind_signal {
    ($handle:ident :: $kind:ident { $($(#[$doc:meta])* $field:ident: $ty:ty),* $(,)? }) => {
        impl $handle {
            $(
                $(#[$doc])*
                #[doc = ""]
                #[doc = concat!("The `", stringify!($field), "` property as an animatable signal.")]
                pub fn $field(self) -> Signal<$ty> {
                    with_graph(|g| match &g.node(self.id()).kind {
                        NodeKind::$kind { $field, .. } => $field.clone(),
                        _ => unreachable!(concat!("handle does not point to a ", stringify!($kind))),
                    })
                }
            )*
        }
    };
}

kind_signal!(Particles::Particles { gravity: f64 });

impl Particles {
    /// Emits `count` particles from `origin` at the current script time.
    ///
    /// The future is ready immediately: the burst is an event, and the
    /// particles then move on their own. Seeking back before this time
    /// removes them; seeking forward restores the same dots.
    pub fn burst(self, origin: impl Into<Vec2>, count: u32) -> oxframe_core::WaitFor {
        let origin = origin.into();
        let time = oxframe_core::time();
        with_graph(|g| {
            if let NodeKind::Particles { state, .. } = &g.node(self.id()).kind {
                state.bursts.borrow_mut().push(crate::sim::Burst {
                    time,
                    origin,
                    count,
                });
            }
        });
        oxframe_core::wait_for(0.0)
    }
}

kind_signal!(Rect::Rect {
    width: f64,
    height: f64,
    radius: f64
});
kind_signal!(Circle::Circle {
    /// Diameter.
    size: f64,
    start_angle: f64,
    end_angle: f64,
});
kind_signal!(Polygon::Polygon {
    sides: f64,
    size: f64
});
kind_signal!(Star::Star {
    points: f64,
    size: f64,
    inner: f64
});
kind_signal!(Path::Path { data: BezPath });
kind_signal!(Camera::Camera {
    /// 1 shows the world at its size, 2 twice as big.
    zoom: f64
});

impl Camera {
    /// Moves the camera so `node`'s center is in the middle of the frame.
    pub fn center_on(
        self,
        node: impl Into<Node>,
        duration: impl Seconds,
    ) -> impl std::future::Future<Output = ()> + 'static {
        let node = node.into();
        let d = duration.seconds();
        let target = with_graph(|g| g.box_in(node.id(), self.id())).map(|r| r.center());
        let moves = target.map(|c| all((self.x().to(c.x, d), self.y().to(c.y, d))));
        async move {
            if let Some(m) = moves {
                m.await;
            }
        }
    }

    /// Centers on `node` and zooms so all of it fits in the frame with
    /// `padding` pixels to spare. Measures the node when called, so a layout
    /// that is still growing fits at its current size.
    pub fn fit(
        self,
        node: impl Into<Node>,
        padding: f64,
        duration: impl Seconds,
    ) -> impl std::future::Future<Output = ()> + 'static {
        let node = node.into();
        let d = duration.seconds();
        let (bounds, (fw, fh)) = with_graph(|g| (g.box_in(node.id(), self.id()), g.frame_size()));
        let moves = bounds.map(|r| {
            let zoom = ((fw - 2.0 * padding) / r.width().max(1e-6))
                .min((fh - 2.0 * padding) / r.height().max(1e-6))
                .max(1e-3);
            let c = r.center();
            all((
                self.x().to(c.x, d),
                self.y().to(c.y, d),
                self.zoom().to(zoom, d),
            ))
        });
        async move {
            if let Some(m) = moves {
                m.await;
            }
        }
    }

    /// Back to the start: looking at the origin, no zoom, no rotation.
    pub fn reset(self, duration: impl Seconds) -> impl std::future::Future<Output = ()> + 'static {
        let d = duration.seconds();
        let moves = all((
            self.x().to(0.0, d),
            self.y().to(0.0, d),
            self.zoom().to(1.0, d),
            self.rotation().to(0.0, d),
        ));
        async move {
            moves.await;
        }
    }
}
kind_signal!(Line::Line { points: Vec<Vec2>, arrow_size: f64 });
kind_signal!(Txt::Txt { text: String, spans: Vec<RichSpan>, font_size: f64, weight: f64 });
kind_signal!(Code::Code {
    font_size: f64,
    /// Focused lines as (first, last), 1-based; (0, 0) = all.
    focus: Vec2,
    /// Alpha of unfocused lines.
    dim: f64,
});

impl Txt {
    /// Morphs to `text` glyph by glyph: letters present in both strings
    /// travel to their new places, the others fade.
    pub fn morph_to(self, text: impl Into<String>, duration: f64) -> oxframe_core::BoxFuture {
        let to = text.into();
        let (txt, morph, t) = with_graph(|g| match &g.node(self.id()).kind {
            NodeKind::Txt {
                text,
                morph,
                morph_t,
                ..
            } => (text.clone(), morph.clone(), morph_t.clone()),
            _ => unreachable!("handle does not point to a Txt"),
        });
        Box::pin(async move {
            morph.set(Some((txt.get(), to.clone())));
            t.set(0.0);
            t.to(1.0, duration).await;
            txt.set(to);
            morph.set(None);
        })
    }
}

impl Code {
    /// The source.
    ///
    /// `.to(next, seconds)` diffs the two versions: tokens that stay slide
    /// to their new places, deleted tokens fade and collapse, new tokens
    /// fade in. `Txt` types its text out; code does not. `.get()`, `.set()`
    /// and `.bind()` still replace the source with no animation, and `.set`
    /// cancels a diff that is already running.
    pub fn code(self) -> CodeText {
        with_graph(|g| match &g.node(self.id()).kind {
            NodeKind::Code {
                code,
                edit_from,
                edit_to,
                editing,
                edit_t,
                edit_flash,
                focus,
                lang,
                ..
            } => CodeText {
                code: code.clone(),
                edit_from: edit_from.clone(),
                edit_to: edit_to.clone(),
                editing: editing.clone(),
                edit_t: edit_t.clone(),
                edit_flash: edit_flash.clone(),
                focus: focus.clone(),
                lang: *lang,
            },
            _ => unreachable!("handle does not point to a Code"),
        })
    }

    /// Moves the focus to lines `first..=last` over `duration`.
    ///
    /// Lines are 1-based. While a diff is running, a focus that sits on
    /// lines which shift rides with those lines, and lands on their new
    /// numbers when the diff ends.
    pub fn focus_lines(
        self,
        first: usize,
        last: usize,
        duration: f64,
    ) -> oxframe_core::Tween<Vec2> {
        self.focus()
            .to(Vec2::new(first as f64, last as f64), duration)
    }

    /// Inserts `text` at `line` (1-based) and `col` (0-based characters).
    ///
    /// # Panics
    ///
    /// If the line or column is outside the current source. The line just
    /// after the last one, column 0, is the end of the source.
    pub fn insert(
        self,
        line: usize,
        col: usize,
        text: impl Into<String>,
        duration: impl Seconds,
    ) -> CodeTween {
        let text = text.into();
        let src = self.code().get();
        let next = oxframe_text::insert_at(&src, line, col, &text)
            .unwrap_or_else(|e| panic!("code.insert: {e}"));
        self.code().to(next, duration)
    }

    /// Removes the half-open range `((start_line, start_col), (end_line, end_col))`.
    ///
    /// Lines are 1-based, columns are 0-based characters. `((5, 0), (6, 0))`
    /// removes line 5.
    ///
    /// # Panics
    ///
    /// If a point is outside the source, or the end is before the start.
    pub fn remove(
        self,
        range: ((usize, usize), (usize, usize)),
        duration: impl Seconds,
    ) -> CodeTween {
        self.rewrite(range, String::new(), duration, "code.remove")
    }

    /// Replaces the half-open range with `text`. See [`remove`](Self::remove)
    /// for how the range is counted.
    ///
    /// # Panics
    ///
    /// If a point is outside the source, or the end is before the start.
    pub fn replace(
        self,
        range: ((usize, usize), (usize, usize)),
        text: impl Into<String>,
        duration: impl Seconds,
    ) -> CodeTween {
        self.rewrite(range, text.into(), duration, "code.replace")
    }

    fn rewrite(
        self,
        ((l0, c0), (l1, c1)): ((usize, usize), (usize, usize)),
        text: String,
        duration: impl Seconds,
        what: &str,
    ) -> CodeTween {
        let src = self.code().get();
        let next = oxframe_text::replace_range(
            &src,
            oxframe_text::Loc { line: l0, col: c0 },
            oxframe_text::Loc { line: l1, col: c1 },
            &text,
        )
        .unwrap_or_else(|e| panic!("{what}: {e}"));
        self.code().to(next, duration)
    }
}

/// The source of a [`Code`] node.
///
/// Dereferences to the underlying [`Signal`], so `.get()` reads it.
/// [`.to()`](CodeText::to) runs a diff tween instead of the typewriter
/// [`Signal::to`](Signal::to) uses for plain strings.
#[derive(Clone)]
pub struct CodeText {
    code: Signal<String>,
    edit_from: Signal<String>,
    edit_to: Signal<String>,
    editing: Signal<bool>,
    edit_t: Signal<f64>,
    edit_flash: Signal<bool>,
    focus: Signal<Vec2>,
    lang: oxframe_text::Lang,
}

impl std::ops::Deref for CodeText {
    type Target = Signal<String>;
    fn deref(&self) -> &Signal<String> {
        &self.code
    }
}

impl CodeText {
    /// Replaces the source immediately and cancels a running diff.
    pub fn set(&self, value: impl Into<String>) {
        self.editing.set(false);
        self.code.set(value.into());
    }

    /// Makes the source follow `f`, and cancels a running diff.
    pub fn bind(&self, f: impl Fn() -> String + 'static) {
        self.editing.set(false);
        self.code.bind(f);
    }

    /// Diffs the current source into `target` over `duration`.
    pub fn to(&self, target: impl Into<String>, duration: impl Seconds) -> CodeTween {
        let target = target.into();
        let from = self.code.get();
        self.edit_from.set(from.clone());
        self.edit_to.set(target.clone());
        self.edit_flash.set(false);
        self.editing.set(true);
        self.edit_t.set(0.0);
        CodeTween {
            tween: self.edit_t.to(1.0, duration),
            code: self.code.clone(),
            editing: self.editing.clone(),
            edit_flash: self.edit_flash.clone(),
            focus: self.focus.clone(),
            lang: self.lang,
            from,
            target,
            finished: false,
        }
    }
}

/// Diff tween returned by [`CodeText::to`], [`Code::insert`], [`Code::remove`]
/// and [`Code::replace`].
#[must_use = "a tween does nothing unless awaited"]
pub struct CodeTween {
    tween: Tween<f64>,
    code: Signal<String>,
    editing: Signal<bool>,
    edit_flash: Signal<bool>,
    focus: Signal<Vec2>,
    lang: oxframe_text::Lang,
    from: String,
    target: String,
    finished: bool,
}

impl CodeTween {
    /// Easing curve. The default is [`presets::DEFAULT`](oxframe_core::presets::DEFAULT).
    pub fn ease(mut self, ease: impl Ease + 'static) -> Self {
        self.tween = self.tween.ease(ease);
        self
    }

    /// Changes the length. `f64` is seconds; a theme pace is a duration too.
    pub fn duration(mut self, duration: impl Seconds) -> Self {
        self.tween = self.tween.duration(duration);
        self
    }

    /// Flashes a background behind text that this edit inserts.
    pub fn flash(self) -> Self {
        self.edit_flash.set(true);
        self
    }
}

impl Future for CodeTween {
    type Output = ();

    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
        let this = self.get_mut();
        if Pin::new(&mut this.tween).poll(cx).is_pending() {
            return Poll::Pending;
        }
        if !this.finished {
            this.finished = true;
            let focus = this.focus.get();
            let (a, b) = (focus.x.round() as i64, focus.y.round() as i64);
            if a > 0 || b > 0 {
                let diff = oxframe_text::diff_code(&this.from, &this.target, this.lang);
                if let Some((n0, n1)) =
                    oxframe_text::map_focus(&diff, a.max(0) as usize, b.max(0) as usize)
                {
                    this.focus.set(Vec2::new(n0 as f64, n1 as f64));
                }
            }
            this.code.set(this.target.clone());
            this.editing.set(false);
        }
        Poll::Ready(())
    }
}
kind_signal!(Svg::Svg {
    width: f64,
    height: f64
});

impl Svg {
    /// The node imported from the SVG element with this `id`.
    ///
    /// # Panics
    ///
    /// If the file has no element with that id.
    pub fn find(self, id: &str) -> Node {
        let id = with_graph(|g| g.descendant_named(self.id(), id))
            .unwrap_or_else(|| panic!("svg has no element with id {id:?}"));
        Node::from_id(id)
    }

    /// Every path from the file, in paint order.
    pub fn paths(self) -> Vec<Path> {
        with_graph(|g| {
            g.descendant_paths(self.id())
                .into_iter()
                .map(Path::from_id)
                .collect()
        })
    }
}

kind_signal!(Img::Img {
    width: f64,
    height: f64
});
kind_signal!(Layout::Layout {
    gap: f64,
    padding: f64,
    radius: f64,
    /// Fixed width; `None` sizes to content.
    width: Option<f64>,
    /// Fixed height; `None` sizes to content.
    height: Option<f64>,
});
kind_signal!(Grid::Grid {
    width: f64,
    height: f64,
    spacing: f64
});

/// Root of a scene. Origin is the center of the frame, y points down.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct View(Node);

impl View {
    /// The view of the scene being executed.
    pub fn current() -> Self {
        Self(Node(SceneGraph::ROOT))
    }

    /// Frame size in pixels.
    pub fn size(self) -> (u32, u32) {
        with_graph(|g| g.size())
    }

    /// True when the frame is taller than it is wide.
    pub fn is_portrait(self) -> bool {
        let (w, h) = self.size();
        h > w
    }

    /// The rectangle [`Node::to_edge`](crate::Node::to_edge) pins to, in scene
    /// coordinates. A portrait frame leaves room for a vertical video's
    /// status bar and buttons.
    pub fn safe_area(self) -> SafeArea {
        let (w, h) = self.size();
        SafeArea::for_frame(f64::from(w), f64::from(h))
    }
}

impl Deref for View {
    type Target = Node;
    fn deref(&self) -> &Node {
        &self.0
    }
}

impl From<View> for Node {
    fn from(v: View) -> Node {
        v.0
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::Primitive;

    fn scene(f: impl FnOnce(View)) -> std::rc::Rc<SceneGraph> {
        let graph = SceneGraph::new(400, 400);
        graph.enter(|| f(View::current()));
        graph
    }

    /// Runs `scene` to the end inside a graph; returns the frames it took.
    fn play(
        scene_fn: impl FnOnce(View) -> std::pin::Pin<Box<dyn std::future::Future<Output = ()>>>,
    ) -> u32 {
        let graph = SceneGraph::new(400, 400);
        graph.enter(|| {
            let fut = scene_fn(View::current());
            let mut ex =
                oxframe_core::Executor::new(60.0, oxframe_protocol::Meta::default(), 0, fut);
            let mut frames = 0;
            while !ex.step() {
                frames += 1;
                assert!(frames < 10_000, "scene did not finish");
            }
            frames
        })
    }

    /// Screen position of a node's origin.
    fn screen(n: impl Into<Node>) -> (f64, f64) {
        let p = n.into().absolute_position();
        ((p.x * 1e6).round() / 1e6, (p.y * 1e6).round() / 1e6)
    }

    #[test]
    fn camera_pans_zooms_and_turns_its_children_only() {
        scene(|view| {
            let cam = view.add(Camera::new());
            let dot = cam.add(Circle::new().size(10.0).x(100.0).y(50.0));
            let hud = view.add(Txt::new().text("HUD").x(-300.0).y(-200.0));
            // A fresh camera changes nothing.
            assert_eq!(screen(dot), (100.0, 50.0));
            // Looking at the dot brings it to the center.
            cam.x().set(100.0);
            cam.y().set(50.0);
            assert_eq!(screen(dot), (0.0, 0.0));
            // Zoom scales distances from the point looked at.
            cam.zoom().set(2.0);
            let other = cam.add(Circle::new().size(10.0).x(110.0).y(50.0));
            assert_eq!(screen(other), (20.0, 0.0));
            // Turning the camera clockwise turns the world the other way.
            cam.rotation().set(90.0);
            assert_eq!(screen(other), (0.0, -20.0));
            // Nodes outside the camera stay put.
            assert_eq!(screen(hud), (-300.0, -200.0));
        });
    }

    #[test]
    fn camera_center_on_fit_and_reset() {
        play(|view| {
            let cam = view.add(Camera::new());
            let card = cam.add(Rect::new().width(200.0).height(100.0).x(300.0).y(-100.0));
            let row = cam.add(
                Layout::new()
                    .x(-500.0)
                    .gap(10.0)
                    .child(Rect::new().size(50.0))
                    .child(Rect::new().size(50.0)),
            );
            Box::pin(async move {
                cam.center_on(card, 1.0).await;
                assert_eq!((cam.x().get(), cam.y().get()), (300.0, -100.0));
                assert_eq!(screen(card), (0.0, 0.0));
                // 400×400 frame, 20 px padding: limited by width (360 / 200).
                cam.fit(card, 20.0, 0.0).await;
                assert!(
                    (cam.zoom().get() - 1.8).abs() < 1e-9,
                    "{}",
                    cam.zoom().get()
                );
                // A layout that grew is fitted at its current size.
                row.gap().to(110.0, 0.5).await;
                cam.fit(row, 0.0, 0.0).await;
                let (w, _) = row.size();
                assert!((w - 210.0).abs() < 1e-6, "layout width {w}");
                assert!((cam.zoom().get() - 400.0 / 210.0).abs() < 1e-9);
                assert!((cam.x().get() + 500.0).abs() < 1e-9);
                cam.reset(0.5).await;
                assert_eq!(
                    (
                        cam.x().get(),
                        cam.y().get(),
                        cam.zoom().get(),
                        cam.rotation().get()
                    ),
                    (0.0, 0.0, 1.0, 0.0)
                );
            })
        });
    }

    #[test]
    fn entrance_helpers_start_at_once_and_end_in_place() {
        let normal = crate::theme::current().motion.normal;
        let expected = (normal * 60.0).round() as u32;
        let frames = play(|view| {
            let r = view.add(Rect::new().size(100.0).x(50.0));
            let pop = r.pop_in();
            // The start value is set when the helper is called, not awaited:
            // nothing flashes in its final state for a frame.
            assert_eq!(r.scale().get(), Vec2::ZERO);
            let slide = r.slide_in(Side::Left);
            assert_eq!(r.x().get(), 50.0 - SLIDE_DISTANCE);
            assert_eq!(r.opacity().get(), 0.0);
            let draw = r.draw_on();
            assert_eq!(r.end().get(), 0.0);
            Box::pin(async move {
                all((pop, slide)).await;
                assert_eq!(r.scale().get(), Vec2::new(1.0, 1.0));
                assert_eq!((r.x().get(), r.opacity().get()), (50.0, 1.0));
                draw.await;
                assert_eq!(r.end().get(), 1.0);
                r.fade_out().duration(0.5).await;
                assert_eq!(r.opacity().get(), 0.0);
            })
        });
        let slow = crate::theme::current().motion.slow;
        assert_eq!(frames, expected + (slow * 60.0).round() as u32 + 30);
    }

    #[test]
    fn a_diff_lands_on_the_new_source_and_moves_the_focus() {
        play(|view| {
            let code = view.add(Code::new().code("a\nkeep\n").focus(2, 2));
            Box::pin(async move {
                code.insert(1, 0, "NEW\n", 0.2).flash().await;
                assert_eq!(code.code().get(), "NEW\na\nkeep\n");
                let f = code.focus().get();
                assert_eq!((f.x.round() as i32, f.y.round() as i32), (3, 3));
                code.replace(((3, 0), (3, 4)), "stay", 0.0).await;
                assert_eq!(code.code().get(), "NEW\na\nstay\n");
            })
        });
    }

    #[test]
    fn add_records_its_call_site_and_scene_bounds() {
        let g = scene(|view| {
            view.add(Rect::new().size(100.0).name("box"));
            view.add(Rect::new().size(10.0).x(100.0));
        });
        let nodes = g.inspect_nodes();
        let named = nodes.iter().find(|n| n.name == "box").unwrap();
        assert_eq!(named.kind, "Rect");
        assert!(named.source.as_ref().unwrap().contains("handles.rs:"));
        assert!(
            (named.bounds[0] + 50.0).abs() < 1e-6 && (named.bounds[2] - 50.0).abs() < 1e-6,
            "{:?}",
            named.bounds
        );
        let auto = nodes
            .iter()
            .find(|n| n.name != "box" && n.name != "view")
            .unwrap();
        assert_eq!(auto.name, auto.source.clone().unwrap());
    }

    #[test]
    fn builders_set_initial_values_and_handles_return_signals() {
        scene(|view| {
            let r = view.add(
                Rect::new()
                    .size(50.0)
                    .radius(5.0)
                    .x(-10.0)
                    .fill(Color::BLACK),
            );
            assert_eq!(r.width().get(), 50.0);
            assert_eq!(r.height().get(), 50.0);
            assert_eq!(r.radius().get(), 5.0);
            assert_eq!(r.x().get(), -10.0);
            assert_eq!(r.fill().get(), Color::BLACK);
            r.x().set(3.0);
            assert_eq!(r.x().get(), 3.0);
            let c = r.add(Circle::new().size(10.0));
            assert_eq!(r.children(), vec![c.node()]);
            assert_eq!(view.children(), vec![r.node()]);
            assert_eq!(c.size().name().as_deref(), Some("Circle#2.size"));
        });
    }

    #[test]
    fn draw_list_composes_transforms() {
        let g = scene(|view| {
            let grp = view.add(Group::new().x(10.0).scale(2.0));
            grp.add(Circle::new().x(5.0));
        });
        let items = g.draw_list();
        assert_eq!(items.len(), 1);
        assert_eq!(items[0].transform * Point::ZERO, Point::new(20.0, 0.0));
    }

    #[test]
    fn layout_places_children_in_a_row() {
        let g = scene(|view| {
            view.add(
                Layout::new()
                    .gap(10.0)
                    .padding(5.0)
                    .child(Rect::new().size(20.0))
                    .child(Rect::new().width(40.0).height(10.0)),
            );
        });
        let layout = NodeId(1);
        assert_eq!(g.measure(layout), (5.0 + 20.0 + 10.0 + 40.0 + 5.0, 30.0));
        let centers: Vec<_> = g
            .draw_list()
            .iter()
            .map(|i| i.transform * Point::ZERO)
            .collect();
        // Total 80 wide: first box spans -35..-15, second -5..35.
        assert_eq!(centers, vec![Point::new(-25.0, 0.0), Point::new(15.0, 0.0)]);
    }

    #[test]
    fn column_with_fixed_size_and_alignment() {
        let g = scene(|view| {
            view.add(
                Layout::new()
                    .column()
                    .height(100.0)
                    .width(100.0)
                    .justify(crate::Justify::Start)
                    .align(crate::LayoutAlign::Start)
                    .child(Rect::new().size(20.0)),
            );
        });
        let c = g.draw_list()[0].transform * Point::ZERO;
        assert_eq!(c, Point::new(-40.0, -40.0));
    }

    #[test]
    fn text_line_path_and_img_draw() {
        let png = {
            let mut v = Vec::new();
            image::RgbaImage::from_pixel(4, 2, image::Rgba([255, 0, 0, 255]))
                .write_to(&mut std::io::Cursor::new(&mut v), image::ImageFormat::Png)
                .unwrap();
            v
        };
        let g = scene(|view| {
            let t = view.add(Txt::new().text("Hi").font_size(40.0));
            assert!(t.size().0 > 20.0);
            view.add(
                Line::new()
                    .points([(0.0, 0.0), (100.0, 0.0)])
                    .end_arrow(true),
            );
            view.add(Path::new().svg("M0 0 L10 0 L10 10 Z"));
            let img = view.add(Img::new().src(&png).width(40.0));
            assert_eq!(img.height().get(), 20.0);
        });
        let kinds: Vec<_> = g
            .draw_list()
            .iter()
            .map(|i| match i.prim {
                Primitive::Fill { .. } => "fill",
                Primitive::Stroke { .. } => "stroke",
                Primitive::Image { .. } => "image",
                Primitive::PushLayer(_) => "push",
                Primitive::PopLayer => "pop",
            })
            .collect();
        assert_eq!(kinds, vec!["fill", "stroke", "fill", "fill", "image"]);
    }

    #[test]
    fn trimming_and_pick() {
        let g = scene(|view| {
            view.add(Rect::new().size(100.0).name("back"));
            view.add(Circle::new().size(40.0).x(30.0).end(0.5));
        });
        assert_eq!(g.pick(Point::new(-40.0, 0.0)), Some(NodeId(1)));
        assert_eq!(g.pick(Point::new(300.0, 0.0)), None);
        // The half circle covers the right half of its disc.
        assert_eq!(g.pick(Point::new(45.0, 0.0)), Some(NodeId(2)));
    }

    fn kinds(g: &SceneGraph) -> Vec<&'static str> {
        g.draw_list()
            .iter()
            .map(|i| match i.prim {
                Primitive::Fill { .. } => "fill",
                Primitive::Stroke { .. } => "stroke",
                Primitive::Image { .. } => "image",
                Primitive::PushLayer(_) => "push",
                Primitive::PopLayer => "pop",
            })
            .collect()
    }

    #[test]
    fn layers_only_when_needed_and_balanced() {
        // Translucent leaf: opacity folds into the paint, no layer.
        let g = scene(|v| {
            v.add(Rect::new().opacity(0.5));
        });
        assert_eq!(kinds(&g), ["fill"]);
        // Translucent group with children: one layer around them.
        let g = scene(|v| {
            v.add(
                Group::new()
                    .opacity(0.5)
                    .child(Rect::new())
                    .child(Circle::new()),
            );
        });
        assert_eq!(kinds(&g), ["push", "fill", "fill", "pop"]);
        // Clip wraps only the children; shadow wraps node + children.
        let g = scene(|v| {
            v.add(
                Circle::new()
                    .clip(true)
                    .shadow(Color::BLACK, 4.0, (2.0, 2.0))
                    .child(Rect::new()),
            );
        });
        assert_eq!(kinds(&g), ["push", "fill", "push", "fill", "pop", "pop"]);
    }

    #[test]
    fn z_index_orders_siblings_and_anchor_moves_box() {
        let g = scene(|v| {
            v.add(Rect::new().name("a").z_index(2.0));
            v.add(Rect::new().name("b"));
            v.add(Rect::new().name("c").size(20.0).anchor((-1.0, -1.0)).x(5.0));
        });
        let items = g.draw_list();
        let order: Vec<u32> = items.iter().map(|i| i.node.0).collect();
        assert_eq!(order, vec![2, 3, 1]);
        // Anchored at the top-left: the box center sits at (5+10, 0+10).
        assert_eq!(items[1].transform * Point::ZERO, Point::new(15.0, 10.0));
    }

    fn boxes(g: &SceneGraph) -> Vec<(Point, f64)> {
        g.draw_list()
            .iter()
            .filter_map(|i| match &i.prim {
                Primitive::Fill { path, .. } => {
                    let bb = kurbo::Shape::bounding_box(path);
                    Some((i.transform * Point::ZERO, bb.width()))
                }
                _ => None,
            })
            .collect()
    }

    #[test]
    fn flex_grow_stretch_wrap_and_grid() {
        use crate::{Justify, LayoutAlign};
        // grow: a 200-wide row; the second child takes the free space.
        let g = scene(|v| {
            v.add(
                Layout::new()
                    .width(200.0)
                    .justify(Justify::Start)
                    .child(Rect::new().size(40.0))
                    .child(Rect::new().size(40.0).grow(1.0)),
            );
        });
        let b = boxes(&g);
        assert_eq!(b[0], (Point::new(-80.0, 0.0), 40.0));
        assert_eq!(b[1], (Point::new(20.0, 0.0), 160.0));

        // stretch: children fill the cross axis.
        let g = scene(|v| {
            v.add(
                Layout::new()
                    .column()
                    .width(120.0)
                    .align(LayoutAlign::Stretch)
                    .child(Rect::new().size(30.0)),
            );
        });
        assert_eq!(boxes(&g)[0].1, 120.0);

        // wrap: three 60-wide boxes in 130 → two lines.
        let g = scene(|v| {
            v.add(
                Layout::new()
                    .width(130.0)
                    .wrap(true)
                    .child(Rect::new().size(60.0))
                    .child(Rect::new().size(60.0))
                    .child(Rect::new().size(60.0)),
            );
        });
        let ys: Vec<f64> = boxes(&g).iter().map(|b| b.0.y).collect();
        assert_eq!(ys[0], ys[1]);
        assert!(ys[2] > ys[0]);

        // grid: 2 columns of equal width.
        let g = scene(|v| {
            v.add(
                Layout::new()
                    .grid(2)
                    .width(200.0)
                    .align(LayoutAlign::Stretch)
                    .child(Rect::new().size(10.0))
                    .child(Rect::new().size(10.0))
                    .child(Rect::new().size(10.0)),
            );
        });
        let b = boxes(&g);
        assert_eq!(
            b.iter().map(|b| b.1).collect::<Vec<_>>(),
            vec![100.0, 100.0, 100.0]
        );
        assert_eq!(b[2].0.x, b[0].0.x);
        assert!(b[2].0.y > b[0].0.y);
    }

    #[test]
    fn describe_lists_signals() {
        let g = scene(|view| {
            view.add(Txt::new().text("abc"));
        });
        let d = g.describe(NodeId(1));
        assert!(d.iter().any(|(k, v)| k == "text" && v == "abc"));
    }
}