gpui_core/

taffy.rs

use crate::{
    AbsoluteLength, App, Bounds, DefiniteLength, Edges, GridTemplate, Length, Pixels, Point, Size,
    Style, Window, point, size,
    util::{
        ceil_to_device_pixel, round_half_toward_zero, round_stroke_to_device_pixel,
        round_to_device_pixel,
    },
};
use collections::{FxHashMap, FxHashSet};
use smallvec::SmallVec;
use stacksafe::{StackSafe, stacksafe};
use std::{fmt::Debug, ops::Range};
use taffy::{
    TaffyTree, TraversePartialTree as _,
    geometry::{Point as TaffyPoint, Rect as TaffyRect, Size as TaffySize},
    prelude::{max_content, min_content},
    style::AvailableSpace as TaffyAvailableSpace,
    tree::{LayoutInput, NodeId},
};

type NodeMeasureFn = StackSafe<
    Box<
        dyn FnMut(
            Size<Option<Pixels>>,
            Size<AvailableSpace>,
            &mut Window,
            &mut App,
        ) -> Size<Pixels>,
    >,
>;

struct NodeContext {
    measure: NodeMeasureFn,
}
pub struct TaffyLayoutEngine {
    taffy: TaffyTree<NodeContext>,
    absolute_layout_bounds: FxHashMap<LayoutId, Bounds<Pixels>>,
    absolute_outer_origins: FxHashMap<LayoutId, Point<f32>>,
    computed_layouts: FxHashSet<LayoutId>,
}

const EXPECT_MESSAGE: &str = "we should avoid taffy layout errors by construction if possible";

impl TaffyLayoutEngine {
    pub fn new() -> Self {
        let mut taffy = TaffyTree::new();
        taffy.disable_rounding();
        TaffyLayoutEngine {
            taffy,
            absolute_layout_bounds: FxHashMap::default(),
            absolute_outer_origins: FxHashMap::default(),
            computed_layouts: FxHashSet::default(),
        }
    }

    pub fn clear(&mut self) {
        self.taffy.clear();
        self.absolute_layout_bounds.clear();
        self.absolute_outer_origins.clear();
        self.computed_layouts.clear();
    }

    pub fn request_layout(
        &mut self,
        style: Style,
        rem_size: Pixels,
        scale_factor: f32,
        children: &[LayoutId],
    ) -> LayoutId {
        let taffy_style = style.to_taffy(rem_size, scale_factor);

        if children.is_empty() {
            self.taffy
                .new_leaf(taffy_style)
                .expect(EXPECT_MESSAGE)
                .into()
        } else {
            self.taffy
                // This is safe because LayoutId is repr(transparent) to taffy::tree::NodeId.
                .new_with_children(taffy_style, unsafe {
                    std::mem::transmute::<&[LayoutId], &[taffy::NodeId]>(children)
                })
                .expect(EXPECT_MESSAGE)
                .into()
        }
    }

    pub fn request_measured_layout(
        &mut self,
        style: Style,
        rem_size: Pixels,
        scale_factor: f32,
        measure: impl FnMut(
            Size<Option<Pixels>>,
            Size<AvailableSpace>,
            &mut Window,
            &mut App,
        ) -> Size<Pixels>
        + 'static,
    ) -> LayoutId {
        let taffy_style = style.to_taffy(rem_size, scale_factor);

        self.taffy
            .new_leaf_with_context(
                taffy_style,
                NodeContext {
                    measure: StackSafe::new(Box::new(measure)),
                },
            )
            .expect(EXPECT_MESSAGE)
            .into()
    }

    /// Treats auto dimensions of a root node as filling the viewport while
    /// preserving dimensions explicitly supplied by the element.
    pub fn stretch_auto_size_to_fill(
        &mut self,
        id: LayoutId,
        size: Size<Pixels>,
        scale_factor: f32,
    ) {
        let style = self.taffy.style(id.0).expect(EXPECT_MESSAGE);
        let stretch_width = style.size.width.is_auto();
        let stretch_height = style.size.height.is_auto();
        if !stretch_width && !stretch_height {
            return;
        }

        let mut style = style.clone();
        if stretch_width {
            style.size.width =
                taffy::style::Dimension::length(round_to_device_pixel(size.width.0, scale_factor));
        }
        if stretch_height {
            style.size.height =
                taffy::style::Dimension::length(round_to_device_pixel(size.height.0, scale_factor));
        }
        self.taffy.set_style(id.0, style).expect(EXPECT_MESSAGE);
    }

    // Used to understand performance
    #[allow(dead_code)]
    fn count_all_children(&self, parent: LayoutId) -> anyhow::Result<u32> {
        let mut count = 0;

        for child in self.taffy.children(parent.0)? {
            // Count this child.
            count += 1;

            // Count all of this child's children.
            count += self.count_all_children(LayoutId(child))?
        }

        Ok(count)
    }

    // Used to understand performance
    #[allow(dead_code)]
    fn max_depth(&self, depth: u32, parent: LayoutId) -> anyhow::Result<u32> {
        println!(
            "{parent:?} at depth {depth} has {} children",
            self.taffy.child_count(parent.0)
        );

        let mut max_child_depth = 0;

        for child in self.taffy.children(parent.0)? {
            max_child_depth = std::cmp::max(max_child_depth, self.max_depth(0, LayoutId(child))?);
        }

        Ok(depth + 1 + max_child_depth)
    }

    // Used to understand performance
    #[allow(dead_code)]
    fn get_edges(&self, parent: LayoutId) -> anyhow::Result<Vec<(LayoutId, LayoutId)>> {
        let mut edges = Vec::new();

        for child in self.taffy.children(parent.0)? {
            edges.push((parent, LayoutId(child)));

            edges.extend(self.get_edges(LayoutId(child))?);
        }

        Ok(edges)
    }

    #[stacksafe]
    pub fn compute_layout(
        &mut self,
        id: LayoutId,
        available_space: Size<AvailableSpace>,
        window: &mut Window,
        cx: &mut App,
    ) {
        // Leaving this here until we have a better instrumentation approach.
        // println!("Laying out {} children", self.count_all_children(id)?);
        // println!("Max layout depth: {}", self.max_depth(0, id)?);

        // Output the edges (branches) of the tree in Mermaid format for visualization.
        // println!("Edges:");
        // for (a, b) in self.get_edges(id)? {
        //     println!("N{} --> N{}", u64::from(a), u64::from(b));
        // }
        //

        if !self.computed_layouts.insert(id) {
            let mut stack = SmallVec::<[LayoutId; 64]>::new();
            stack.push(id);
            while let Some(id) = stack.pop() {
                self.absolute_layout_bounds.remove(&id);
                self.absolute_outer_origins.remove(&id);
                stack.extend(
                    self.taffy
                        .children(id.into())
                        .expect(EXPECT_MESSAGE)
                        .into_iter()
                        .map(Into::into),
                );
            }
        }

        let scale_factor = window.scale_factor();

        let transform = |v: AvailableSpace| match v {
            AvailableSpace::Definite(pixels) => {
                AvailableSpace::Definite(Pixels(pixels.0 * scale_factor))
            }
            AvailableSpace::MinContent => AvailableSpace::MinContent,
            AvailableSpace::MaxContent => AvailableSpace::MaxContent,
        };
        let available_space = size(
            transform(available_space.width),
            transform(available_space.height),
        );

        self.taffy
            .compute_layout_with_measure(
                id.into(),
                available_space.into(),
                |inputs: LayoutInput, _id, node_context, style| {
                    taffy::compute_leaf_layout(
                        inputs,
                        style,
                        |_, _| 0.0,
                        |known_dimensions, available_space| {
                            let Some(node_context) = node_context else {
                                return TaffySize::ZERO;
                            };

                            let known_dimensions = Size {
                                width: known_dimensions.width.map(|e| Pixels(e / scale_factor)),
                                height: known_dimensions.height.map(|e| Pixels(e / scale_factor)),
                            };

                            let available_space: Size<AvailableSpace> = available_space.into();
                            let untransform = |ev: AvailableSpace| match ev {
                                AvailableSpace::Definite(pixels) => {
                                    AvailableSpace::Definite(Pixels(pixels.0 / scale_factor))
                                }
                                AvailableSpace::MinContent => AvailableSpace::MinContent,
                                AvailableSpace::MaxContent => AvailableSpace::MaxContent,
                            };
                            let available_space = size(
                                untransform(available_space.width),
                                untransform(available_space.height),
                            );

                            let measured_size: Size<Pixels> = (node_context.measure)(
                                known_dimensions,
                                available_space,
                                window,
                                cx,
                            );
                            snap_measured_size_to_device_pixels(measured_size, scale_factor).into()
                        },
                    )
                },
            )
            .expect(EXPECT_MESSAGE);
    }

    // Pixel snapping converts layout coordinates into integer device-pixel
    // coordinates so painted edges land on physical pixel boundaries. Absolute
    // edge snapping preserves closure for coincident layout edges; pre-layout
    // metric snapping keeps fixed lengths such as borders and gaps stable.
    pub fn layout_bounds(&mut self, id: LayoutId, scale_factor: f32) -> Bounds<Pixels> {
        if let Some(layout) = self.absolute_layout_bounds.get(&id).cloned() {
            return layout;
        }

        let layout = self.taffy.layout(id.into()).expect(EXPECT_MESSAGE);
        let layout_location = layout.location;
        let layout_size = layout.size;
        let parent = self.taffy.parent(id.0);

        let absolute_outer_origin = match parent {
            Some(parent_id) => {
                let parent_id = LayoutId::from(parent_id);
                self.layout_bounds(parent_id, scale_factor);
                let parent_origin = *self
                    .absolute_outer_origins
                    .get(&parent_id)
                    .expect("parent absolute outer origin should be cached");
                parent_origin + Point::from(layout_location)
            }
            None => Point::from(layout_location),
        };
        self.absolute_outer_origins
            .insert(id, absolute_outer_origin);

        let layout_size = Size::from(layout_size);
        let absolute_far = absolute_outer_origin + point(layout_size.width, layout_size.height);
        let snapped_bounds = Bounds::from_corners(
            absolute_outer_origin.map(round_half_toward_zero),
            absolute_far.map(round_half_toward_zero),
        );

        let bounds = (snapped_bounds / scale_factor).map(Pixels);
        self.absolute_layout_bounds.insert(id, bounds);

        bounds
    }
}

/// A unique identifier for a layout node, generated when requesting a layout from Taffy
#[derive(Copy, Clone, Eq, PartialEq, Debug)]
#[repr(transparent)]
pub struct LayoutId(NodeId);

impl std::hash::Hash for LayoutId {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        u64::from(self.0).hash(state);
    }
}

impl From<NodeId> for LayoutId {
    fn from(node_id: NodeId) -> Self {
        Self(node_id)
    }
}

impl From<LayoutId> for NodeId {
    fn from(layout_id: LayoutId) -> NodeId {
        layout_id.0
    }
}

trait ToTaffy<Output> {
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> Output;
}

fn snap_measured_size_to_device_pixels(size: Size<Pixels>, scale_factor: f32) -> Size<f32> {
    size.map(|d| ceil_to_device_pixel(d.0.max(0.0), scale_factor))
}

fn border_widths_to_taffy(
    widths: &Edges<AbsoluteLength>,
    rem_size: Pixels,
    scale_factor: f32,
) -> TaffyRect<taffy::style::LengthPercentage> {
    let snap = |w: &AbsoluteLength| {
        taffy::style::LengthPercentage::length(round_stroke_to_device_pixel(
            w.to_pixels(rem_size).0,
            scale_factor,
        ))
    };
    TaffyRect {
        top: snap(&widths.top),
        right: snap(&widths.right),
        bottom: snap(&widths.bottom),
        left: snap(&widths.left),
    }
}

impl ToTaffy<taffy::style::Style> for Style {
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> taffy::style::Style {
        use taffy::style_helpers::{fr, length, minmax, repeat};

        fn to_grid_line(
            placement: &Range<crate::GridPlacement>,
        ) -> taffy::Line<taffy::GridPlacement> {
            taffy::Line {
                start: placement.start.into(),
                end: placement.end.into(),
            }
        }

        fn to_grid_repeat<T: taffy::style::CheapCloneStr>(
            unit: &Option<GridTemplate>,
        ) -> Vec<taffy::GridTemplateComponent<T>> {
            unit.map(|template| match template.min_size {
                crate::TemplateColumnMinSize::Zero => {
                    vec![repeat(
                        template.repeat,
                        vec![minmax(length(0.0_f32), fr(1.0_f32))],
                    )]
                }
                crate::TemplateColumnMinSize::MinContent => {
                    vec![repeat(
                        template.repeat,
                        vec![minmax(min_content(), fr(1.0_f32))],
                    )]
                }
                crate::TemplateColumnMinSize::MaxContent => {
                    vec![repeat(
                        template.repeat,
                        vec![minmax(length(0.0_f32), max_content())],
                    )]
                }
            })
            .unwrap_or_default()
        }

        taffy::style::Style {
            display: self.display.into(),
            overflow: self.overflow.into(),
            scrollbar_width: self.scrollbar_width.to_taffy(rem_size, scale_factor),
            position: self.position.into(),
            inset: self.inset.to_taffy(rem_size, scale_factor),
            size: self.size.to_taffy(rem_size, scale_factor),
            min_size: self.min_size.to_taffy(rem_size, scale_factor),
            max_size: self.max_size.to_taffy(rem_size, scale_factor),
            aspect_ratio: self.aspect_ratio,
            margin: self.margin.to_taffy(rem_size, scale_factor),
            padding: self.padding.to_taffy(rem_size, scale_factor),
            border: border_widths_to_taffy(&self.border_widths, rem_size, scale_factor),
            align_items: self.align_items.map(Into::into).unwrap_or_default(),
            align_self: self.align_self.map(|x| x.into()),
            align_content: self.align_content.map(Into::into).unwrap_or_default(),
            justify_content: self.justify_content.map(Into::into).unwrap_or_default(),
            gap: self.gap.to_taffy(rem_size, scale_factor),
            flex_direction: self.flex_direction.into(),
            flex_wrap: self.flex_wrap.into(),
            flex_basis: self.flex_basis.to_taffy(rem_size, scale_factor),
            flex_grow: self.flex_grow,
            flex_shrink: self.flex_shrink,
            grid_template_rows: to_grid_repeat(&self.grid_rows),
            grid_template_columns: to_grid_repeat(&self.grid_cols),
            grid_row: self
                .grid_location
                .as_ref()
                .map(|location| to_grid_line(&location.row))
                .unwrap_or_default(),
            grid_column: self
                .grid_location
                .as_ref()
                .map(|location| to_grid_line(&location.column))
                .unwrap_or_default(),
            ..Default::default()
        }
    }
}

impl ToTaffy<f32> for AbsoluteLength {
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> f32 {
        round_to_device_pixel(self.to_pixels(rem_size).0, scale_factor)
    }
}

impl ToTaffy<taffy::style::LengthPercentageAuto> for Length {
    fn to_taffy(
        &self,
        rem_size: Pixels,
        scale_factor: f32,
    ) -> taffy::prelude::LengthPercentageAuto {
        match self {
            Length::Definite(length) => length.to_taffy(rem_size, scale_factor),
            Length::Auto => taffy::prelude::LengthPercentageAuto::auto(),
        }
    }
}

impl ToTaffy<taffy::style::Dimension> for Length {
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> taffy::prelude::Dimension {
        match self {
            Length::Definite(length) => length.to_taffy(rem_size, scale_factor),
            Length::Auto => taffy::prelude::Dimension::auto(),
        }
    }
}

impl ToTaffy<taffy::style::LengthPercentage> for DefiniteLength {
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> taffy::style::LengthPercentage {
        match self {
            DefiniteLength::Absolute(length) => length.to_taffy(rem_size, scale_factor),
            DefiniteLength::Fraction(fraction) => {
                taffy::style::LengthPercentage::percent(*fraction)
            }
        }
    }
}

impl ToTaffy<taffy::style::LengthPercentageAuto> for DefiniteLength {
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> taffy::style::LengthPercentageAuto {
        match self {
            DefiniteLength::Absolute(length) => length.to_taffy(rem_size, scale_factor),
            DefiniteLength::Fraction(fraction) => {
                taffy::style::LengthPercentageAuto::percent(*fraction)
            }
        }
    }
}

impl ToTaffy<taffy::style::Dimension> for DefiniteLength {
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> taffy::style::Dimension {
        match self {
            DefiniteLength::Absolute(length) => length.to_taffy(rem_size, scale_factor),
            DefiniteLength::Fraction(fraction) => taffy::style::Dimension::percent(*fraction),
        }
    }
}

impl ToTaffy<taffy::style::LengthPercentage> for AbsoluteLength {
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> taffy::style::LengthPercentage {
        taffy::style::LengthPercentage::length(self.to_taffy(rem_size, scale_factor))
    }
}

impl ToTaffy<taffy::style::LengthPercentageAuto> for AbsoluteLength {
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> taffy::style::LengthPercentageAuto {
        taffy::style::LengthPercentageAuto::length(self.to_taffy(rem_size, scale_factor))
    }
}

impl ToTaffy<taffy::style::Dimension> for AbsoluteLength {
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> taffy::style::Dimension {
        taffy::style::Dimension::length(self.to_taffy(rem_size, scale_factor))
    }
}

impl<T, T2> From<TaffyPoint<T>> for Point<T2>
where
    T: Into<T2>,
    T2: Clone + Debug + Default + PartialEq,
{
    fn from(point: TaffyPoint<T>) -> Point<T2> {
        Point {
            x: point.x.into(),
            y: point.y.into(),
        }
    }
}

impl<T, T2> From<Point<T>> for TaffyPoint<T2>
where
    T: Into<T2> + Clone + Debug + Default + PartialEq,
{
    fn from(val: Point<T>) -> Self {
        TaffyPoint {
            x: val.x.into(),
            y: val.y.into(),
        }
    }
}

impl<T, U> ToTaffy<TaffySize<U>> for Size<T>
where
    T: ToTaffy<U> + Clone + Debug + Default + PartialEq,
{
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> TaffySize<U> {
        TaffySize {
            width: self.width.to_taffy(rem_size, scale_factor),
            height: self.height.to_taffy(rem_size, scale_factor),
        }
    }
}

impl<T, U> ToTaffy<TaffyRect<U>> for Edges<T>
where
    T: ToTaffy<U> + Clone + Debug + Default + PartialEq,
{
    fn to_taffy(&self, rem_size: Pixels, scale_factor: f32) -> TaffyRect<U> {
        TaffyRect {
            top: self.top.to_taffy(rem_size, scale_factor),
            right: self.right.to_taffy(rem_size, scale_factor),
            bottom: self.bottom.to_taffy(rem_size, scale_factor),
            left: self.left.to_taffy(rem_size, scale_factor),
        }
    }
}

impl<T, U> From<TaffySize<T>> for Size<U>
where
    T: Into<U>,
    U: Clone + Debug + Default + PartialEq,
{
    fn from(taffy_size: TaffySize<T>) -> Self {
        Size {
            width: taffy_size.width.into(),
            height: taffy_size.height.into(),
        }
    }
}

impl<T, U> From<Size<T>> for TaffySize<U>
where
    T: Into<U> + Clone + Debug + Default + PartialEq,
{
    fn from(size: Size<T>) -> Self {
        TaffySize {
            width: size.width.into(),
            height: size.height.into(),
        }
    }
}

/// The space available for an element to be laid out in
#[derive(Copy, Clone, Default, Debug, Eq, PartialEq)]
pub enum AvailableSpace {
    /// The amount of space available is the specified number of pixels
    Definite(Pixels),
    /// The amount of space available is indefinite and the node should be laid out under a min-content constraint
    #[default]
    MinContent,
    /// The amount of space available is indefinite and the node should be laid out under a max-content constraint
    MaxContent,
}

pub(crate) fn available_space_for_optional_width(width: Option<Pixels>) -> AvailableSpace {
    width.map_or(AvailableSpace::MaxContent, AvailableSpace::Definite)
}

impl AvailableSpace {
    /// Returns a `Size` with both width and height set to `AvailableSpace::MinContent`.
    ///
    /// This function is useful when you want to create a `Size` with the minimum content constraints
    /// for both dimensions.
    ///
    /// # Examples
    ///
    /// ```
    /// use gpui::AvailableSpace;
    /// let min_content_size = AvailableSpace::min_size();
    /// assert_eq!(min_content_size.width, AvailableSpace::MinContent);
    /// assert_eq!(min_content_size.height, AvailableSpace::MinContent);
    /// ```
    pub const fn min_size() -> Size<Self> {
        Size {
            width: Self::MinContent,
            height: Self::MinContent,
        }
    }
}

impl From<AvailableSpace> for TaffyAvailableSpace {
    fn from(space: AvailableSpace) -> TaffyAvailableSpace {
        match space {
            AvailableSpace::Definite(Pixels(value)) => TaffyAvailableSpace::Definite(value),
            AvailableSpace::MinContent => TaffyAvailableSpace::MinContent,
            AvailableSpace::MaxContent => TaffyAvailableSpace::MaxContent,
        }
    }
}

impl From<TaffyAvailableSpace> for AvailableSpace {
    fn from(space: TaffyAvailableSpace) -> AvailableSpace {
        match space {
            TaffyAvailableSpace::Definite(value) => AvailableSpace::Definite(Pixels(value)),
            TaffyAvailableSpace::MinContent => AvailableSpace::MinContent,
            TaffyAvailableSpace::MaxContent => AvailableSpace::MaxContent,
        }
    }
}

impl From<Pixels> for AvailableSpace {
    fn from(pixels: Pixels) -> Self {
        AvailableSpace::Definite(pixels)
    }
}

impl From<Size<Pixels>> for Size<AvailableSpace> {
    fn from(size: Size<Pixels>) -> Self {
        Size {
            width: AvailableSpace::Definite(size.width),
            height: AvailableSpace::Definite(size.height),
        }
    }
}

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

    #[test]
    fn optional_width_uses_max_content_when_unbounded() {
        assert_eq!(
            available_space_for_optional_width(None),
            AvailableSpace::MaxContent
        );
        assert_eq!(
            available_space_for_optional_width(Some(px(320.0))),
            AvailableSpace::Definite(px(320.0))
        );
    }
}