Switch back to custom geometry types, unified with layout primitives 🏞

1 files changed, 505 insertions, 0 deletions

diff --git a/src/layout/par.rs b/src/layout/par.rs
new file mode 100644
index 00000000..2a139760
--- /dev/null
+++ b/src/layout/par.rs
@@ -0,0 +1,505 @@
+use super::*;
+
+/// A node that arranges its children into a paragraph.
+///
+/// Boxes are laid out along the cross axis as long as they fit into a line.
+/// When necessary, a line break is inserted and the new line is offset along
+/// the main axis by the height of the previous line plus extra line spacing.
+#[derive(Debug, Clone, PartialEq)]
+pub struct Par {
+    pub dirs: Gen<Dir>,
+    pub line_spacing: Length,
+    pub children: Vec<LayoutNode>,
+    pub aligns: Gen<Align>,
+    pub expand: Spec<bool>,
+}
+
+#[async_trait(?Send)]
+impl Layout for Par {
+    async fn layout(
+        &self,
+        ctx: &mut LayoutContext,
+        constraints: LayoutConstraints,
+    ) -> Vec<LayoutItem> {
+        let mut layouter = LineLayouter::new(LineContext {
+            dirs: self.dirs,
+            spaces: constraints.spaces,
+            repeat: constraints.repeat,
+            line_spacing: self.line_spacing,
+            expand: self.expand,
+        });
+
+        for child in &self.children {
+            let items = child
+                .layout(ctx, LayoutConstraints {
+                    spaces: layouter.remaining(),
+                    repeat: constraints.repeat,
+                })
+                .await;
+
+            for item in items {
+                match item {
+                    LayoutItem::Spacing(amount) => layouter.push_spacing(amount),
+                    LayoutItem::Box(boxed, aligns) => layouter.push_box(boxed, aligns),
+                }
+            }
+        }
+
+        layouter
+            .finish()
+            .into_iter()
+            .map(|boxed| LayoutItem::Box(boxed, self.aligns))
+            .collect()
+    }
+}
+
+impl From<Par> for LayoutNode {
+    fn from(par: Par) -> Self {
+        Self::dynamic(par)
+    }
+}
+
+/// Performs the line layouting.
+struct LineLayouter {
+    /// The context used for line layouting.
+    ctx: LineContext,
+    /// The underlying layouter that stacks the finished lines.
+    stack: StackLayouter,
+    /// The in-progress line.
+    run: LineRun,
+}
+
+/// The context for line layouting.
+#[derive(Debug, Clone)]
+struct LineContext {
+    /// The layout directions.
+    dirs: Gen<Dir>,
+    /// The spaces to layout into.
+    spaces: Vec<LayoutSpace>,
+    /// Whether to spill over into copies of the last space or finish layouting
+    /// when the last space is used up.
+    repeat: bool,
+    /// The spacing to be inserted between each pair of lines.
+    line_spacing: Length,
+    /// Whether to expand the size of the resulting layout to the full size of
+    /// this space or to shrink it to fit the content.
+    expand: Spec<bool>,
+}
+
+impl LineLayouter {
+    /// Create a new line layouter.
+    fn new(ctx: LineContext) -> Self {
+        Self {
+            stack: StackLayouter::new(StackContext {
+                spaces: ctx.spaces.clone(),
+                dirs: ctx.dirs,
+                repeat: ctx.repeat,
+                expand: ctx.expand,
+            }),
+            ctx,
+            run: LineRun::new(),
+        }
+    }
+
+    /// Add a layout.
+    fn push_box(&mut self, layout: BoxLayout, aligns: Gen<Align>) {
+        let dirs = self.ctx.dirs;
+        if let Some(prev) = self.run.aligns {
+            if aligns.main != prev.main {
+                // TODO: Issue warning for non-fitting alignment in
+                // non-repeating context.
+                let fitting = aligns.main >= self.stack.space.allowed_align;
+                if !fitting && self.ctx.repeat {
+                    self.finish_space(true);
+                } else {
+                    self.finish_line();
+                }
+            } else if aligns.cross < prev.cross {
+                self.finish_line();
+            } else if aligns.cross > prev.cross {
+                let usable = self.stack.usable().get(dirs.cross.axis());
+
+                let mut rest_run = LineRun::new();
+                rest_run.size.main = self.run.size.main;
+
+                // FIXME: Alignment in non-expanding parent.
+                rest_run.usable = Some(match aligns.cross {
+                    Align::Start => unreachable!("start > x"),
+                    Align::Center => usable - 2.0 * self.run.size.cross,
+                    Align::End => usable - self.run.size.cross,
+                });
+
+                self.finish_line();
+
+                // Move back up in the stack layouter.
+                self.stack.push_spacing(-rest_run.size.main - self.ctx.line_spacing);
+                self.run = rest_run;
+            }
+        }
+
+        let size = layout.size.switch(dirs);
+        let usable = self.usable();
+
+        if usable.main < size.main || usable.cross < size.cross {
+            if !self.line_is_empty() {
+                self.finish_line();
+            }
+
+            // TODO: Issue warning about overflow if there is overflow.
+            let usable = self.usable();
+            if usable.main < size.main || usable.cross < size.cross {
+                self.stack.skip_to_fitting_space(layout.size);
+            }
+        }
+
+        self.run.aligns = Some(aligns);
+        self.run.layouts.push((self.run.size.cross, layout));
+
+        self.run.size.cross += size.cross;
+        self.run.size.main = self.run.size.main.max(size.main);
+    }
+
+    /// Add spacing to the line.
+    fn push_spacing(&mut self, mut spacing: Length) {
+        spacing = spacing.min(self.usable().cross);
+        self.run.size.cross += spacing;
+    }
+
+    /// The remaining usable size of the line.
+    ///
+    /// This specifies how much more would fit before a line break would be
+    /// needed.
+    fn usable(&self) -> Gen<Length> {
+        // The base is the usable space of the stack layouter.
+        let mut usable = self.stack.usable().switch(self.ctx.dirs);
+
+        // If there was another run already, override the stack's size.
+        if let Some(cross) = self.run.usable {
+            usable.cross = cross;
+        }
+
+        usable.cross -= self.run.size.cross;
+        usable
+    }
+
+    /// The remaining inner spaces. If something is laid out into these spaces,
+    /// it will fit into this layouter's underlying stack.
+    fn remaining(&self) -> Vec<LayoutSpace> {
+        let mut spaces = self.stack.remaining();
+        *spaces[0].size.get_mut(self.ctx.dirs.main.axis()) -= self.run.size.main;
+        spaces
+    }
+
+    /// Whether the currently set line is empty.
+    fn line_is_empty(&self) -> bool {
+        self.run.size == Gen::ZERO && self.run.layouts.is_empty()
+    }
+
+    /// Finish everything up and return the final collection of boxes.
+    fn finish(mut self) -> Vec<BoxLayout> {
+        self.finish_line_if_not_empty();
+        self.stack.finish()
+    }
+
+    /// Finish the active space and start a new one.
+    ///
+    /// At the top level, this is a page break.
+    fn finish_space(&mut self, hard: bool) {
+        self.finish_line_if_not_empty();
+        self.stack.finish_space(hard)
+    }
+
+    /// Finish the active line and start a new one.
+    fn finish_line(&mut self) {
+        let dirs = self.ctx.dirs;
+
+        let mut layout = BoxLayout::new(self.run.size.switch(dirs).to_size());
+        let aligns = self.run.aligns.unwrap_or_default();
+
+        let children = std::mem::take(&mut self.run.layouts);
+        for (offset, child) in children {
+            let cross = if dirs.cross.is_positive() {
+                offset
+            } else {
+                self.run.size.cross - offset - child.size.get(dirs.cross.axis())
+            };
+
+            let pos = Gen::new(Length::ZERO, cross).switch(dirs).to_point();
+            layout.push_layout(pos, child);
+        }
+
+        self.stack.push_box(layout, aligns);
+        self.stack.push_spacing(self.ctx.line_spacing);
+        self.run = LineRun::new();
+    }
+
+    fn finish_line_if_not_empty(&mut self) {
+        if !self.line_is_empty() {
+            self.finish_line()
+        }
+    }
+}
+
+/// A sequence of boxes with the same alignment. A real line can consist of
+/// multiple runs with different alignments.
+struct LineRun {
+    /// The so-far accumulated items of the run.
+    layouts: Vec<(Length, BoxLayout)>,
+    /// The summed width and maximal height of the run.
+    size: Gen<Length>,
+    /// The alignment of all layouts in the line.
+    ///
+    /// When a new run is created the alignment is yet to be determined and
+    /// `None` as such. Once a layout is added, its alignment decides the
+    /// alignment for the whole run.
+    aligns: Option<Gen<Align>>,
+    /// The amount of cross-space left by another run on the same line or `None`
+    /// if this is the only run so far.
+    usable: Option<Length>,
+}
+
+impl LineRun {
+    fn new() -> Self {
+        Self {
+            layouts: vec![],
+            size: Gen::ZERO,
+            aligns: None,
+            usable: None,
+        }
+    }
+}
+
+/// Performs the stack layouting.
+pub(super) struct StackLayouter {
+    /// The context used for stack layouting.
+    pub ctx: StackContext,
+    /// The finished layouts.
+    pub layouts: Vec<BoxLayout>,
+    /// The in-progress space.
+    pub space: Space,
+}
+
+/// The context for stack layouting.
+#[derive(Debug, Clone)]
+pub(super) struct StackContext {
+    /// The layouting directions.
+    pub dirs: Gen<Dir>,
+    /// The spaces to layout into.
+    pub spaces: Vec<LayoutSpace>,
+    /// Whether to spill over into copies of the last space or finish layouting
+    /// when the last space is used up.
+    pub repeat: bool,
+    /// Whether to expand the size of the resulting layout to the full size of
+    /// this space or to shrink it to fit the content.
+    pub expand: Spec<bool>,
+}
+
+impl StackLayouter {
+    /// Create a new stack layouter.
+    pub fn new(ctx: StackContext) -> Self {
+        let space = ctx.spaces[0];
+        Self {
+            ctx,
+            layouts: vec![],
+            space: Space::new(0, true, space.size),
+        }
+    }
+
+    /// Add a layout to the stack.
+    pub fn push_box(&mut self, layout: BoxLayout, aligns: Gen<Align>) {
+        // If the alignment cannot be fitted in this space, finish it.
+        //
+        // TODO: Issue warning for non-fitting alignment in non-repeating
+        //       context.
+        if aligns.main < self.space.allowed_align && self.ctx.repeat {
+            self.finish_space(true);
+        }
+
+        // TODO: Issue warning about overflow if there is overflow in a
+        //       non-repeating context.
+        if !self.space.usable.fits(layout.size) && self.ctx.repeat {
+            self.skip_to_fitting_space(layout.size);
+        }
+
+        // Change the usable space and size of the space.
+        self.update_metrics(layout.size.switch(self.ctx.dirs));
+
+        // Add the box to the vector and remember that spacings are allowed
+        // again.
+        self.space.layouts.push((layout, aligns));
+        self.space.allowed_align = aligns.main;
+    }
+
+    /// Add spacing to the stack.
+    pub fn push_spacing(&mut self, mut spacing: Length) {
+        // Reduce the spacing such that it definitely fits.
+        let axis = self.ctx.dirs.main.axis();
+        spacing = spacing.min(self.space.usable.get(axis));
+
+        let size = Gen::new(spacing, Length::ZERO);
+        self.update_metrics(size);
+        self.space.layouts.push((
+            BoxLayout::new(size.switch(self.ctx.dirs).to_size()),
+            Gen::default(),
+        ));
+    }
+
+    fn update_metrics(&mut self, added: Gen<Length>) {
+        let mut used = self.space.used.switch(self.ctx.dirs);
+        used.cross = used.cross.max(added.cross);
+        used.main += added.main;
+        self.space.used = used.switch(self.ctx.dirs).to_size();
+        *self.space.usable.get_mut(self.ctx.dirs.main.axis()) -= added.main;
+    }
+
+    /// Move to the first space that can fit the given size or do nothing
+    /// if no space is capable of that.
+    pub fn skip_to_fitting_space(&mut self, size: Size) {
+        let start = self.next_space();
+        for (index, space) in self.ctx.spaces[start ..].iter().enumerate() {
+            if space.size.fits(size) {
+                self.finish_space(true);
+                self.start_space(start + index, true);
+                break;
+            }
+        }
+    }
+
+    /// The remaining inner spaces. If something is laid out into these spaces,
+    /// it will fit into this stack.
+    pub fn remaining(&self) -> Vec<LayoutSpace> {
+        let mut spaces = vec![LayoutSpace {
+            base: self.space.size,
+            size: self.space.usable,
+        }];
+
+        spaces.extend(&self.ctx.spaces[self.next_space() ..]);
+        spaces
+    }
+
+    /// The remaining usable size.
+    pub fn usable(&self) -> Size {
+        self.space.usable
+    }
+
+    /// Whether the current layout space is empty.
+    pub fn space_is_empty(&self) -> bool {
+        self.space.used == Size::ZERO && self.space.layouts.is_empty()
+    }
+
+    /// Finish everything up and return the final collection of boxes.
+    pub fn finish(mut self) -> Vec<BoxLayout> {
+        if self.space.hard || !self.space_is_empty() {
+            self.finish_space(false);
+        }
+        self.layouts
+    }
+
+    /// Finish active current space and start a new one.
+    pub fn finish_space(&mut self, hard: bool) {
+        let dirs = self.ctx.dirs;
+        let main = dirs.main.axis();
+
+        let space = self.ctx.spaces[self.space.index];
+        let layout_size = {
+            let mut used_size = self.space.used;
+            if self.ctx.expand.horizontal {
+                used_size.width = space.size.width;
+            }
+            if self.ctx.expand.vertical {
+                used_size.height = space.size.height;
+            }
+            used_size
+        };
+
+        let mut sum = Length::ZERO;
+        let mut sums = Vec::with_capacity(self.space.layouts.len() + 1);
+
+        for (boxed, _) in &self.space.layouts {
+            sums.push(sum);
+            sum += boxed.size.get(main);
+        }
+
+        sums.push(sum);
+
+        let mut layout = BoxLayout::new(layout_size);
+        let used = layout_size.switch(dirs);
+
+        let children = std::mem::take(&mut self.space.layouts);
+        for (i, (boxed, aligns)) in children.into_iter().enumerate() {
+            let size = boxed.size.switch(dirs);
+
+            let before = sums[i];
+            let after = sum - sums[i + 1];
+            let main_len = used.main - size.main;
+            let main_range = if dirs.main.is_positive() {
+                before .. main_len - after
+            } else {
+                main_len - before .. after
+            };
+
+            let cross_len = used.cross - size.cross;
+            let cross_range = if dirs.cross.is_positive() {
+                Length::ZERO .. cross_len
+            } else {
+                cross_len .. Length::ZERO
+            };
+
+            let main = aligns.main.apply(main_range);
+            let cross = aligns.cross.apply(cross_range);
+            let pos = Gen::new(main, cross).switch(dirs).to_point();
+
+            layout.push_layout(pos, boxed);
+        }
+
+        self.layouts.push(layout);
+
+        // ------------------------------------------------------------------ //
+        // Step 5: Start the next space.
+
+        self.start_space(self.next_space(), hard)
+    }
+
+    fn start_space(&mut self, index: usize, hard: bool) {
+        let space = self.ctx.spaces[index];
+        self.space = Space::new(index, hard, space.size);
+    }
+
+    fn next_space(&self) -> usize {
+        (self.space.index + 1).min(self.ctx.spaces.len() - 1)
+    }
+}
+
+/// A layout space composed of subspaces which can have different directions and
+/// alignments.
+#[derive(Debug)]
+pub(super) struct Space {
+    /// The index of this space in `ctx.spaces`.
+    index: usize,
+    /// Whether to include a layout for this space even if it would be empty.
+    hard: bool,
+    /// The so-far accumulated layouts.
+    layouts: Vec<(BoxLayout, Gen<Align>)>,
+    /// The full size of this space.
+    size: Size,
+    /// The used size of this space.
+    used: Size,
+    /// The remaining space.
+    usable: Size,
+    /// Which alignments for new boxes are still allowed.
+    pub(super) allowed_align: Align,
+}
+
+impl Space {
+    fn new(index: usize, hard: bool, size: Size) -> Self {
+        Self {
+            index,
+            hard,
+            layouts: vec![],
+            size,
+            used: Size::ZERO,
+            usable: size,
+            allowed_align: Align::Start,
+        }
+    }
+}