First half of stack update 🌓

7 files changed, 202 insertions, 121 deletions

diff --git a/src/func/mod.rs b/src/func/mod.rs
index 126fd824..33a6c756 100644
--- a/src/func/mod.rs
+++ b/src/func/mod.rs
@@ -12,8 +12,9 @@ pub mod helpers;
 /// Useful imports for creating your own functions.
 pub mod prelude {
     pub use crate::func::{Command, CommandList, Function};
-    pub use crate::layout::{layout_tree, Layout, MultiLayout, LayoutContext, LayoutSpace};
-    pub use crate::layout::{LayoutAxes, Axis, Alignment};
+    pub use crate::layout::{layout_tree, Layout, MultiLayout, LayoutContext};
+    pub use crate::layout::{LayoutSpace, LayoutSpaces, SpacingKind};
+    pub use crate::layout::{LayoutAxes, Axis, AxisKind, LayoutAlignment, Alignment};
     pub use crate::layout::{LayoutError, LayoutResult};
     pub use crate::syntax::{SyntaxTree, FuncHeader, FuncArgs, Expression, Spanned, Span};
     pub use crate::syntax::{parse, ParseContext, ParseError, ParseResult};
@@ -96,19 +97,16 @@ pub enum Command<'a> {
 
     Add(Layout),
     AddMultiple(MultiLayout),
-
-    AddPrimarySpace(Size),
-    AddSecondarySpace(Size),
+    AddSpacing(Size, SpacingKind, AxisKind),
 
     FinishLine,
     FinishRun,
     FinishSpace,
-
     BreakParagraph,
 
     SetTextStyle(TextStyle),
     SetPageStyle(PageStyle),
-
+    SetAlignment(LayoutAlignment),
     SetAxes(LayoutAxes),
 }
 
diff --git a/src/layout/flex.rs b/src/layout/flex.rs
index 96b2aa85..afca23ec 100644
--- a/src/layout/flex.rs
+++ b/src/layout/flex.rs
@@ -62,7 +62,7 @@ impl PartialLine {
 pub struct FlexContext {
     pub spaces: LayoutSpaces,
     pub axes: LayoutAxes,
-    pub expand: bool,
+    pub alignment: LayoutAlignment,
     pub flex_spacing: Size,
 }
 
@@ -110,7 +110,7 @@ impl FlexLayouter {
         if !self.run_is_empty() {
             self.finish_run()?;
         }
-        Ok(self.stack.add_space(space, kind))
+        Ok(self.stack.add_spacing(space, kind))
     }
 
     pub fn set_axes(&mut self, axes: LayoutAxes) {
@@ -179,7 +179,7 @@ impl FlexLayouter {
             debug_render: false,
         })?;
 
-        self.stack.add_space(self.flex_spacing, SpaceKind::Independent);
+        self.stack.add_spacing(self.flex_spacing, SpaceKind::Independent);
 
         let remaining = self.axes.specialize(Size2D {
             x: self.part.usable
diff --git a/src/layout/mod.rs b/src/layout/mod.rs
index 31064d40..f45ed10a 100644
--- a/src/layout/mod.rs
+++ b/src/layout/mod.rs
@@ -59,7 +59,7 @@ pub struct LayoutContext<'a, 'p> {
     pub spaces: LayoutSpaces,
     /// The initial axes along which content is laid out.
     pub axes: LayoutAxes,
-    /// The alignment for the two axes.
+    /// The alignment of the finished layout.
     pub alignment: LayoutAlignment,
 }
 
@@ -71,12 +71,12 @@ pub type LayoutSpaces = SmallVec<[LayoutSpace; 2]>;
 pub struct LayoutSpace {
     /// The maximum size of the box to layout in.
     pub dimensions: Size2D,
+    /// Padding that should be respected on each side.
+    pub padding: SizeBox,
     /// Whether to expand the dimensions of the resulting layout to the full
     /// dimensions of this space or to shrink them to fit the content for the
     /// vertical and horizontal axis.
     pub expand: (bool, bool),
-    /// Padding that should be respected on each side.
-    pub padding: SizeBox,
 }
 
 impl LayoutSpace {
@@ -95,8 +95,8 @@ impl LayoutSpace {
     pub fn usable_space(&self) -> LayoutSpace {
         LayoutSpace {
             dimensions: self.usable(),
-            expand: (false, false),
             padding: SizeBox::zero(),
+            expand: (false, false),
         }
     }
 }
@@ -110,6 +110,10 @@ pub struct LayoutAxes {
 
 impl LayoutAxes {
     pub fn new(primary: Axis, secondary: Axis) -> LayoutAxes {
+        if primary.is_horizontal() == secondary.is_horizontal() {
+            panic!("LayoutAxes::new: invalid parallel axes {:?} and {:?}", primary, secondary);
+        }
+
         LayoutAxes { primary, secondary }
     }
 
@@ -134,6 +138,13 @@ impl LayoutAxes {
     }
 }
 
+/// The two kinds of axes.
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub enum AxisKind {
+    Primary,
+    Secondary,
+}
+
 /// Directions along which content is laid out.
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub enum Axis {
diff --git a/src/layout/stack.rs b/src/layout/stack.rs
index fd88ce98..793c2044 100644
--- a/src/layout/stack.rs
+++ b/src/layout/stack.rs
@@ -11,29 +11,42 @@ pub struct StackLayouter {
     ctx: StackContext,
     /// The output layouts.
     layouts: MultiLayout,
-    /// The full layout space.
+    /// The currently active layout space.
     space: Space,
-    /// The currently active subspace.
+    /// The remaining subspace of the active space. Whenever the layouting axes
+    /// change a new subspace is started.
     sub: Subspace,
 }
 
+/// The context for stack layouting.
+///
+/// See [`LayoutContext`] for details about the fields.
+#[derive(Debug, Clone)]
+pub struct StackContext {
+    pub spaces: LayoutSpaces,
+    pub axes: LayoutAxes,
+    pub alignment: LayoutAlignment,
+}
+
+/// A layout space composed of subspaces which can have different axes and
+/// alignments.
 #[derive(Debug, Clone)]
 struct Space {
     /// The index of this space in the list of spaces.
     index: usize,
     /// Whether to add the layout for this space even if it would be empty.
     hard: bool,
-    /// The layouting actions accumulated from the subspaces.
-    actions: LayoutActionList,
-    /// The used size of this space from the top-left corner to
-    /// the bottomright-most point of used space (specialized).
-    combined_dimensions: Size2D,
+    /// The so-far accumulated subspaces.
+    spaces: Vec<Subspace>,
 }
 
+/// A part of a space with fixed axes and secondary alignment.
 #[derive(Debug, Clone)]
 struct Subspace {
     /// The axes along which contents in this subspace are laid out.
     axes: LayoutAxes,
+    /// The secondary alignment of this subspace.
+    alignment: Alignment,
     /// The beginning of this subspace in the parent space (specialized).
     origin: Size2D,
     /// The total usable space of this subspace (generalized).
@@ -43,45 +56,19 @@ struct Subspace {
     /// - `y` being the total extent of all boxes and space in the secondary
     ///   direction.
     size: Size2D,
-    /// The so-far accumulated (offset, anchor, box) triples.
-    boxes: Vec<(Size, Size, Layout)>,
-    /// The last added spacing if the last was spacing.
+    /// The so-far accumulated layouts.
+    layouts: Vec<LayoutEntry>,
+    /// The last added spacing if the last added thing was spacing.
     last_spacing: LastSpacing,
 }
 
-impl Space {
-    fn new(index: usize, hard: bool) -> Space {
-        Space {
-            index,
-            hard,
-            actions: LayoutActionList::new(),
-            combined_dimensions: Size2D::zero(),
-        }
-    }
-}
-
-impl Subspace {
-    fn new(origin: Size2D, usable: Size2D, axes: LayoutAxes) -> Subspace {
-        Subspace {
-            origin,
-            anchor: axes.anchor(usable),
-            factor: axes.secondary.axis.factor(),
-            boxes: vec![],
-            usable: axes.generalize(usable),
-            dimensions: Size2D::zero(),
-            space: LastSpacing::Forbidden,
-        }
-    }
-}
-
-/// The context for stack layouting.
-///
-/// See [`LayoutContext`] for details about the fields.
+/// A single layout in a subspace.
 #[derive(Debug, Clone)]
-pub struct StackContext {
-    pub spaces: LayoutSpaces,
-    pub axes: LayoutAxes,
-    pub expand: bool,
+struct LayoutEntry {
+    /// The offset of this box on the secondary axis.
+    offset: Size,
+    /// The layout itself.
+    layout: Layout,
 }
 
 impl StackLayouter {
@@ -94,41 +81,61 @@ impl StackLayouter {
             ctx,
             layouts: MultiLayout::new(),
             space: Space::new(0, true),
-            sub: Subspace::new(space.start(), space.usable(), axes),
+            sub: Subspace::new(axes, Alignment::Origin, space.start(), space.usable()),
         }
     }
 
+    /// Add a layout to the stack.
     pub fn add(&mut self, layout: Layout) -> LayoutResult<()> {
-        if let LastSpacing::Soft(space) = self.sub.space {
-            self.add_space(space, SpaceKind::Hard);
+        if layout.alignment.secondary != self.sub.alignment {
+            // self.finish_subspace();
+            // finish sub and start new with layout's alignment
         }
 
-        let size = self.ctx.axes.generalize(layout.dimensions);
+        // Add a cached soft space if there is one.
+        if let LastSpacing::Soft(space, _) = self.sub.last_spacing {
+            self.add_spacing(space, SpacingKind::Hard);
+        }
 
-        let mut new_dimensions = Size2D {
-            x: crate::size::max(self.sub.dimensions.x, size.x),
-            y: self.sub.dimensions.y + size.y
+        // The new primary size is the maximum of the current one and the
+        // layout's one while the secondary size grows by the layout's size.
+        let size = self.ctx.axes.generalize(layout.dimensions);
+        let mut new_size = Size2D {
+            x: crate::size::max(self.sub.size.x, size.x),
+            y: self.sub.size.y + size.y
         };
 
-        while !self.sub.usable.fits(new_dimensions) {
+        // Find the first (sub-)space that fits the layout.
+        while !self.sub.usable.fits(new_size) {
             if self.space_is_last() && self.space_is_empty() {
                 lerr!("box does not fit into stack");
             }
 
             self.finish_space(true);
-            new_dimensions = size;
+            new_size = size;
         }
 
-        let offset = self.sub.dimensions.y;
-        let anchor = self.ctx.axes.primary.anchor(size.x);
+        // The secondary offset from the start of layouts is given by the
+        // current primary size of the subspace.
+        let offset = self.sub.size.y;
+        self.sub.layouts.push(LayoutEntry {
+            offset,
+            layout,
+        });
+
+        // The new size of the subspace is the previously calculated
+        // combination.
+        self.sub.size = new_size;
 
-        self.sub.boxes.push((offset, anchor, layout));
-        self.sub.dimensions = new_dimensions;
-        self.sub.space = LastSpacing::Allowed;
+        // Since the last item was a box, last spacing is reset to `None`.
+        self.sub.last_spacing = LastSpacing::None;
 
         Ok(())
     }
 
+    /// Add multiple layouts to the stack.
+    ///
+    /// This function simply calls `add` for each layout.
     pub fn add_multiple(&mut self, layouts: MultiLayout) -> LayoutResult<()> {
         for layout in layouts {
             self.add(layout)?;
@@ -136,33 +143,55 @@ impl StackLayouter {
         Ok(())
     }
 
-    pub fn add_space(&mut self, space: Size, kind: SpaceKind) {
-        if kind == SpaceKind::Soft {
-            if self.sub.space != LastSpacing::Forbidden {
-                self.sub.space = LastSpacing::Soft(space);
-            }
-        } else {
-            if self.sub.dimensions.y + space > self.sub.usable.y {
-                self.sub.dimensions.y = self.sub.usable.y;
-            } else {
-                self.sub.dimensions.y += space;
+    /// Add secondary spacing to the stack.
+    pub fn add_spacing(&mut self, space: Size, kind: SpacingKind) {
+        match kind {
+            // A hard space is directly added to the sub's size.
+            SpacingKind::Hard => {
+                if self.sub.size.y + space > self.sub.usable.y {
+                    self.sub.size.y = self.sub.usable.y;
+                } else {
+                    self.sub.size.y += space;
+                }
+
+                self.sub.last_spacing = LastSpacing::Hard;
             }
 
-            if kind == SpaceKind::Hard {
-                self.sub.space = LastSpacing::Forbidden;
+            // A hard space is cached if it is not consumed by a hard space or
+            // previous soft space with higher level.
+            SpacingKind::Soft(level) => {
+                let consumes = match self.sub.last_spacing {
+                    LastSpacing::None => true,
+                    LastSpacing::Soft(_, prev) if level < prev => true,
+                    _ => false,
+                };
+
+                if consumes {
+                    self.sub.last_spacing = LastSpacing::Soft(space, level);
+                }
             }
         }
     }
 
+    /// Change the layouting axis used by this layouter.
+    ///
+    /// This starts a new subspace (if the axes are actually different from the
+    /// current ones).
     pub fn set_axes(&mut self, axes: LayoutAxes) {
         if axes != self.ctx.axes {
             self.finish_subspace();
+
             let (origin, usable) = self.remaining_subspace();
+            self.sub = Subspace::new(axes, Alignment::Origin, origin, usable);
             self.ctx.axes = axes;
-            self.sub = Subspace::new(origin, usable, axes);
         }
     }
 
+    /// Change the layouting spaces to use.
+    ///
+    /// If `replace_empty` is true, the current space is replaced if there are
+    /// no boxes laid into it yet. Otherwise, only the followup spaces are
+    /// replaced.
     pub fn set_spaces(&mut self, spaces: LayoutSpaces, replace_empty: bool) {
         if replace_empty && self.space_is_empty() {
             self.ctx.spaces = spaces;
@@ -173,10 +202,13 @@ impl StackLayouter {
         }
     }
 
+    /// The remaining unpadded, unexpanding spaces. If a multi-layout is laid
+    /// out into these spaces, it will fit into this stack.
     pub fn remaining(&self) -> LayoutSpaces {
         let mut spaces = smallvec![LayoutSpace {
             dimensions: self.remaining_subspace().1,
             padding: SizeBox::zero(),
+            expand: (false, false),
         }];
 
         for space in &self.ctx.spaces[self.next_space()..] {
@@ -186,20 +218,24 @@ impl StackLayouter {
         spaces
     }
 
+    /// The usable size along the primary axis.
     pub fn primary_usable(&self) -> Size {
         self.sub.usable.x
     }
 
+    /// Whether the current layout space (not subspace) is empty.
     pub fn space_is_empty(&self) -> bool {
-        self.space.combined_dimensions == Size2D::zero()
-            && self.space.actions.is_empty()
-            && self.sub.dimensions == Size2D::zero()
+        self.sub.layouts.is_empty()
+            && self.sub.size == Size2D::zero()
+            && self.space.spaces.is_empty()
     }
 
+    /// Whether the current layout space is the last is the followup list.
     pub fn space_is_last(&self) -> bool {
         self.space.index == self.ctx.spaces.len() - 1
     }
 
+    /// Compute the finished multi-layout.
     pub fn finish(mut self) -> MultiLayout {
         if self.space.hard || !self.space_is_empty() {
             self.finish_space(false);
@@ -212,29 +248,19 @@ impl StackLayouter {
 
         let space = self.ctx.spaces[self.space.index];
 
-        self.layouts.add(Layout {
+        self.layouts.push(Layout {
             dimensions: match self.ctx.expand {
                 true => space.dimensions,
                 false => self.space.combined_dimensions.padded(space.padding),
             },
-            actions: self.space.actions.to_vec(),
-            debug_render: true,
+            baseline: None,
+            alignment: self.ctx.alignment,
+            actions: actions.to_vec(),
         });
 
         self.start_space(self.next_space(), hard);
     }
 
-    fn start_space(&mut self, space: usize, hard: bool) {
-        self.space = Space::new(space, hard);
-
-        let space = self.ctx.spaces[space];
-        self.sub = Subspace::new(space.start(), space.usable(), self.ctx.axes);
-    }
-
-    fn next_space(&self) -> usize {
-        (self.space.index + 1).min(self.ctx.spaces.len() - 1)
-    }
-
     fn finish_subspace(&mut self) {
         let factor = self.ctx.axes.secondary.axis.factor();
         let anchor =
@@ -264,6 +290,18 @@ impl StackLayouter {
         self.space.combined_dimensions.max_eq(origin - space.start() + dimensions);
     }
 
+    /// Start a new space with the given index.
+    fn start_space(&mut self, space: usize, hard: bool) {
+        // Start the space.
+        self.space = Space::new(space, hard);
+
+        // Start the subspace.
+        let space = self.ctx.spaces[space];
+        let axes = self.ctx.axes;
+        self.sub = Subspace::new(axes, Alignment::Origin, space.start(), space.usable());
+    }
+
+    /// The remaining sub
     fn remaining_subspace(&self) -> (Size2D, Size2D) {
         let new_origin = self.sub.origin + match self.ctx.axes.secondary.axis.is_positive() {
             true => self.ctx.axes.specialize(Size2D::with_y(self.sub.dimensions.y)),
@@ -277,4 +315,32 @@ impl StackLayouter {
 
         (new_origin, new_usable)
     }
+
+    fn next_space(&self) -> usize {
+        (self.space.index + 1).min(self.ctx.spaces.len() - 1)
+    }
+}
+
+impl Space {
+    fn new(index: usize, hard: bool) -> Space {
+        Space {
+            index,
+            hard,
+            spaces: vec![],
+        }
+    }
+}
+
+impl Subspace {
+    fn new(axes: LayoutAxes, alignment: Alignment, origin: Size2D, usable: Size2D) -> Subspace {
+        Subspace {
+            axes,
+            alignment,
+            origin,
+            usable: axes.generalize(usable),
+            size: Size2D::zero(),
+            layouts: vec![],
+            last_spacing: LastSpacing::Hard,
+        }
+    }
 }
diff --git a/src/layout/text.rs b/src/layout/text.rs
index 3ca826ca..343127e3 100644
--- a/src/layout/text.rs
+++ b/src/layout/text.rs
@@ -11,6 +11,7 @@ use crate::size::{Size, Size2D};
 pub struct TextContext<'a, 'p> {
     pub loader: &'a SharedFontLoader<'p>,
     pub style: &'a TextStyle,
+    pub alignment: LayoutAlignment,
 }
 
 /// Layouts text into a box.
@@ -72,6 +73,8 @@ impl<'a, 'p> TextLayouter<'a, 'p> {
 
         Ok(Layout {
             dimensions: Size2D::new(self.width, self.ctx.style.font_size),
+            baseline: None,
+            alignment: self.ctx.alignment,
             actions: self.actions.to_vec(),
         })
     }
diff --git a/src/layout/tree.rs b/src/layout/tree.rs
index 9a818963..efa0c7b7 100644
--- a/src/layout/tree.rs
+++ b/src/layout/tree.rs
@@ -19,10 +19,10 @@ impl<'a, 'p> TreeLayouter<'a, 'p> {
     fn new(ctx: LayoutContext<'a, 'p>) -> TreeLayouter<'a, 'p> {
         TreeLayouter {
             flex: FlexLayouter::new(FlexContext {
-                flex_spacing: flex_spacing(&ctx.style.text),
                 spaces: ctx.spaces.clone(),
                 axes: ctx.axes,
-                expand: ctx.expand,
+                alignment: ctx.alignment,
+                flex_spacing: flex_spacing(&ctx.style.text),
             }),
             style: ctx.style.clone(),
             ctx,
@@ -52,6 +52,7 @@ impl<'a, 'p> TreeLayouter<'a, 'p> {
         let layout = layout_text(text, TextContext {
             loader: &self.ctx.loader,
             style: &self.style.text,
+            alignment: self.ctx.alignment,
         })?;
 
         Ok(self.flex.add(layout))
@@ -90,23 +91,25 @@ impl<'a, 'p> TreeLayouter<'a, 'p> {
     }
 
     fn execute(&mut self, command: Command) -> LayoutResult<()> {
-        match command {
-            Command::LayoutTree(tree) => self.layout(tree)?,
+        use Command::*;
 
-            Command::Add(layout) => self.flex.add(layout),
-            Command::AddMultiple(layouts) => self.flex.add_multiple(layouts),
-
-            Command::AddPrimarySpace(space) => self.flex.add_primary_space(space, SpacingKind::Hard),
-            Command::AddSecondarySpace(space) => self.flex.add_secondary_space(space, SpacingKind::Hard)?,
+        match command {
+            LayoutTree(tree) => self.layout(tree)?,
 
-            Command::FinishLine => self.flex.add_break(),
-            Command::FinishRun => { self.flex.finish_run()?; },
-            Command::FinishSpace => self.flex.finish_space(true)?,
+            Add(layout) => self.flex.add(layout),
+            AddMultiple(layouts) => self.flex.add_multiple(layouts),
+            AddSpacing(space, kind, axis) => match axis {
+                AxisKind::Primary => self.flex.add_primary_space(space, kind),
+                AxisKind::Secondary => self.flex.add_secondary_space(space, kind)?,
+            }
 
-            Command::BreakParagraph => self.layout_paragraph()?,
+            FinishLine => self.flex.add_break(),
+            FinishRun => { self.flex.finish_run()?; },
+            FinishSpace => self.flex.finish_space(true)?,
+            BreakParagraph => self.layout_paragraph()?,
 
-            Command::SetTextStyle(style) => self.style.text = style,
-            Command::SetPageStyle(style) => {
+            SetTextStyle(style) => self.style.text = style,
+            SetPageStyle(style) => {
                 if !self.ctx.top_level {
                     lerr!("page style cannot only be altered in the top-level context");
                 }
@@ -115,13 +118,13 @@ impl<'a, 'p> TreeLayouter<'a, 'p> {
                 self.flex.set_spaces(smallvec![
                     LayoutSpace {
                         dimensions: style.dimensions,
-                        expand: (true, true),
                         padding: style.margins,
+                        expand: (true, true),
                     }
                 ], true);
-            },
-
-            Command::SetAxes(axes) => {
+            }
+            SetAlignment(alignment) => self.ctx.alignment = alignment,
+            SetAxes(axes) => {
                 self.flex.set_axes(axes);
                 self.ctx.axes = axes;
             }
diff --git a/src/library/spacing.rs b/src/library/spacing.rs
index 869a6227..47fe9fff 100644
--- a/src/library/spacing.rs
+++ b/src/library/spacing.rs
@@ -65,7 +65,7 @@ enum Spacing {
 
 // FIXME: h != primary and v != secondary.
 space_func!(HorizontalSpace, "📖 `h`: Adds horizontal whitespace.",
-    space => AddPrimarySpace(space));
+    space => AddSpacing(space, SpacingKind::Hard, AxisKind::Primary));
 
 space_func!(VerticalSpace, "📑 `v`: Adds vertical whitespace.",
-    space => AddSecondarySpace(space));
+    space => AddSpacing(space, SpacingKind::Hard, AxisKind::Secondary));