Generalize tree layouter 🌲

10 files changed, 153 insertions, 156 deletions

diff --git a/src/export/pdf.rs b/src/export/pdf.rs
index bb688118..76fc59b8 100644
--- a/src/export/pdf.rs
+++ b/src/export/pdf.rs
@@ -249,8 +249,8 @@ impl<'d, W: Write> ExportProcess<'d, W> {
                 },
 
                 LayoutAction::SetFont(id, size) => {
-                    active_font = (self.font_remap[id], *size);
-                    text.tf(active_font.0 as u32 + 1, *size);
+                    active_font = (self.font_remap[id], size.to_pt());
+                    text.tf(active_font.0 as u32 + 1, size.to_pt());
                 }
 
                 LayoutAction::WriteText(string) => {
diff --git a/src/func/mod.rs b/src/func/mod.rs
index bd61204e..fa6407d8 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, LayoutContext, MultiLayout};
-    pub use crate::layout::{Flow, Alignment, LayoutError, LayoutResult};
+    pub use crate::layout::{layout_tree, Layout, MultiLayout, LayoutContext, LayoutSpace};
+    pub use crate::layout::{LayoutAxes, AlignedAxis, Axis, 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};
     pub use crate::size::{Size, Size2D, SizeBox};
@@ -88,13 +89,16 @@ where T: Debug + PartialEq + 'static
 #[derive(Debug)]
 pub enum Command<'a> {
     LayoutTree(&'a SyntaxTree),
+
     Add(Layout),
-    AddMany(MultiLayout),
-    AddFlex(Layout),
-    SetAlignment(Alignment),
-    SetStyle(TextStyle),
-    FinishLayout,
+    AddMultiple(MultiLayout),
+
     FinishFlexRun,
+    FinishFlexLayout,
+    FinishLayout,
+
+    SetStyle(TextStyle),
+    SetAxes(LayoutAxes),
 }
 
 /// A sequence of commands requested for execution by a function.
diff --git a/src/layout/actions.rs b/src/layout/actions.rs
index 707d6113..ed3bc182 100644
--- a/src/layout/actions.rs
+++ b/src/layout/actions.rs
@@ -4,7 +4,7 @@ use std::fmt::{self, Display, Formatter};
 use std::io::{self, Write};
 
 use super::Layout;
-use crate::size::Size2D;
+use crate::size::{Size, Size2D};
 use LayoutAction::*;
 
 /// A layouting action.
@@ -13,7 +13,7 @@ pub enum LayoutAction {
     /// Move to an absolute position.
     MoveAbsolute(Size2D),
     /// Set the font by index and font size.
-    SetFont(usize, f32),
+    SetFont(usize, Size),
     /// Write text starting at the current position.
     WriteText(String),
     /// Visualize a box for debugging purposes.
@@ -26,7 +26,7 @@ impl LayoutAction {
     pub fn serialize<W: Write>(&self, f: &mut W) -> io::Result<()> {
         match self {
             MoveAbsolute(s) => write!(f, "m {:.4} {:.4}", s.x.to_pt(), s.y.to_pt()),
-            SetFont(i, s) => write!(f, "f {} {}", i, s),
+            SetFont(i, s) => write!(f, "f {} {}", i, s.to_pt()),
             WriteText(s) => write!(f, "w {}", s),
             DebugBox(p, s) => write!(
                 f,
@@ -69,9 +69,9 @@ debug_display!(LayoutAction);
 pub struct LayoutActionList {
     pub origin: Size2D,
     actions: Vec<LayoutAction>,
-    active_font: (usize, f32),
+    active_font: (usize, Size),
     next_pos: Option<Size2D>,
-    next_font: Option<(usize, f32)>,
+    next_font: Option<(usize, Size)>,
 }
 
 impl LayoutActionList {
@@ -80,7 +80,7 @@ impl LayoutActionList {
         LayoutActionList {
             actions: vec![],
             origin: Size2D::zero(),
-            active_font: (std::usize::MAX, 0.0),
+            active_font: (std::usize::MAX, Size::zero()),
             next_pos: None,
             next_font: None,
         }
diff --git a/src/layout/flex.rs b/src/layout/flex.rs
index a364b608..c136ad0d 100644
--- a/src/layout/flex.rs
+++ b/src/layout/flex.rs
@@ -75,16 +75,18 @@ impl FlexLayouter {
         }
     }
 
-    /// This layouter's context.
-    pub fn ctx(&self) -> FlexContext {
-        self.ctx
-    }
-
     /// Add a sublayout.
     pub fn add(&mut self, layout: Layout) {
         self.units.push(FlexUnit::Boxed(layout));
     }
 
+    /// Add multiple sublayouts from a multi-layout.
+    pub fn add_multiple(&mut self, layouts: MultiLayout) {
+        for layout in layouts {
+            self.add(layout);
+        }
+    }
+
     /// Add a space box which can be replaced by a run break.
     pub fn add_space(&mut self, space: Size) {
         self.units.push(FlexUnit::Space(space));
@@ -181,6 +183,11 @@ impl FlexLayouter {
         Ok(())
     }
 
+    /// This layouter's context.
+    pub fn ctx(&self) -> FlexContext {
+        self.ctx
+    }
+
     /// Whether this layouter contains any items.
     pub fn is_empty(&self) -> bool {
         self.units.is_empty()
diff --git a/src/layout/mod.rs b/src/layout/mod.rs
index f0160f31..2bafd792 100644
--- a/src/layout/mod.rs
+++ b/src/layout/mod.rs
@@ -192,7 +192,7 @@ impl LayoutSpace {
 }
 
 /// The axes along which the content is laid out.
-#[derive(Debug, Copy, Clone)]
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub struct LayoutAxes {
     pub primary: AlignedAxis,
     pub secondary: AlignedAxis,
diff --git a/src/layout/stacked.rs b/src/layout/stacked.rs
index 419ec6b7..cc6caa5e 100644
--- a/src/layout/stacked.rs
+++ b/src/layout/stacked.rs
@@ -1,3 +1,4 @@
+use smallvec::smallvec;
 use super::*;
 
 /// Layouts boxes stack-like.
@@ -66,7 +67,7 @@ impl StackLayouter {
     }
 
     /// Add multiple sublayouts from a multi-layout.
-    pub fn add_many(&mut self, layouts: MultiLayout) -> LayoutResult<()> {
+    pub fn add_multiple(&mut self, layouts: MultiLayout) -> LayoutResult<()> {
         for layout in layouts {
             self.add(layout)?;
         }
@@ -135,7 +136,7 @@ impl StackLayouter {
     /// finishing this stack. Otherwise, the new layout only appears if new
     /// content is added to it.
     fn start_new_space(&mut self, include_empty: bool) {
-        self.active_space = (self.active_space + 1).min(self.ctx.spaces.len() - 1);
+        self.active_space = self.next_space();
         self.usable = self.ctx.spaces[self.active_space].usable().generalized(self.ctx.axes);
         self.dimensions = start_dimensions(self.usable, self.ctx.axes);
         self.include_empty = include_empty;
@@ -151,10 +152,20 @@ impl StackLayouter {
         self.usable
     }
 
-    /// The (specialized) remaining area for new layouts in the current space.
-    pub fn remaining(&self) -> Size2D {
-        Size2D::new(self.usable.x, self.usable.y - self.dimensions.y)
-            .specialized(self.ctx.axes)
+    /// The remaining spaces for new layouts in the current space.
+    pub fn remaining(&self, shrink_to_fit: bool) -> LayoutSpaces {
+        let mut spaces = smallvec![LayoutSpace {
+            dimensions: Size2D::new(self.usable.x, self.usable.y - self.dimensions.y)
+                .specialized(self.ctx.axes),
+            padding: SizeBox::zero(),
+            shrink_to_fit,
+        }];
+
+        for space in &self.ctx.spaces[self.next_space()..] {
+            spaces.push(space.usable_space(shrink_to_fit));
+        }
+
+        spaces
     }
 
     /// Whether this layouter is in its last space.
@@ -162,6 +173,10 @@ impl StackLayouter {
         self.active_space == self.ctx.spaces.len() - 1
     }
 
+    fn next_space(&self) -> usize {
+        (self.active_space + 1).min(self.ctx.spaces.len() - 1)
+    }
+
     /// The combined size of the so-far included boxes with the other size.
     fn size_with(&self, other: Size2D) -> Size2D {
         Size2D {
diff --git a/src/layout/text.rs b/src/layout/text.rs
index 79ace040..88d83ab7 100644
--- a/src/layout/text.rs
+++ b/src/layout/text.rs
@@ -13,16 +13,6 @@ pub struct TextContext<'a, 'p> {
     pub style: &'a TextStyle,
 }
 
-impl<'a, 'p> TextContext<'a, 'p> {
-    /// Create a text context from a generic layout context.
-    pub fn from_layout_ctx(ctx: LayoutContext<'a, 'p>) -> TextContext<'a, 'p> {
-        TextContext {
-            loader: ctx.loader,
-            style: ctx.style,
-        }
-    }
-}
-
 /// Layouts text into a box.
 ///
 /// There is no complex layout involved. The text is simply laid out left-
@@ -81,7 +71,7 @@ impl<'a, 'p> TextLayouter<'a, 'p> {
         }
 
         Ok(Layout {
-            dimensions: Size2D::new(self.width, Size::pt(self.ctx.style.font_size)),
+            dimensions: Size2D::new(self.width, self.ctx.style.font_size),
             actions: self.actions.into_vec(),
             debug_render: false,
         })
@@ -107,15 +97,16 @@ impl<'a, 'p> TextLayouter<'a, 'p> {
                 let glyph = font
                     .read_table::<CharMap>()?
                     .get(c)
-                    .expect("layout text: font should have char");
+                    .expect("select_font: font should have char");
 
                 let glyph_width = font
                     .read_table::<HorizontalMetrics>()?
                     .get(glyph)
-                    .expect("layout text: font should have glyph")
+                    .expect("select_font: font should have glyph")
                     .advance_width as f32;
 
-                let char_width = font_unit_to_size(glyph_width) * self.ctx.style.font_size;
+                let char_width = font_unit_to_size(glyph_width)
+                    * self.ctx.style.font_size.to_pt();
 
                 return Ok((index, char_width));
             }
diff --git a/src/layout/tree.rs b/src/layout/tree.rs
index b64dd6eb..ca2051f4 100644
--- a/src/layout/tree.rs
+++ b/src/layout/tree.rs
@@ -13,8 +13,6 @@ struct TreeLayouter<'a, 'p> {
     stack: StackLayouter,
     flex: FlexLayouter,
     style: Cow<'a, TextStyle>,
-    alignment: Alignment,
-    set_newline: bool,
 }
 
 impl<'a, 'p> TreeLayouter<'a, 'p> {
@@ -22,51 +20,41 @@ impl<'a, 'p> TreeLayouter<'a, 'p> {
     fn new(ctx: LayoutContext<'a, 'p>) -> TreeLayouter<'a, 'p> {
         TreeLayouter {
             ctx,
-            stack: StackLayouter::new(StackContext::from_layout_ctx(ctx)),
+            stack: StackLayouter::new(StackContext {
+                spaces: ctx.spaces,
+                axes: ctx.axes,
+            }),
             flex: FlexLayouter::new(FlexContext {
-                space: ctx.space.usable_space(),
-                followup_spaces: ctx.followup_spaces.map(|s| s.usable_space()),
-                shrink_to_fit: true,
-                .. FlexContext::from_layout_ctx(ctx, flex_spacing(&ctx.style))
+                flex_spacing: flex_spacing(&ctx.style),
+                spaces: ctx.spaces.iter().map(|space| space.usable_space(true)).collect(),
+                axes: ctx.axes,
             }),
             style: Cow::Borrowed(ctx.style),
-            alignment: ctx.alignment,
-            set_newline: false,
         }
     }
 
-    /// Layout the tree into a box.
+    /// Layout a syntax tree.
     fn layout(&mut self, tree: &SyntaxTree) -> LayoutResult<()> {
         for node in &tree.nodes {
             match &node.val {
                 Node::Text(text) => {
-                    let layout = self.layout_text(text)?;
-                    self.flex.add(layout);
-                    self.set_newline = true;
+                    self.flex.add(layout_text(text, TextContext {
+                        loader: &self.ctx.loader,
+                        style: &self.style,
+                    })?);
                 }
 
                 Node::Space => {
-                    // Only add a space if there was any content before.
                     if !self.flex.is_empty() {
-                        let layout = self.layout_text(" ")?;
-                        self.flex.add_glue(layout.dimensions);
+                        self.flex.add_space(self.style.word_spacing * self.style.font_size);
                     }
                 }
-
-                // Finish the current flex layouting process.
                 Node::Newline => {
-                    self.finish_flex()?;
-
-                    if self.set_newline {
-                        let space = paragraph_spacing(&self.style);
-                        self.stack.add_space(space);
-                        self.set_newline = false;
+                    if !self.flex.is_empty() {
+                        self.finish_paragraph()?;
                     }
-
-                    self.start_new_flex();
                 }
 
-                // Toggle the text styles.
                 Node::ToggleItalics => self.style.to_mut().toggle_class(FontClass::Italic),
                 Node::ToggleBold => self.style.to_mut().toggle_class(FontClass::Bold),
                 Node::ToggleMonospace => self.style.to_mut().toggle_class(FontClass::Monospace),
@@ -78,115 +66,98 @@ impl<'a, 'p> TreeLayouter<'a, 'p> {
         Ok(())
     }
 
-    /// Finish the layout.
-    fn finish(mut self) -> LayoutResult<MultiLayout> {
-        self.finish_flex()?;
-        Ok(self.stack.finish())
-    }
-
     /// Layout a function.
     fn layout_func(&mut self, func: &FuncCall) -> LayoutResult<()> {
         // Finish the current flex layout on a copy to find out how
         // much space would be remaining if we finished.
+        let mut lookahead = self.stack.clone();
+        lookahead.add_multiple(self.flex.clone().finish()?)?;
+        let spaces = lookahead.remaining(true);
 
-        let mut lookahead_stack = self.stack.clone();
-        let layouts = self.flex.clone().finish()?;
-        lookahead_stack.add_many(layouts)?;
-        let remaining = lookahead_stack.remaining();
-
-        let mut ctx = self.ctx;
-        ctx.style = &self.style;
-        ctx.flow = Flow::Vertical;
-        ctx.shrink_to_fit = true;
-        ctx.space.dimensions = remaining;
-        ctx.space.padding = SizeBox::zero();
-        if let Some(space) = ctx.followup_spaces.as_mut() {
-            *space = space.usable_space();
-        }
-
-        let commands = func.body.val.layout(ctx)?;
+        let commands = func.body.val.layout(LayoutContext {
+            style: &self.style,
+            spaces,
+            .. self.ctx
+        })?;
 
         for command in commands {
-            match command {
-                Command::LayoutTree(tree) => self.layout(tree)?,
-
-                Command::Add(layout) => {
-                    self.finish_flex()?;
-                    self.stack.add(layout)?;
-                    self.set_newline = true;
-                    self.start_new_flex();
-                }
+            self.execute(command)?;
+        }
 
-                Command::AddMany(layouts) => {
-                    self.finish_flex()?;
-                    self.stack.add_many(layouts)?;
-                    self.set_newline = true;
-                    self.start_new_flex();
-                }
+        Ok(())
+    }
 
-                Command::AddFlex(layout) => self.flex.add(layout),
+    fn execute(&mut self, command: Command) -> LayoutResult<()> {
+        match command {
+            Command::LayoutTree(tree) => self.layout(tree)?,
 
-                Command::SetAlignment(alignment) => {
-                    self.finish_flex()?;
-                    self.alignment = alignment;
-                    self.start_new_flex();
-                }
+            Command::Add(layout) => self.flex.add(layout),
+            Command::AddMultiple(layouts) => self.flex.add_multiple(layouts),
 
-                Command::SetStyle(style) => *self.style.to_mut() = style,
+            Command::FinishFlexRun => self.flex.add_break(),
+            Command::FinishFlexLayout => self.finish_paragraph()?,
+            Command::FinishLayout => self.finish_layout(true)?,
 
-                Command::FinishLayout => {
-                    self.finish_flex()?;
-                    self.stack.finish_layout(true);
-                    self.start_new_flex();
+            Command::SetStyle(style) => *self.style.to_mut() = style,
+            Command::SetAxes(axes) => {
+                if axes.secondary != self.ctx.axes.secondary {
+                    self.stack.set_axis(axes.secondary);
+                } else if axes.primary != self.ctx.axes.primary {
+                    self.flex.set_axis(axes.primary);
                 }
 
-                Command::FinishFlexRun => self.flex.add_break(),
+                self.ctx.axes = axes;
             }
         }
 
         Ok(())
     }
 
-    /// Add text to the flex layout. If `glue` is true, the text will be a glue
-    /// part in the flex layouter. For details, see [`FlexLayouter`].
-    fn layout_text(&mut self, text: &str) -> LayoutResult<Layout> {
-        let ctx = TextContext {
-            loader: &self.ctx.loader,
-            style: &self.style,
-        };
+    /// Finish the layout.
+    fn finish(mut self) -> LayoutResult<MultiLayout> {
+        self.finish_flex()?;
+        Ok(self.stack.finish())
+    }
 
-        layout_text(text, ctx)
+    /// Finish the current stack layout.
+    fn finish_layout(&mut self, include_empty: bool) -> LayoutResult<()> {
+        self.finish_flex()?;
+        self.stack.finish_layout(include_empty);
+        self.start_new_flex();
+        Ok(())
+    }
+
+    /// Finish the current flex layout and add space after it.
+    fn finish_paragraph(&mut self) -> LayoutResult<()> {
+        self.finish_flex()?;
+        self.stack.add_space(paragraph_spacing(&self.style));
+        self.start_new_flex();
+        Ok(())
     }
 
     /// Finish the current flex layout and add it the stack.
     fn finish_flex(&mut self) -> LayoutResult<()> {
-        if self.flex.is_empty() {
-            return Ok(());
+        if !self.flex.is_empty() {
+            let layouts = self.flex.finish()?;
+            self.stack.add_multiple(layouts)?;
         }
-
-        let layouts = self.flex.finish()?;
-        self.stack.add_many(layouts)?;
-
         Ok(())
     }
 
     /// Start a new flex layout.
     fn start_new_flex(&mut self) {
-        let mut ctx = self.flex.ctx();
-        ctx.space.dimensions = self.stack.remaining();
-        ctx.alignment = self.alignment;
-        ctx.flex_spacing = flex_spacing(&self.style);
-
-        self.flex = FlexLayouter::new(ctx);
+        self.flex = FlexLayouter::new(FlexContext {
+            flex_spacing: flex_spacing(&self.style),
+            spaces: self.stack.remaining(true),
+            axes: self.ctx.axes,
+        });
     }
 }
 
 fn flex_spacing(style: &TextStyle) -> Size {
-    (style.line_spacing - 1.0) * Size::pt(style.font_size)
+    (style.line_spacing - 1.0) * style.font_size
 }
 
 fn paragraph_spacing(style: &TextStyle) -> Size {
-    let line_height = Size::pt(style.font_size);
-    let space_factor = style.line_spacing * style.paragraph_spacing - 1.0;
-    line_height * space_factor
+    (style.paragraph_spacing - 1.0) * style.font_size
 }
diff --git a/src/library/structure.rs b/src/library/structure.rs
index e6d242a0..2bcd2744 100644
--- a/src/library/structure.rs
+++ b/src/library/structure.rs
@@ -1,30 +1,36 @@
 use crate::func::prelude::*;
 use Command::*;
 
-/// 📜 `page.break`: Ends the current page.
+/// ↩ `line.break`, `n`: Ends the current line.
 #[derive(Debug, PartialEq)]
-pub struct Pagebreak;
+pub struct Linebreak;
 
 function! {
-    data: Pagebreak,
+    data: Linebreak,
     parse: plain,
-
-    layout(_, _) {
-        Ok(commands![FinishLayout])
-    }
+    layout(_, _) { Ok(commands![FinishFlexRun]) }
 }
 
-/// 🔙 `line.break`, `n`: Ends the current line.
+/// ↕ `paragraph.break`: Ends the current paragraph.
+///
+/// This has the same effect as two subsequent newlines.
 #[derive(Debug, PartialEq)]
-pub struct Linebreak;
+pub struct Parbreak;
 
 function! {
-    data: Linebreak,
+    data: Parbreak,
     parse: plain,
+    layout(_, _) { Ok(commands![FinishFlexLayout]) }
+}
 
-    layout(_, _) {
-        Ok(commands![FinishFlexRun])
-    }
+/// 📜 `page.break`: Ends the current page.
+#[derive(Debug, PartialEq)]
+pub struct Pagebreak;
+
+function! {
+    data: Pagebreak,
+    parse: plain,
+    layout(_, _) { Ok(commands![FinishLayout]) }
 }
 
 /// 📐 `align`: Aligns content in different ways.
diff --git a/src/style.rs b/src/style.rs
index 68bd9a27..e2ab0937 100644
--- a/src/style.rs
+++ b/src/style.rs
@@ -13,7 +13,9 @@ pub struct TextStyle {
     /// leftmost possible one.
     pub fallback: Vec<FontClass>,
     /// The font size.
-    pub font_size: f32,
+    pub font_size: Size,
+    /// The word spacing (as a multiple of the font size).
+    pub word_spacing: f32,
     /// The line spacing (as a multiple of the font size).
     pub line_spacing: f32,
     /// The paragraphs spacing (as a multiple of the font size).
@@ -63,7 +65,8 @@ impl Default for TextStyle {
         TextStyle {
             classes: vec![Regular],
             fallback: vec![Serif],
-            font_size: 11.0,
+            font_size: Size::pt(11.0),
+            word_spacing: 0.25,
             line_spacing: 1.2,
             paragraph_spacing: 1.5,
         }