Page style modification functions 📜

- `page.size`
- `page.margins`

11 files changed, 178 insertions, 52 deletions

diff --git a/src/func/mod.rs b/src/func/mod.rs
index 27dceee3..360c19f8 100644
--- a/src/func/mod.rs
+++ b/src/func/mod.rs
@@ -103,7 +103,9 @@ pub enum Command<'a> {
 
     BreakParagraph,
 
-    SetStyle(TextStyle),
+    SetTextStyle(TextStyle),
+    SetPageStyle(PageStyle),
+
     SetAxes(LayoutAxes),
 }
 
diff --git a/src/layout/flex.rs b/src/layout/flex.rs
index 0ad31521..142530a6 100644
--- a/src/layout/flex.rs
+++ b/src/layout/flex.rs
@@ -19,7 +19,9 @@ use super::*;
 /// However, it can be any layout.
 #[derive(Debug, Clone)]
 pub struct FlexLayouter {
-    ctx: FlexContext,
+    axes: LayoutAxes,
+    flex_spacing: Size,
+
     stack: StackLayouter,
     units: Vec<FlexUnit>,
 
@@ -69,14 +71,16 @@ impl FlexLayouter {
     /// Create a new flex layouter.
     pub fn new(ctx: FlexContext) -> FlexLayouter {
         let stack = StackLayouter::new(StackContext {
-            spaces: ctx.spaces.clone(),
+            spaces: ctx.spaces,
             axes: ctx.axes,
             shrink_to_fit: ctx.shrink_to_fit,
         });
 
         let usable = stack.usable().x;
         FlexLayouter {
-            ctx,
+            axes: ctx.axes,
+            flex_spacing: ctx.flex_spacing,
+
             units: vec![],
             stack,
 
@@ -126,6 +130,18 @@ impl FlexLayouter {
         self.units.push(FlexUnit::SetAxes(axes));
     }
 
+    /// Update the followup space to be used by this flex layouter.
+    pub fn set_spaces(&mut self, spaces: LayoutSpaces, replace_empty: bool) {
+        if replace_empty && self.box_is_empty() && self.stack.space_is_empty() {
+            self.stack.set_spaces(spaces, true);
+            self.total_usable = self.stack.usable().x;
+            self.usable = self.total_usable;
+            self.space = None;
+        } else {
+            self.stack.set_spaces(spaces, false);
+        }
+    }
+
     /// Compute the justified layout.
     ///
     /// The layouter is not consumed by this to prevent ownership problems
@@ -176,7 +192,7 @@ impl FlexLayouter {
     /// Layout a content box into the current flex run or start a new run if
     /// it does not fit.
     fn layout_box(&mut self, boxed: Layout) -> LayoutResult<()> {
-        let size = self.ctx.axes.generalize(boxed.dimensions);
+        let size = self.axes.generalize(boxed.dimensions);
 
         if size.x > self.size_left() {
             self.space = None;
@@ -213,7 +229,7 @@ impl FlexLayouter {
     }
 
     fn layout_set_axes(&mut self, axes: LayoutAxes) {
-        if axes.primary != self.ctx.axes.primary {
+        if axes.primary != self.axes.primary {
             self.finish_aligned_run();
 
             self.usable = match axes.primary.alignment {
@@ -231,11 +247,11 @@ impl FlexLayouter {
             };
         }
 
-        if axes.secondary != self.ctx.axes.secondary {
+        if axes.secondary != self.axes.secondary {
             self.stack.set_axes(axes);
         }
 
-        self.ctx.axes = axes;
+        self.axes = axes;
     }
 
     /// Finish the current flex run.
@@ -248,7 +264,7 @@ impl FlexLayouter {
 
         let actions = std::mem::replace(&mut self.merged_actions, LayoutActionList::new());
         self.stack.add(Layout {
-            dimensions: self.ctx.axes.specialize(self.merged_dimensions),
+            dimensions: self.axes.specialize(self.merged_dimensions),
             actions: actions.into_vec(),
             debug_render: false,
         })?;
@@ -265,38 +281,33 @@ impl FlexLayouter {
             return;
         }
 
-        let factor = if self.ctx.axes.primary.axis.is_positive() { 1 } else { -1 };
-        let anchor = self.ctx.axes.primary.anchor(self.total_usable)
-                     - self.ctx.axes.primary.anchor(self.run.size.x);
+        let factor = if self.axes.primary.axis.is_positive() { 1 } else { -1 };
+        let anchor = self.axes.primary.anchor(self.total_usable)
+                     - self.axes.primary.anchor(self.run.size.x);
 
         self.max_extent = crate::size::max(self.max_extent, anchor + factor * self.run.size.x);
 
         for (offset, layout) in self.run.content.drain(..) {
             let general_position = Size2D::with_x(anchor + factor * offset);
-            let position = self.ctx.axes.specialize(general_position);
+            let position = self.axes.specialize(general_position);
 
             self.merged_actions.add_layout(position, layout);
         }
 
-        self.merged_dimensions.x = match self.ctx.axes.primary.alignment {
+        self.merged_dimensions.x = match self.axes.primary.alignment {
             Alignment::Origin => self.run.size.x,
             Alignment::Center | Alignment::End => self.total_usable,
         };
 
         self.merged_dimensions.y = crate::size::max(
             self.merged_dimensions.y,
-            self.run.size.y + self.ctx.flex_spacing,
+            self.run.size.y + self.flex_spacing,
         );
 
         self.last_run_remaining = Size2D::new(self.size_left(), self.merged_dimensions.y);
         self.run.size = Size2D::zero();
     }
 
-    /// This layouter's context.
-    pub fn ctx(&self) -> &FlexContext {
-        &self.ctx
-    }
-
     pub fn remaining(&self) -> LayoutResult<(LayoutSpaces, LayoutSpaces)> {
         let mut future = self.clone();
         future.finish_box()?;
@@ -310,7 +321,6 @@ impl FlexLayouter {
         Ok((flex_spaces, stack_spaces))
     }
 
-    /// Whether this layouter contains any items.
     pub fn box_is_empty(&self) -> bool {
         !self.units.iter().any(|unit| matches!(unit, FlexUnit::Boxed(_)))
     }
diff --git a/src/layout/mod.rs b/src/layout/mod.rs
index a4514704..426a51ec 100644
--- a/src/layout/mod.rs
+++ b/src/layout/mod.rs
@@ -9,7 +9,7 @@ use toddle::Error as FontError;
 
 use crate::func::Command;
 use crate::size::{Size, Size2D, SizeBox};
-use crate::style::TextStyle;
+use crate::style::{PageStyle, TextStyle};
 use crate::syntax::{FuncCall, Node, SyntaxTree};
 
 mod actions;
@@ -131,9 +131,15 @@ pub struct LayoutContext<'a, 'p> {
     /// using [`layout_text`].
     pub loader: &'a SharedFontLoader<'p>,
 
+    /// Whether this layouting process handles the top-level pages.
+    pub top_level: bool,
+
     /// The style to set text with. This includes sizes and font classes
     /// which determine which font from the loaders selection is used.
-    pub style: &'a TextStyle,
+    pub text_style: &'a TextStyle,
+
+    /// The current size and margins of the top-level pages.
+    pub page_style: PageStyle,
 
     /// The spaces to layout in.
     pub spaces: LayoutSpaces,
@@ -281,6 +287,8 @@ pub enum Alignment {
 
 /// The error type for layouting.
 pub enum LayoutError {
+    /// An action is unallowed in the active context.
+    Unallowed(&'static str),
     /// There is not enough space to add an item.
     NotEnoughSpace(&'static str),
     /// There was no suitable font for the given character.
@@ -295,6 +303,7 @@ pub type LayoutResult<T> = Result<T, LayoutError>;
 error_type! {
     err: LayoutError,
     show: f => match err {
+        LayoutError::Unallowed(desc) => write!(f, "unallowed: {}", desc),
         LayoutError::NotEnoughSpace(desc) => write!(f, "not enough space: {}", desc),
         LayoutError::NoSuitableFont(c) => write!(f, "no suitable font for '{}'", c),
         LayoutError::Font(err) => write!(f, "font error: {}", err),
diff --git a/src/layout/stacked.rs b/src/layout/stacked.rs
index a7585046..a5db5638 100644
--- a/src/layout/stacked.rs
+++ b/src/layout/stacked.rs
@@ -96,9 +96,21 @@ impl StackLayouter {
     pub fn set_axes(&mut self, axes: LayoutAxes) {
         if axes != self.ctx.axes {
             self.finish_boxes();
+            self.ctx.axes = axes;
             self.usable = self.remains();
             self.dimensions = Size2D::zero();
-            self.ctx.axes = axes;
+        }
+    }
+
+    /// Update the followup space to be used by this flex layouter.
+    pub fn set_spaces(&mut self, spaces: LayoutSpaces, replace_empty: bool) {
+        if replace_empty && self.space_is_empty() {
+            self.usable = self.ctx.axes.generalize(spaces[0].usable());
+            self.active_space = 0;
+            self.ctx.spaces = spaces;
+        } else {
+            self.ctx.spaces.truncate(self.active_space + 1);
+            self.ctx.spaces.extend(spaces);
         }
     }
 
@@ -143,6 +155,10 @@ impl StackLayouter {
 
     /// Compose all cached boxes into a layout.
     fn finish_boxes(&mut self) {
+        if self.boxes.is_empty() {
+            return;
+        }
+
         let space = self.ctx.spaces[self.active_space];
         let start = space.start() + Size2D::with_y(self.merged_dimensions.y);
 
@@ -170,11 +186,6 @@ impl StackLayouter {
         self.merged_dimensions = merge_sizes(self.merged_dimensions, dimensions);
     }
 
-    /// This layouter's context.
-    pub fn ctx(&self) -> &StackContext {
-        &self.ctx
-    }
-
     /// The (generalized) usable area of the current space.
     pub fn usable(&self) -> Size2D {
         self.usable
@@ -198,6 +209,10 @@ impl StackLayouter {
         Size2D::new(self.usable.x, self.usable.y - self.dimensions.y)
     }
 
+    pub fn space_is_empty(&self) -> bool {
+        self.boxes.is_empty() && self.merged_dimensions == Size2D::zero()
+    }
+
     /// Whether this layouter is in its last space.
     pub fn in_last_space(&self) -> bool {
         self.active_space == self.ctx.spaces.len() - 1
diff --git a/src/layout/tree.rs b/src/layout/tree.rs
index 177a6308..ae6a15c8 100644
--- a/src/layout/tree.rs
+++ b/src/layout/tree.rs
@@ -1,4 +1,5 @@
 use super::*;
+use smallvec::smallvec;
 
 /// Layouts syntax trees into boxes.
 pub fn layout_tree(tree: &SyntaxTree, ctx: LayoutContext) -> LayoutResult<MultiLayout> {
@@ -19,12 +20,12 @@ 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),
+                flex_spacing: flex_spacing(&ctx.text_style),
                 spaces: ctx.spaces.clone(),
                 axes: ctx.axes,
                 shrink_to_fit: ctx.shrink_to_fit,
             }),
-            style: ctx.style.clone(),
+            style: ctx.text_style.clone(),
             ctx,
         }
     }
@@ -68,7 +69,8 @@ impl<'a, 'p> TreeLayouter<'a, 'p> {
         let (flex_spaces, stack_spaces) = self.flex.remaining()?;
 
         let ctx = |spaces| LayoutContext {
-            style: &self.style,
+            top_level: false,
+            text_style: &self.style,
             spaces: spaces,
             shrink_to_fit: true,
             .. self.ctx
@@ -107,7 +109,21 @@ impl<'a, 'p> TreeLayouter<'a, 'p> {
 
             Command::BreakParagraph => self.break_paragraph()?,
 
-            Command::SetStyle(style) => self.style = style,
+            Command::SetTextStyle(style) => self.style = style,
+            Command::SetPageStyle(style) => {
+                if !self.ctx.top_level {
+                    Err(LayoutError::Unallowed("can only set page style from top level"))?;
+                }
+
+                self.ctx.page_style = style;
+                self.flex.set_spaces(smallvec![
+                    LayoutSpace {
+                        dimensions: style.dimensions,
+                        padding: style.margins,
+                    }
+                ], true);
+            },
+
             Command::SetAxes(axes) => {
                 self.flex.set_axes(axes);
                 self.ctx.axes = axes;
diff --git a/src/lib.rs b/src/lib.rs
index d2494166..c6a21c51 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -21,7 +21,7 @@ use smallvec::smallvec;
 use toddle::query::{FontLoader, FontProvider, SharedFontLoader};
 
 use crate::func::Scope;
-use crate::layout::{layout_tree, LayoutContext, MultiLayout};
+use crate::layout::{layout_tree, MultiLayout, LayoutContext};
 use crate::layout::{LayoutAxes, AlignedAxis, Axis, Alignment};
 use crate::layout::{LayoutError, LayoutResult, LayoutSpace};
 use crate::syntax::{SyntaxTree, parse, ParseContext, ParseError, ParseResult};
@@ -98,7 +98,9 @@ impl<'p> Typesetter<'p> {
             &tree,
             LayoutContext {
                 loader: &self.loader,
-                style: &self.text_style,
+                top_level: true,
+                text_style: &self.text_style,
+                page_style: self.page_style,
                 spaces: smallvec![LayoutSpace {
                     dimensions: self.page_style.dimensions,
                     padding: self.page_style.margins,
diff --git a/src/library/mod.rs b/src/library/mod.rs
index d795d488..5fa326c8 100644
--- a/src/library/mod.rs
+++ b/src/library/mod.rs
@@ -6,6 +6,7 @@ pub_use_mod!(boxed);
 pub_use_mod!(axes);
 pub_use_mod!(spacing);
 pub_use_mod!(style);
+pub_use_mod!(page);
 
 /// Create a scope with all standard functions.
 pub fn std() -> Scope {
@@ -19,7 +20,6 @@ pub fn std() -> Scope {
     std.add::<LineBreak>("line.break");
     std.add::<ParagraphBreak>("paragraph.break");
     std.add::<PageBreak>("page.break");
-
     std.add::<HorizontalSpace>("h");
     std.add::<VerticalSpace>("v");
 
@@ -27,5 +27,8 @@ pub fn std() -> Scope {
     std.add::<Italic>("italic");
     std.add::<Monospace>("mono");
 
+    std.add::<PageSize>("page.size");
+    std.add::<PageMargins>("page.margins");
+
     std
 }
diff --git a/src/library/page.rs b/src/library/page.rs
new file mode 100644
index 00000000..4efcbea0
--- /dev/null
+++ b/src/library/page.rs
@@ -0,0 +1,79 @@
+use crate::func::prelude::*;
+
+/// `page.break`: Ends the current page.
+#[derive(Debug, PartialEq)]
+pub struct PageBreak;
+
+function! {
+    data: PageBreak,
+    parse: plain,
+    layout(_, _) { Ok(commands![FinishLayout]) }
+}
+
+/// `page.size`: Set the size of pages.
+#[derive(Debug, PartialEq)]
+pub struct PageSize {
+    width: Option<Size>,
+    height: Option<Size>,
+}
+
+function! {
+    data: PageSize,
+
+    parse(args, body, _ctx) {
+        parse!(forbidden: body);
+        Ok(PageSize {
+            width: args.get_key_opt::<ArgSize>("width")?.map(|a| a.val),
+            height: args.get_key_opt::<ArgSize>("height")?.map(|a| a.val),
+        })
+    }
+
+    layout(this, ctx) {
+        let mut style = ctx.page_style;
+
+        if let Some(width) = this.width { style.dimensions.x = width; }
+        if let Some(height) = this.height { style.dimensions.y = height; }
+
+        Ok(commands![SetPageStyle(style)])
+    }
+}
+
+/// `page.margins`: Set the margins of pages.
+#[derive(Debug, PartialEq)]
+pub struct PageMargins {
+    left: Option<Size>,
+    top: Option<Size>,
+    right: Option<Size>,
+    bottom: Option<Size>,
+}
+
+function! {
+    data: PageMargins,
+
+    parse(args, body, _ctx) {
+        parse!(forbidden: body);
+        let default = args.get_pos_opt::<ArgSize>()?;
+        let mut get = |which| {
+            args.get_key_opt::<ArgSize>(which)
+                .map(|size| size.or(default).map(|a| a.val))
+        };
+
+        Ok(PageMargins {
+            left: get("left")?,
+            top: get("top")?,
+            right: get("right")?,
+            bottom: get("bottom")?,
+        })
+    }
+
+    layout(this, ctx) {
+        let mut style = ctx.page_style;
+
+        if let Some(left) = this.left { style.margins.left = left; }
+        if let Some(top) = this.top { style.margins.top = top; }
+        if let Some(right) = this.right { style.margins.right = right; }
+        if let Some(bottom) = this.bottom { style.margins.bottom = bottom; }
+
+        Ok(commands![SetPageStyle(style)])
+    }
+}
diff --git a/src/library/spacing.rs b/src/library/spacing.rs
index afd26d80..f83f333d 100644
--- a/src/library/spacing.rs
+++ b/src/library/spacing.rs
@@ -22,16 +22,6 @@ function! {
     layout(_, _) { Ok(commands![FinishBox]) }
 }
 
-/// `page.break`: Ends the current page.
-#[derive(Debug, PartialEq)]
-pub struct PageBreak;
-
-function! {
-    data: PageBreak,
-    parse: plain,
-    layout(_, _) { Ok(commands![FinishLayout]) }
-}
-
 macro_rules! space_func {
     ($ident:ident, $doc:expr, $var:ident => $command:expr) => (
         #[doc = $doc]
@@ -57,7 +47,7 @@ macro_rules! space_func {
             layout(this, ctx) {
                 let $var = match this.0 {
                     Spacing::Absolute(s) => s,
-                    Spacing::Relative(f) => f * ctx.style.font_size,
+                    Spacing::Relative(f) => f * ctx.text_style.font_size,
                 };
 
                 Ok(commands![$command])
diff --git a/src/library/style.rs b/src/library/style.rs
index 0615c0e7..a63166cf 100644
--- a/src/library/style.rs
+++ b/src/library/style.rs
@@ -18,16 +18,16 @@ macro_rules! stylefunc {
             }
 
             layout(this, ctx) {
-                let mut style = ctx.style.clone();
+                let mut style = ctx.text_style.clone();
                 style.toggle_class(FontClass::$ident);
 
                 Ok(match &this.body {
                     Some(body) => commands![
-                        SetStyle(style),
+                        SetTextStyle(style),
                         LayoutTree(body),
-                        SetStyle(ctx.style.clone()),
+                        SetTextStyle(ctx.text_style.clone()),
                     ],
-                    None => commands![SetStyle(style)]
+                    None => commands![SetTextStyle(style)]
                 })
             }
         }
diff --git a/src/style.rs b/src/style.rs
index e2ab0937..da190b46 100644
--- a/src/style.rs
+++ b/src/style.rs
@@ -74,7 +74,7 @@ impl Default for TextStyle {
 }
 
 /// Defines the size and margins of a page.
-#[derive(Debug, Clone)]
+#[derive(Debug, Copy, Clone)]
 pub struct PageStyle {
     /// The width and height of the page.
     pub dimensions: Size2D,