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|
//! Flexible and lazy layouting of boxes.
use crate::doc::LayoutAction;
use crate::size::{Size, Size2D};
use super::{BoxLayout, ActionList, LayoutSpace, LayoutResult, LayoutError};
/// A flex layout consists of a yet unarranged list of boxes.
#[derive(Debug, Clone)]
pub struct FlexLayout {
/// The sublayouts composing this layout.
pub units: Vec<FlexUnit>,
}
/// A unit in a flex layout.
#[derive(Debug, Clone)]
pub enum FlexUnit {
/// A content unit to be arranged flexibly.
Boxed(BoxLayout),
/// A unit which acts as glue between two [`FlexUnit::Boxed`] units and
/// is only present if there was no flow break in between the two surrounding boxes.
Glue(BoxLayout),
}
impl FlexLayout {
/// Create a new flex layout.
pub fn new() -> FlexLayout {
FlexLayout {
units: vec![],
}
}
/// Create a new flex layout containing just one box.
pub fn from_box(boxed: BoxLayout) -> FlexLayout {
FlexLayout {
units: vec![FlexUnit::Boxed(boxed)],
}
}
/// Add a sublayout.
pub fn add_box(&mut self, layout: BoxLayout) {
self.units.push(FlexUnit::Boxed(layout));
}
/// Add a glue layout which can be replaced by a line break.
pub fn add_glue(&mut self, glue: BoxLayout) {
self.units.push(FlexUnit::Glue(glue));
}
/// Add all sublayouts of another flex layout.
pub fn add_flexible(&mut self, layout: FlexLayout) {
self.units.extend(layout.units);
}
/// Whether this layouter contains any items.
pub fn is_empty(&self) -> bool {
self.units.is_empty()
}
/// Compute the justified layout.
pub fn finish(self, ctx: FlexContext) -> LayoutResult<BoxLayout> {
FlexFinisher::new(self, ctx).finish()
}
}
/// The context for flex layouting.
#[derive(Debug, Copy, Clone)]
pub struct FlexContext {
/// The space to layout the boxes in.
pub space: LayoutSpace,
/// The flex spacing between two lines of boxes.
pub flex_spacing: Size,
}
/// Finishes a flex layout by justifying the positions of the individual boxes.
#[derive(Debug)]
struct FlexFinisher {
units: Vec<FlexUnit>,
ctx: FlexContext,
actions: ActionList,
dimensions: Size2D,
usable: Size2D,
cursor: Size2D,
line: Size2D,
}
impl FlexFinisher {
/// Create the finisher from the layout.
fn new(layout: FlexLayout, ctx: FlexContext) -> FlexFinisher {
let space = ctx.space;
FlexFinisher {
units: layout.units,
ctx,
actions: ActionList::new(),
dimensions: Size2D::zero(),
usable: space.usable(),
cursor: Size2D::new(space.padding.left, space.padding.top),
line: Size2D::zero(),
}
}
/// Finish the flex layout into the justified box layout.
fn finish(mut self) -> LayoutResult<BoxLayout> {
// Move the units out of the layout.
let units = self.units;
self.units = vec![];
// Arrange the units.
for unit in units {
match unit {
FlexUnit::Boxed(boxed) => self.boxed(boxed)?,
FlexUnit::Glue(glue) => self.glue(glue),
}
}
// Flush everything to get the correct dimensions.
self.newline();
Ok(BoxLayout {
dimensions: if self.ctx.space.shrink_to_fit {
self.dimensions.padded(self.ctx.space.padding)
} else {
self.ctx.space.dimensions
},
actions: self.actions.into_vec(),
})
}
/// Layout the box.
fn boxed(&mut self, boxed: BoxLayout) -> LayoutResult<()> {
// Move to the next line if necessary.
if self.line.x + boxed.dimensions.x > self.usable.x {
// If it still does not fit, we stand no chance.
if boxed.dimensions.x > self.usable.x {
return Err(LayoutError::NotEnoughSpace);
}
self.newline();
}
self.append(boxed);
Ok(())
}
/// Layout the glue.
fn glue(&mut self, glue: BoxLayout) {
// Only add the glue if it fits on the line, otherwise move to the next line.
if self.line.x + glue.dimensions.x > self.usable.x {
self.newline();
} else {
self.append(glue);
}
}
/// Append a box to the layout without checking anything.
fn append(&mut self, layout: BoxLayout) {
// Move all actions into this layout and translate absolute positions.
self.actions.reset_origin();
self.actions.add(LayoutAction::MoveAbsolute(self.cursor));
self.actions.set_origin(self.cursor);
self.actions.extend(layout.actions);
// Adjust the sizes.
self.line.x += layout.dimensions.x;
self.line.y = crate::size::max(self.line.y, layout.dimensions.y);
self.cursor.x += layout.dimensions.x;
}
/// Move to the next line.
fn newline(&mut self) {
self.dimensions.x = crate::size::max(self.dimensions.x, self.line.x);
if self.dimensions.y > Size::zero() {
self.dimensions.y += self.ctx.flex_spacing;
}
self.dimensions.y += self.line.y;
self.cursor.x = self.ctx.space.padding.left;
self.cursor.y += self.line.y + self.ctx.flex_spacing;
self.line = Size2D::zero();
}
}
|
