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use super::*;
/// Layouts boxes flex-like.
///
/// The boxes are arranged in "lines", each line having the height of its
/// biggest box. When a box does not fit on a line anymore horizontally,
/// a new line is started.
///
/// The flex layouter does not actually compute anything until the `finish`
/// method is called. The reason for this is the flex layouter will have
/// the capability to justify its layouts, later. To find a good justification
/// it needs total information about the contents.
///
/// There are two different kinds units that can be added to a flex run:
/// Normal layouts and _glue_. _Glue_ layouts are only written if a normal
/// layout follows and a glue layout is omitted if the following layout
/// flows into a new line. A _glue_ layout is typically used for a space character
/// since it prevents a space from appearing in the beginning or end of a line.
/// However, it can be any layout.
#[derive(Debug, Clone)]
pub struct FlexLayouter {
ctx: FlexContext,
units: Vec<FlexUnit>,
stack: StackLayouter,
usable: Size,
run: FlexRun,
space: Option<Size>,
}
/// The context for flex layouting.
///
/// See [`LayoutContext`] for details about the fields.
#[derive(Debug, Clone)]
pub struct FlexContext {
pub spaces: LayoutSpaces,
pub axes: LayoutAxes,
/// The spacing between two lines of boxes.
pub flex_spacing: Size,
}
#[derive(Debug, Clone)]
enum FlexUnit {
/// A content unit to be arranged flexibly.
Boxed(Layout),
/// Space between two box units which is only present if there
/// was no flow break in between the two surrounding units.
Space(Size),
/// A forced break of the current flex run.
Break,
SetAxes(LayoutAxes),
}
#[derive(Debug, Clone)]
struct FlexRun {
content: Vec<(Size, Layout)>,
size: Size2D,
}
impl FlexLayouter {
/// Create a new flex layouter.
pub fn new(ctx: FlexContext) -> FlexLayouter {
let stack = StackLayouter::new(StackContext {
spaces: ctx.spaces,
axes: ctx.axes,
});
FlexLayouter {
ctx,
units: vec![],
stack,
usable: stack.usable().x,
run: FlexRun { content: vec![], size: Size2D::zero() },
space: None,
}
}
/// 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));
}
/// Add a forced run break.
pub fn add_break(&mut self) {
self.units.push(FlexUnit::Break);
}
/// Update the axes in use by this flex layouter.
pub fn set_axes(&self, axes: LayoutAxes) {
self.units.push(FlexUnit::SetAxes(axes));
}
/// Compute the justified layout.
///
/// The layouter is not consumed by this to prevent ownership problems
/// with borrowed layouters. The state of the layouter is not reset.
/// Therefore, it should not be further used after calling `finish`.
pub fn finish(&mut self) -> LayoutResult<MultiLayout> {
// Move the units out of the layout because otherwise, we run into
// ownership problems.
let units = std::mem::replace(&mut self.units, vec![]);
for unit in units {
match unit {
FlexUnit::Boxed(boxed) => self.layout_box(boxed)?,
FlexUnit::Space(space) => {
self.space = Some(space);
}
FlexUnit::Break => {
self.space = None;
self.finish_run()?;
},
FlexUnit::SetAxes(axes) => self.layout_set_axes(axes),
}
}
// Finish the last flex run.
self.finish_run()?;
Ok(self.stack.finish())
}
/// 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 space = self.space.unwrap_or(Size::zero());
let new_run_size = self.run.size.x + space + size.x;
if new_run_size > self.usable {
self.space = None;
while size.x > self.usable {
if self.stack.in_last_space() {
Err(LayoutError::NotEnoughSpace("cannot fix box into flex run"))?;
}
self.stack.add_break(true);
self.usable = self.stack.usable().x;
}
self.finish_run()?;
}
if let Some(space) = self.space.take() {
if self.run.size.x > Size::zero() && self.run.size.x + space <= self.usable {
self.run.size.x += space;
}
}
self.run.content.push((self.run.size.x, boxed));
self.run.size.x += size.x;
self.run.size.y = crate::size::max(self.run.size.y, size.y);
Ok(())
}
fn layout_set_axes(&mut self, axes: LayoutAxes) {
// TODO
}
/// Finish the current flex run.
fn finish_run(&mut self) -> LayoutResult<()> {
let mut actions = LayoutActionList::new();
for (x, layout) in self.run.content.drain(..) {
let position = self.ctx.axes.specialize(Size2D::with_x(x));
actions.add_layout(position, layout);
}
self.run.size.y += self.ctx.flex_spacing;
self.stack.add(Layout {
dimensions: self.ctx.axes.specialize(self.run.size),
actions: actions.into_vec(),
debug_render: false,
})?;
self.run.size = Size2D::zero();
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()
}
}
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