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use super::*;
/// Flex-layouting of boxes.
///
/// 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.
pub struct FlexLayouter {
ctx: FlexContext,
units: Vec<FlexUnit>,
actions: LayoutActionList,
usable: Size2D,
dimensions: Size2D,
cursor: Size2D,
run: FlexRun,
next_glue: Option<Layout>,
}
/// The context for flex layouting.
#[derive(Debug, Copy, Clone)]
pub struct FlexContext {
/// The space to layout the boxes in.
pub space: LayoutSpace,
/// The spacing between two lines of boxes.
pub flex_spacing: Size,
}
enum FlexUnit {
/// A content unit to be arranged flexibly.
Boxed(Layout),
/// 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(Layout),
}
struct FlexRun {
content: Vec<(Size2D, Layout)>,
size: Size2D,
}
impl FlexLayouter {
/// Create a new flex layouter.
pub fn new(ctx: FlexContext) -> FlexLayouter {
FlexLayouter {
ctx,
units: vec![],
actions: LayoutActionList::new(),
usable: ctx.space.usable(),
dimensions: match ctx.space.alignment {
Alignment::Left => Size2D::zero(),
Alignment::Right => Size2D::with_x(ctx.space.usable().x),
},
cursor: Size2D::new(ctx.space.padding.left, ctx.space.padding.top),
run: FlexRun::new(),
next_glue: None,
}
}
/// Get a reference to 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 a glue layout which can be replaced by a line break.
pub fn add_glue(&mut self, glue: Layout) {
self.units.push(FlexUnit::Glue(glue));
}
/// Compute the justified layout.
pub fn finish(mut self) -> LayoutResult<Layout> {
// Move the units out of the layout because otherwise, we run into
// ownership problems.
let units = self.units;
self.units = Vec::new();
for unit in units {
match unit {
FlexUnit::Boxed(boxed) => self.layout_box(boxed)?,
FlexUnit::Glue(glue) => self.layout_glue(glue),
}
}
// Finish the last flex run.
self.finish_flex_run();
Ok(Layout {
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(),
debug_render: true,
})
}
/// Whether this layouter contains any items.
pub fn is_empty(&self) -> bool {
self.units.is_empty()
}
fn layout_box(&mut self, boxed: Layout) -> LayoutResult<()> {
let next_glue_width = self
.next_glue
.as_ref()
.map(|g| g.dimensions.x)
.unwrap_or(Size::zero());
let new_line_width = self.run.size.x + next_glue_width + boxed.dimensions.x;
if self.overflows(new_line_width) {
// If the box does not even fit on its own line, then
// we can't do anything.
if self.overflows(boxed.dimensions.x) {
return Err(LayoutError::NotEnoughSpace);
}
self.finish_flex_run();
} else {
// Only add the glue if we did not move to a new line.
self.flush_glue();
}
self.add_to_flex_run(boxed);
Ok(())
}
fn layout_glue(&mut self, glue: Layout) {
self.flush_glue();
self.next_glue = Some(glue);
}
fn flush_glue(&mut self) {
if let Some(glue) = self.next_glue.take() {
self.add_to_flex_run(glue);
}
}
fn add_to_flex_run(&mut self, layout: Layout) {
let position = self.cursor;
self.cursor.x += layout.dimensions.x;
self.run.size.x += layout.dimensions.x;
self.run.size.y = crate::size::max(self.run.size.y, layout.dimensions.y);
self.run.content.push((position, layout));
}
fn finish_flex_run(&mut self) {
// Add all layouts from the current flex run at the correct positions.
match self.ctx.space.alignment {
Alignment::Left => {
for (position, layout) in self.run.content.drain(..) {
self.actions.add_layout(position, layout);
}
}
Alignment::Right => {
let extra_space = Size2D::with_x(self.usable.x - self.run.size.x);
for (position, layout) in self.run.content.drain(..) {
self.actions.add_layout(position + extra_space, layout);
}
}
}
self.dimensions.x = crate::size::max(self.dimensions.x, self.run.size.x);
self.dimensions.y += self.ctx.flex_spacing;
self.dimensions.y += self.run.size.y;
self.cursor.x = self.ctx.space.padding.left;
self.cursor.y += self.run.size.y + self.ctx.flex_spacing;
self.run.size = Size2D::zero();
}
fn overflows(&self, line: Size) -> bool {
line > self.usable.x
}
}
impl FlexRun {
fn new() -> FlexRun {
FlexRun {
content: vec![],
size: Size2D::zero()
}
}
}
|
