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|
//! Flexible and lazy layouting of boxes.
use crate::size::{Size, Size2D};
use super::*;
/// Finishes a flex layout by justifying the positions of the individual boxes.
#[derive(Debug)]
pub struct FlexLayouter {
ctx: FlexContext,
units: Vec<FlexUnit>,
actions: LayoutActionList,
dimensions: Size2D,
usable: Size2D,
cursor: Size2D,
line_content: Vec<(Size2D, Layout)>,
line_metrics: Size2D,
last_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 flex spacing between two lines of boxes.
pub flex_spacing: Size,
}
/// A unit in a flex layout.
#[derive(Debug, Clone)]
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),
}
impl FlexLayouter {
/// Create a new flex layouter.
pub fn new(ctx: FlexContext) -> FlexLayouter {
FlexLayouter {
ctx,
units: vec![],
actions: LayoutActionList::new(),
dimensions: match ctx.space.alignment {
Alignment::Left => Size2D::zero(),
Alignment::Right => Size2D::with_x(ctx.space.usable().x),
},
usable: ctx.space.usable(),
cursor: Size2D::new(ctx.space.padding.left, ctx.space.padding.top),
line_content: vec![],
line_metrics: Size2D::zero(),
last_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));
}
/// Whether this layouter contains any items.
pub fn is_empty(&self) -> bool {
self.units.is_empty()
}
/// Compute the justified layout.
pub fn finish(mut self) -> LayoutResult<Layout> {
// 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(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,
})
}
/// Layout the box.
fn boxed(&mut self, boxed: Layout) -> LayoutResult<()> {
let last_glue_x = self.last_glue.as_ref()
.map(|g| g.dimensions.x)
.unwrap_or(Size::zero());
// Move to the next line if necessary.
if self.line_metrics.x + boxed.dimensions.x + last_glue_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();
} else if let Some(glue) = self.last_glue.take() {
self.append(glue);
}
self.append(boxed);
Ok(())
}
/// Layout the glue.
fn glue(&mut self, glue: Layout) {
if let Some(glue) = self.last_glue.take() {
self.append(glue);
}
self.last_glue = Some(glue);
}
/// Append a box to the layout without checking anything.
fn append(&mut self, layout: Layout) {
let dim = layout.dimensions;
self.line_content.push((self.cursor, layout));
self.line_metrics.x += dim.x;
self.line_metrics.y = crate::size::max(self.line_metrics.y, dim.y);
self.cursor.x += dim.x;
}
/// Move to the next line.
fn newline(&mut self) {
// Move all actions into this layout and translate absolute positions.
let remaining_space = Size2D::with_x(self.ctx.space.usable().x - self.line_metrics.x);
for (cursor, layout) in self.line_content.drain(..) {
let position = match self.ctx.space.alignment {
Alignment::Left => cursor,
Alignment::Right => {
// Right align everything by shifting it right by the
// amount of space left to the right of the line.
cursor + remaining_space
},
};
self.actions.add_box(position, layout);
}
// Stretch the dimensions to at least the line width.
self.dimensions.x = crate::size::max(self.dimensions.x, self.line_metrics.x);
// If we wrote a line previously add the inter-line spacing.
if self.dimensions.y > Size::zero() {
self.dimensions.y += self.ctx.flex_spacing;
}
self.dimensions.y += self.line_metrics.y;
// Reset the cursor the left and move down by the line and the inter-line spacing.
self.cursor.x = self.ctx.space.padding.left;
self.cursor.y += self.line_metrics.y + self.ctx.flex_spacing;
// Reset the current line metrics.
self.line_metrics = Size2D::zero();
}
}
|
