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Add AtomLayout::direction (#8221)

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* To be merged after #8219 

Adds support for vertical atom layout. Together with #8219 this
basically creates a minimal flex layout engine
This commit is contained in:
Lucas Meurer
2026-06-24 13:56:54 +02:00
committed by GitHub
parent 3c11c7b1b1
commit 080ce81c8b
3 changed files with 181 additions and 48 deletions
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174
crates/egui/src/atomics/atom_layout.rs
View File

@@ -1,6 +1,6 @@
use crate::{
AtomKind, Atoms, FontSelection, Frame, Id, Image, IntoAtoms, Response, Sense, SizedAtom,
SizedAtomKind, Stroke, Ui, Widget, text_selection::LabelSelectionState,
AtomKind, Atoms, Direction, FontSelection, Frame, Id, Image, IntoAtoms, Response, Sense,
SizedAtom, SizedAtomKind, Stroke, Ui, Widget, text_selection::LabelSelectionState,
};
use emath::{Align2, GuiRounding as _, NumExt as _, Rect, Vec2};
use epaint::text::TextWrapMode;
@@ -9,6 +9,34 @@ use smallvec::SmallVec;
use std::ops::{Deref, DerefMut};
use std::sync::Arc;
/// The `(main, cross)` axis indices for `direction`, for indexing a [`Vec2`] (0 = x, 1 = y).
#[inline]
fn main_cross_axis(direction: Direction) -> (usize, usize) {
let main = usize::from(!direction.is_horizontal());
(main, 1 - main)
}
/// Build a [`Vec2`] from `main`/`cross` components for `direction`.
#[inline]
fn main_cross_vec(direction: Direction, main: f32, cross: f32) -> Vec2 {
if direction.is_horizontal() {
Vec2::new(main, cross)
} else {
Vec2::new(cross, main)
}
}
/// Build a cell [`Rect`] spanning `aligned_rect` fully on the cross axis and `[min_main, max_main]`
/// along the main axis.
#[inline]
fn main_cross_rect(direction: Direction, aligned_rect: Rect, min_main: f32, max_main: f32) -> Rect {
if direction.is_horizontal() {
Rect::from_x_y_ranges(min_main..=max_main, aligned_rect.y_range())
} else {
Rect::from_x_y_ranges(aligned_rect.x_range(), min_main..=max_main)
}
}
/// Intra-widget layout utility.
///
/// Used to lay out and paint [`crate::Atom`]s.
@@ -30,7 +58,7 @@ use std::sync::Arc;
/// [`AllocatedAtomLayout`] for interaction styling.
#[derive(Clone)]
pub struct AtomLayout<'a> {
id: Option<Id>,
pub(crate) id: Option<Id>,
pub atoms: Atoms<'a>,
gap: Option<f32>,
pub(crate) frame: Frame,
@@ -42,6 +70,7 @@ pub struct AtomLayout<'a> {
max_size: Vec2,
wrap_mode: Option<TextWrapMode>,
align2: Option<Align2>,
direction: Direction,
}
impl Default for AtomLayout<'_> {
@@ -65,6 +94,7 @@ impl<'a> AtomLayout<'a> {
max_size: Vec2::INFINITY,
wrap_mode: None,
align2: None,
direction: Direction::LeftToRight,
}
}
@@ -187,6 +217,20 @@ impl<'a> AtomLayout<'a> {
self
}
/// Set the [`Direction`] the [`crate::Atom`]s are laid out along.
///
/// The default is [`Direction::LeftToRight`] (a horizontal row). Use
/// [`Direction::TopDown`] (or [`Direction::BottomUp`]) to stack atoms vertically.
///
/// The main axis (the direction) is where `grow`/`shrink` and the gap apply; the cross axis
/// is sized to the largest atom. [`Self::align2`] positions the whole block within the
/// allocated [`Rect`].
#[inline]
pub fn direction(mut self, direction: Direction) -> Self {
self.direction = direction;
self
}
/// [`AtomLayout::allocate`] and [`AllocatedAtomLayout::paint`] in one go.
pub fn show(self, ui: &mut Ui) -> AtomLayoutResponse {
self.allocate(ui).paint(ui)
@@ -217,6 +261,7 @@ impl<'a> AtomLayout<'a> {
wrap_mode,
align2,
fallback_font,
direction,
} = self;
let fallback_font = fallback_font.unwrap_or_default();
@@ -258,23 +303,34 @@ impl<'a> AtomLayout<'a> {
// max_size has no effect in justified layouts. If we'd limit the available size here,
// the content would be sized differently than the frame which would look weird.
// This only applies along the main axis (the direction we lay atoms out along).
if direction.is_horizontal() {
if ui.layout().horizontal_justify() {
max_size.x = f32::INFINITY;
}
} else if ui.layout().vertical_justify() {
max_size.y = f32::INFINITY;
}
let available_size = available_size.at_most(max_size).at_least(min_size);
// The size available for the content
let available_inner_size = available_size - frame.total_margin().sum();
let mut inner_width = 0.0;
// We work in main/cross axis terms so the same code handles horizontal and vertical
// layouts. For a horizontal `direction`, main = x and cross = y; for vertical it's
// swapped. `grow`/`shrink`/`gap` apply along the main axis; the cross axis is sized to
// the largest atom. `main_axis`/`cross_axis` index into a `Vec2` (0 = x, 1 = y).
let (main_axis, cross_axis) = main_cross_axis(direction);
// intrinsic width / height is the ideal size of the widget, e.g. the size where the
let mut inner_main = 0.0;
// intrinsic main / cross is the ideal size of the widget, e.g. the size where the
// text is not wrapped. Used to set Response::intrinsic_size.
let mut intrinsic_width = 0.0;
let mut intrinsic_height = 0.0;
let mut intrinsic_main = 0.0;
let mut intrinsic_cross: f32 = 0.0;
let mut height: f32 = 0.0;
let mut cross_size: f32 = 0.0;
let mut sized_items = Vec::new();
@@ -288,8 +344,8 @@ impl<'a> AtomLayout<'a> {
if atoms.len() > 1 {
let gap_space = gap * (atoms.len() as f32 - 1.0);
inner_width += gap_space;
intrinsic_width += gap_space;
inner_main += gap_space;
intrinsic_main += gap_space;
}
for (idx, item) in atoms.into_iter().enumerate() {
@@ -314,19 +370,22 @@ impl<'a> AtomLayout<'a> {
);
let size = sized.size;
inner_width += size.x;
intrinsic_width += sized.intrinsic_size.x;
inner_main += size[main_axis];
intrinsic_main += sized.intrinsic_size[main_axis];
height = height.at_least(size.y);
intrinsic_height = intrinsic_height.at_least(sized.intrinsic_size.y);
cross_size = cross_size.at_least(size[cross_axis]);
intrinsic_cross = intrinsic_cross.at_least(sized.intrinsic_size[cross_axis]);
sized_items.push(sized);
}
if let Some((index, item)) = shrink_item {
// The `shrink` item gets the remaining space
let available_size_for_shrink_item =
Vec2::new(available_inner_size.x - inner_width, available_inner_size.y);
// The `shrink` item gets the remaining space along the main axis.
let available_size_for_shrink_item = main_cross_vec(
direction,
available_inner_size[main_axis] - inner_main,
available_inner_size[cross_axis],
);
let sized = item.into_sized(
ui,
@@ -336,20 +395,21 @@ impl<'a> AtomLayout<'a> {
);
let size = sized.size;
inner_width += size.x;
intrinsic_width += sized.intrinsic_size.x;
inner_main += size[main_axis];
intrinsic_main += sized.intrinsic_size[main_axis];
height = height.at_least(size.y);
intrinsic_height = intrinsic_height.at_least(sized.intrinsic_size.y);
cross_size = cross_size.at_least(size[cross_axis]);
intrinsic_cross = intrinsic_cross.at_least(sized.intrinsic_size[cross_axis]);
sized_items.insert(index, sized);
}
let margin = frame.total_margin();
let inner_size = Vec2::new(inner_width, height);
let inner_size = main_cross_vec(direction, inner_main, cross_size);
let outer_size = (inner_size + margin.sum()).at_least(min_size);
let intrinsic_size =
(Vec2::new(intrinsic_width, intrinsic_height) + margin.sum()).at_least(min_size);
let intrinsic_size = (main_cross_vec(direction, intrinsic_main, intrinsic_cross)
+ margin.sum())
.at_least(min_size);
SizedAtomLayout {
sized_atoms: sized_items,
@@ -363,6 +423,7 @@ impl<'a> AtomLayout<'a> {
inner_size,
align2,
gap,
direction,
selectable,
}
}
@@ -423,6 +484,10 @@ pub struct SizedAtomLayout<'a> {
/// The gap between each [`crate::Atom`]
gap: f32,
/// The axis the atoms are laid out along. The main axis carries `grow`/`shrink`/`gap`.
direction: Direction,
selectable: bool,
}
@@ -519,13 +584,14 @@ impl<'atom> SizedAtomLayout<'atom> {
/// becomes the base of the returned [`AtomLayoutResponse`].
pub fn paint_at(self, ui: &Ui, rect: Rect, response: Response) -> AtomLayoutResponse {
let Self {
sized_atoms,
mut sized_atoms,
frame,
fallback_text_color,
grow_count,
inner_size,
align2,
gap,
direction,
selectable,
..
} = self;
@@ -534,17 +600,32 @@ impl<'atom> SizedAtomLayout<'atom> {
ui.painter().add(frame.paint(inner_rect));
let width_to_fill = inner_rect.width();
let extra_space = f32::max(width_to_fill - inner_size.x, 0.0);
let grow_width = f32::max(extra_space / grow_count as f32, 0.0).floor_ui();
let (main_axis, cross_axis) = main_cross_axis(direction);
let aligned_rect = if grow_count > 0 {
align2.align_size_within_rect(Vec2::new(width_to_fill, inner_size.y), inner_rect)
// We position atoms along the main axis (the `direction`) and span the cross axis.
let main_to_fill = inner_rect.size()[main_axis];
let inner_main = inner_size[main_axis];
let extra_space = f32::max(main_to_fill - inner_main, 0.0);
let grow_main = f32::max(extra_space / grow_count as f32, 0.0).floor_ui();
// When something grows, the block fills the available main extent; otherwise it's the
// content's inner size. `align2` then positions the block within `inner_rect`.
let block_main = if grow_count > 0 {
main_to_fill
} else {
align2.align_size_within_rect(inner_size, inner_rect)
inner_main
};
let block_size = main_cross_vec(direction, block_main, inner_size[cross_axis]);
let aligned_rect = align2.align_size_within_rect(block_size, inner_rect);
let mut cursor = aligned_rect.left();
// For reversed directions the first atom sits at the far end, so we lay them out in
// reverse and otherwise share the same forward cursor logic.
if matches!(direction, Direction::RightToLeft | Direction::BottomUp) {
sized_atoms.reverse();
}
// The cursor walks the main axis from the start (left/top) of the aligned block.
let mut cursor = aligned_rect.min.to_vec2()[main_axis];
let mut response = AtomLayoutResponse::empty(response);
@@ -552,20 +633,21 @@ impl<'atom> SizedAtomLayout<'atom> {
let size = sized.size;
// TODO(lucasmerlin): This is not ideal, since this might lead to accumulated rounding errors
// https://github.com/emilk/egui/pull/5830#discussion_r2079627864
let growth = if sized.is_grow() { grow_width } else { 0.0 };
let growth = if sized.is_grow() { grow_main } else { 0.0 };
let frame = aligned_rect
.with_min_x(cursor)
.with_max_x(cursor + size.x + growth);
cursor = frame.right() + gap;
let rect = sized.align.align_size_within_rect(size, frame);
let atom_main = size[main_axis] + growth;
// The cell spans the cross axis fully and `atom_main` along the main axis.
let cell = main_cross_rect(direction, aligned_rect, cursor, cursor + atom_main);
cursor += atom_main + gap;
let item_rect = sized.align.align_size_within_rect(size, cell);
if let Some(id) = sized.id {
debug_assert!(
!response.custom_rects.iter().any(|(i, _)| *i == id),
"Duplicate custom id"
);
response.custom_rects.push((id, rect));
response.custom_rects.push((id, item_rect));
}
match sized.kind {
@@ -577,23 +659,25 @@ impl<'atom> SizedAtomLayout<'atom> {
LabelSelectionState::label_text_selection(
ui,
&response.response,
rect.min,
item_rect.min,
galley,
fallback_text_color,
Stroke::NONE,
);
} else {
ui.painter().galley(rect.min, galley, fallback_text_color);
ui.painter()
.galley(item_rect.min, galley, fallback_text_color);
}
}
SizedAtomKind::Image { image, size: _ } => {
image.paint_at(ui, rect);
image.paint_at(ui, item_rect);
}
SizedAtomKind::Empty { .. } => {}
SizedAtomKind::Layout(layout) => {
// TODO(lucasmerlin): Add some kind of justify flag to AtomLayout
let layout_response = ui.interact(frame, layout.id, layout.sense);
layout.paint_at(ui, frame, layout_response);
// TODO(lucasmerlin): Add some kind of justify flag, right now nested atoms are always
// shown fully stretched.
let layout_response = ui.interact(cell, layout.id, layout.sense);
layout.paint_at(ui, cell, layout_response);
}
}
}

3
tests/egui_tests/tests/snapshots/atom_layout_nesting.png Normal file
View File

@@ -0,0 +1,3 @@
version https://git-lfs.github.com/spec/v1
oid sha256:e43b410ab0a06b40da5ad9c7fd105d11201d44a3afd63fd213429cc39013c0d4
size 6964

48
tests/egui_tests/tests/test_atoms.rs
View File

@@ -1,4 +1,6 @@
use egui::{Align, AtomExt as _, Button, Layout, TextWrapMode, Ui, Vec2};
use egui::{
Align, Atom, AtomExt as _, AtomLayout, Button, Direction, Frame, Layout, TextWrapMode, Ui, Vec2,
};
use egui_kittest::{HarnessBuilder, SnapshotResult, SnapshotResults};
#[test]
@@ -120,6 +122,50 @@ fn test_button_shortcut_text() {
harness.snapshot("button_shortcut");
}
/// Test atom nesting and [`egui::AtomLayout::direction`].
#[test]
fn test_atom_layout_nesting_and_direction() {
let mut harness = HarnessBuilder::default().build_ui(|ui| {
let style = ui.style();
let canvas_frame = Frame::canvas(style);
let button_frame = style
.button_style(
&egui::widget_style::Classes::default(),
egui::widget_style::WidgetState::Inactive,
)
.frame;
let row = |direction: Direction| {
Atom::layout(
AtomLayout::new(("one", "two", "three"))
.direction(direction)
.frame(button_frame),
)
};
AtomLayout::new((
Atom::layout(
AtomLayout::new((
row(Direction::LeftToRight).atom_grow(true),
row(Direction::RightToLeft).atom_grow(true),
))
.direction(Direction::TopDown),
)
.atom_grow(true),
row(Direction::TopDown),
row(Direction::BottomUp),
))
.direction(Direction::LeftToRight)
.frame(canvas_frame)
.show(ui);
});
harness.fit_contents();
harness.snapshot("atom_layout_nesting");
}
/// Tests the spacing between galleys.
/// All of these should look the same.
#[test]