teksilo_core/widget/layout_context.rs
1// SPDX-License-Identifier: MPL-2.0
2// SPDX-FileCopyrightText: 2026 FernTech
3
4use crate::widget_id::WidgetId;
5
6use super::LayoutResponse;
7
8/// The main (distribution) axis of the linear stack currently negotiating a
9/// child's layout, if any. Set by `HStack`/`VStack` while they query children
10/// so an orientation-agnostic flexible child (notably `Spacer`) can place its
11/// minimum length on the *main* axis only and report `0` on the cross axis —
12/// otherwise it imposes a spurious cross-axis floor on the stack. `None` when
13/// the parent is not a linear stack (or in test contexts).
14#[derive(Debug, Clone, Copy, PartialEq, Eq)]
15pub enum StackAxis {
16 Horizontal,
17 Vertical,
18}
19
20/// Context available during layout.
21pub struct LayoutContext<'a> {
22 /// The enclosing linear stack's main axis, when a stack is querying this
23 /// child (see [`StackAxis`]). `None` otherwise.
24 pub stack_main_axis: Option<StackAxis>,
25 pub theme: &'a crate::styles::Theme,
26 pub layout_direction: crate::environment::LayoutDirection,
27 /// Host window HiDPI device scale (physical px per logical px). The layout
28 /// pass is otherwise fully logical, and the renderer applies this scale at
29 /// the vertex stage — so **ordinary widgets must ignore this**. It exists
30 /// only as the escape hatch for widgets that bridge to a device-pixel OS
31 /// resource (e.g. a `WebView` sizing its native subview, which on some
32 /// toolkits — WebKitGTK on X11 — ignores fractional scaling and needs
33 /// device pixels). 1.0 in headless / test contexts.
34 pub scale_factor: f32,
35 /// Combined user×OS text-scale factor (`1.0` = 100 %). Distinct from
36 /// `scale_factor` (HiDPI device pixels): this is the *logical* accessibility
37 /// magnification. Widgets that size text from `Theme.typography` already
38 /// scale via the effective theme and should ignore this; it exists for
39 /// widgets that size from another source (`IconWidget`, the rich-text engine
40 /// default size, scene text) and need the raw factor. `1.0` in test contexts.
41 pub text_scale: f32,
42 /// Text backend for accurate text measurement during layout.
43 pub text_backend: Option<&'a std::rc::Rc<std::cell::RefCell<dyn teksilo_canvas::TextBackend>>>,
44 /// Arena reference for querying child widget sizes.
45 pub(crate) arena: Option<&'a crate::arena::WidgetArena>,
46 /// Optional bundle of read-only tree state (focus, shortcuts,
47 /// overlays). Carried through layout for debug-tooling consumers
48 /// like the inspector's Focus / Shortcuts / Overlays tabs. `None`
49 /// in test contexts.
50 pub(crate) extras: Option<LayoutExtras<'a>>,
51}
52
53/// Read-only handles to tree-level state that some widgets (notably
54/// the debug inspector) want to query from `layout_response`. Threaded
55/// through the recursive layout pass alongside the arena.
56#[derive(Clone, Copy)]
57pub(crate) struct LayoutExtras<'a> {
58 pub focused: Option<WidgetId>,
59 pub shortcut_registry: Option<&'a crate::shortcut::ShortcutRegistry>,
60 pub overlay_manager: Option<&'a crate::overlay::OverlayManager>,
61}
62
63impl<'a> LayoutContext<'a> {
64 /// Create a LayoutContext for testing (no arena access).
65 pub fn for_testing(theme: &'a crate::styles::Theme) -> Self {
66 Self {
67 theme,
68 layout_direction: crate::environment::LayoutDirection::LeftToRight,
69 scale_factor: 1.0,
70 text_scale: 1.0,
71 text_backend: None,
72 arena: None,
73 extras: None,
74 stack_main_axis: None,
75 }
76 }
77
78 /// The enclosing linear stack's main axis, if a stack is currently
79 /// querying this child. See [`StackAxis`].
80 pub fn stack_main_axis(&self) -> Option<StackAxis> {
81 self.stack_main_axis
82 }
83
84 /// Derive a context that advertises `axis` as the enclosing stack's main
85 /// axis. Used by `HStack`/`VStack` when querying children so a `Spacer`
86 /// (and any other orientation-agnostic flexible leaf) can size correctly
87 /// per axis. All other fields are shared with `self`.
88 pub fn with_stack_main_axis(&self, axis: StackAxis) -> LayoutContext<'a> {
89 LayoutContext {
90 stack_main_axis: Some(axis),
91 ..*self
92 }
93 }
94
95 /// The currently focused widget id, if any. Returns `None` when
96 /// the layout pass is unrelated to a tree (test contexts).
97 pub fn focused(&self) -> Option<WidgetId> {
98 self.extras.as_ref().and_then(|e| e.focused)
99 }
100
101 /// Borrow the tree's shortcut registry. Returns `None` outside a
102 /// real layout pass. Intended for read-only inspection by the
103 /// debug inspector.
104 pub fn shortcut_registry(&self) -> Option<&crate::shortcut::ShortcutRegistry> {
105 self.extras.as_ref().and_then(|e| e.shortcut_registry)
106 }
107
108 /// Borrow the tree's overlay manager. Returns `None` outside a
109 /// real layout pass. Intended for read-only inspection by the
110 /// debug inspector.
111 pub fn overlay_manager(&self) -> Option<&crate::overlay::OverlayManager> {
112 self.extras.as_ref().and_then(|e| e.overlay_manager)
113 }
114
115 /// Query a child widget's full layout response (wanted size + flex weight).
116 /// Returns None if the child doesn't exist, is dormant, or the arena is not available.
117 pub fn child_layout_response(
118 &self,
119 child_id: WidgetId,
120 proposal: teksilo_canvas::SizeProposal,
121 ) -> Option<LayoutResponse> {
122 // Routed through the arena's per-pass memoization cache so the
123 // main-then-cross queries that height-for-width negotiation issues do
124 // not recompute the same `(child, proposal)` repeatedly. The cache
125 // handles the active-state check and the `cacheable_layout()` opt-out.
126 let arena = self.arena?;
127 arena.cached_layout_response(child_id, proposal, self)
128 }
129
130 /// Measure a widget's intrinsic size for `proposal`, **regardless of
131 /// activation** — works even for dormant/collapsed widgets (and their
132 /// dormant subtrees), unlike [`child_size`](Self::child_size) /
133 /// [`child_layout_response`](Self::child_layout_response), which return
134 /// `None` for inactive widgets.
135 ///
136 /// Intended for adaptive layouts that hide some children but still need
137 /// their size to decide when to reveal them — e.g. an overflow `Toolbar`
138 /// collapsing actions into a chevron menu. Runs uncached and re-entrant-
139 /// safe; calls `layout_response`, which must be idempotent.
140 pub fn measure_intrinsic(
141 &self,
142 id: WidgetId,
143 proposal: teksilo_canvas::SizeProposal,
144 ) -> Option<teksilo_canvas::Size> {
145 self.arena?.measure_intrinsic(id, proposal, self)
146 }
147
148 /// Query a child widget's wanted size only (drops the flex weight).
149 /// Convenience over [`child_layout_response`](Self::child_layout_response).
150 pub fn child_size(
151 &self,
152 child_id: WidgetId,
153 proposal: teksilo_canvas::SizeProposal,
154 ) -> Option<teksilo_canvas::Size> {
155 self.child_layout_response(child_id, proposal)
156 .map(|r| r.size)
157 }
158
159 /// Query the laid-out bounds of any active widget. Returns `None`
160 /// when the arena is not available (test contexts) — otherwise
161 /// returns the widget's current bounds (`Rect::ZERO` if unknown).
162 /// Useful for inspector-style widgets that need to mirror another
163 /// widget's geometry into a `Signal` during the layout pass.
164 pub fn widget_bounds(&self, id: WidgetId) -> Option<teksilo_canvas::Rect> {
165 let arena = self.arena?;
166 if !arena.is_active(id) {
167 return None;
168 }
169 Some(arena.bounds(id))
170 }
171
172 /// Hit-test the active widget tree at `point` and return the
173 /// deepest widget under it. Honors `event_pass_through`. The
174 /// `exclude` argument lets the caller skip a specific subtree
175 /// (e.g. the inspector's picker overlay so it doesn't pick
176 /// itself). Returns `None` outside layout (no arena available).
177 pub fn widget_at_point(
178 &self,
179 point: teksilo_canvas::Point,
180 exclude: Option<WidgetId>,
181 ) -> Option<WidgetId> {
182 let arena = self.arena?;
183 arena.hit_test_at(point, exclude)
184 }
185
186 /// Borrow the underlying arena. Returns `None` outside a layout
187 /// pass (test contexts). Intended for read-only introspection by
188 /// debug tooling (the inspector's tree view) — use the typed
189 /// accessors above when possible.
190 pub fn arena(&self) -> Option<&crate::arena::WidgetArena> {
191 self.arena
192 }
193
194 /// Query a child's per-widget alignment override, if any.
195 pub fn child_alignment(&self, child_id: WidgetId) -> Option<teksilo_tokens::Alignment> {
196 let arena = self.arena?;
197 arena.alignment_override(child_id)
198 }
199
200 /// Whether the layout direction is right-to-left.
201 pub fn is_rtl(&self) -> bool {
202 self.layout_direction == crate::environment::LayoutDirection::RightToLeft
203 }
204}