hierarchy & example

Cargo.lock

@@ -4315,6 +4315,14 @@ dependencies = [
  "float-cmp",
 ]
 
+[[package]]
+name = "styling_engine"
+version = "0.1.0"
+dependencies = [
+ "eframe",
+ "env_logger",
+]
+
 [[package]]
 name = "subtle"
 version = "2.6.1"

crates/egui/src/containers/panel.rs

@@ -15,6 +15,8 @@
 //!
 //! Add your [`crate::Window`]:s after any top-level panels.
 
+use std::sync::Arc;
+
 use emath::{GuiRounding as _, Pos2};
 
 use crate::{
@@ -1027,10 +1029,12 @@ impl CentralPanel {
                 .max_rect(panel_rect)
                 .layout(Layout::top_down(Align::Min)),
         );
+        let style_stack = ui.style_stack_mut().clone();
         panel_ui.set_clip_rect(panel_rect); // If we overflow, don't do so visibly (#4475)
 
         let frame = frame.unwrap_or_else(|| Frame::central_panel(ui.style()));
         let response = frame.show(&mut panel_ui, |ui| {
+            ui.style_stack_mut().parent = Some(Arc::new(style_stack));
             ui.expand_to_include_rect(ui.max_rect()); // Expand frame to include it all
             add_contents(ui)
         });

crates/egui/src/ui.rs

@@ -7,7 +7,7 @@ use emath::GuiRounding as _;
 use epaint::mutex::RwLock;
 
 use crate::containers::menu;
-use crate::widget_style::{HasModifiers, StyleModifiers};
+use crate::widget_style::{HasModifiers, StyleModifiers, StyleStack};
 use crate::{containers::*, ecolor::*, layout::*, placer::Placer, widgets::*, *};
 // ----------------------------------------------------------------------------
 
@@ -91,8 +91,8 @@ pub struct Ui {
     /// end of a [`Ui::scope`].
     min_rect_already_remembered: bool,
 
-    /// Modifiers for style purpose
-    modifiers: StyleModifiers,
+    /// test
+    style_stack: Arc<StyleStack>,
 }
 
 /// Allow using [`Ui`] like a [`Context`].
@@ -117,7 +117,7 @@ impl Ui {
         let UiBuilder {
             id_salt,
             global_scope: _,
-            ui_stack_info,
+            mut ui_stack_info,
             layer_id,
             max_rect,
             layout,
@@ -143,6 +143,9 @@ impl Ui {
         let style = style.unwrap_or_else(|| ctx.global_style());
         let sense = sense.unwrap_or_else(Sense::hover);
 
+        // Temporary use of user tags as proof of concept
+        ui_stack_info = ui_stack_info.with_tag("root");
+
         let placer = Placer::new(max_rect, layout);
         let ui_stack = UiStack {
             id,
@@ -152,6 +155,12 @@ impl Ui {
             min_rect: placer.min_rect(),
             max_rect: placer.max_rect(),
         };
+
+        let style_stack = StyleStack {
+            modifiers: StyleModifiers::default(),
+            parent: None,
+        };
+
         let mut ui = Ui {
             id,
             unique_id: id,
@@ -165,7 +174,7 @@ impl Ui {
             stack: Arc::new(ui_stack),
             sense,
             min_rect_already_remembered: false,
-            modifiers: StyleModifiers::default(),
+            style_stack: Arc::new(style_stack),
         };
 
         if let Some(accessibility_parent) = accessibility_parent {
@@ -315,6 +324,12 @@ impl Ui {
             min_rect: placer.min_rect(),
             max_rect: placer.max_rect(),
         };
+
+        let style_stack = StyleStack {
+            modifiers: StyleModifiers::default(),
+            parent: Some(Arc::clone(&self.style_stack)),
+        };
+
         let mut child_ui = Ui {
             id: stable_id,
             unique_id,
@@ -328,7 +343,7 @@ impl Ui {
             stack: Arc::new(ui_stack),
             sense,
             min_rect_already_remembered: false,
-            modifiers: StyleModifiers::default(),
+            style_stack: Arc::new(style_stack),
         };
 
         if disabled {
@@ -3153,11 +3168,34 @@ impl Drop for Ui {
 
 impl HasModifiers for Ui {
     fn modifiers(&self) -> &StyleModifiers {
-        &self.modifiers
+        &self.style_stack.modifiers
     }
 
     fn modifiers_mut(&mut self) -> &mut StyleModifiers {
-        &mut self.modifiers
+        &mut self.style_stack_mut().modifiers
+    }
+}
+
+impl Ui {
+    /// borrow internal [`StyleStack`].
+    /// Allow the access to the modifiers of the ui's ancestors
+    ///
+    /// Example:
+    /// ```
+    /// # egui::__run_test_ui(|ui| {
+    /// // Check if the parent has the "test" modifier
+    /// ui.style_stack().parent.is_some_and(|parent| parent.modifiers.has("test"));
+    ///
+    /// // Same but shorter
+    /// ui.style_stack().parent_has("test");
+    /// # });
+    /// ```
+    pub fn style_stack(&self) -> &StyleStack {
+        &self.style_stack
+    }
+
+    pub(crate) fn style_stack_mut(&mut self) -> &mut StyleStack {
+        Arc::make_mut(&mut self.style_stack)
     }
 }
 

crates/egui/src/ui_stack.rs

@@ -201,7 +201,7 @@ impl UiTags {
 /// Note: since [`UiStack`] contains a reference to its parent, it is both a stack, and a node within
 /// that stack. Most of its methods are about the specific node, but some methods walk up the
 /// hierarchy to provide information about the entire stack.
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct UiStack {
     // stuff that `Ui::child_ui` can deal with directly
     pub id: Id,

crates/egui/src/widget_style.rs

@@ -1,3 +1,5 @@
+use std::{iter::FusedIterator, sync::Arc};
+
 use emath::Vec2;
 use epaint::{Color32, FontId, Shadow, Stroke, text::TextWrapMode};
 
@@ -203,7 +205,7 @@ impl Style {
 pub type WidgetStyleModifier = String;
 
 /// For now we use Vec for the modifiers but later we could use `SmallVev` for performance
-#[derive(Default)]
+#[derive(Debug, Default, Clone)]
 pub struct StyleModifiers {
     modifiers: Vec<WidgetStyleModifier>,
     theme: Option<Theme>,
@@ -213,15 +215,15 @@ pub struct StyleModifiers {
 impl StyleModifiers {
     /// Add multiples modifiers in one method and return the list for method chaining
     #[inline]
-    pub fn with_modifiers(mut self, classes: &[WidgetStyleModifier]) -> Self {
-        self.modifiers.append(&mut classes.to_vec());
+    pub fn with_modifiers(mut self, modifiers: &[WidgetStyleModifier]) -> Self {
+        self.modifiers.append(&mut modifiers.to_vec());
         self
     }
 
     /// Add a single modifier and return the list for method chaining
     #[inline]
-    pub fn with_modifier(mut self, class: impl Into<WidgetStyleModifier>) -> Self {
-        self.modifiers.push(class.into());
+    pub fn with_modifier(mut self, modifier: impl Into<WidgetStyleModifier>) -> Self {
+        self.modifiers.push(modifier.into());
         self
     }
 
@@ -252,6 +254,10 @@ impl StyleModifiers {
     pub fn with_state(&mut self, state: WidgetState) {
         self.state = state;
     }
+
+    pub fn list(&self) -> Vec<WidgetStyleModifier> {
+        self.modifiers.clone()
+    }
 }
 
 /// Any widgets supporting [`StyleModifiers`] must implement this trait
@@ -260,11 +266,6 @@ pub trait HasModifiers {
 
     fn modifiers_mut(&mut self) -> &mut StyleModifiers;
 
-    fn add_class(&mut self, modifier: impl Into<WidgetStyleModifier>) -> &Self {
-        self.modifiers_mut().add_if(modifier.into(), true);
-        self
-    }
-
     #[inline]
     fn with_modifier(mut self, modifier: impl Into<WidgetStyleModifier>) -> Self
     where
@@ -283,6 +284,28 @@ pub trait HasModifiers {
         self
     }
 
+    #[inline]
+    fn add_modifier(&mut self, modifier: impl Into<WidgetStyleModifier>) -> &mut Self
+    where
+        Self: Sized,
+    {
+        self.modifiers_mut().add_if(modifier.into(), true);
+        self
+    }
+
+    #[inline]
+    fn add_modifier_if(
+        &mut self,
+        modifier: impl Into<WidgetStyleModifier>,
+        condition: bool,
+    ) -> &mut Self
+    where
+        Self: Sized,
+    {
+        self.modifiers_mut().add_if(modifier.into(), condition);
+        self
+    }
+
     #[inline]
     fn theme(mut self, theme: Theme) -> Self
     where
@@ -315,3 +338,62 @@ macro_rules! add_modifiers {
         }
     };
 }
+
+#[derive(Debug, Clone)]
+pub struct StyleStack {
+    pub modifiers: StyleModifiers,
+    pub parent: Option<Arc<Self>>,
+}
+
+// these methods act on the entire stack
+impl StyleStack {
+    /// Return an iterator that walks the stack from this node to the root.
+    #[expect(clippy::iter_without_into_iter)]
+    pub fn iter(&self) -> StyleStackIterator<'_> {
+        StyleStackIterator { next: Some(self) }
+    }
+
+    /// Check if any of the ancestor has the modifiers
+    pub fn ancestors_have(&self, modifier: impl Into<WidgetStyleModifier>) -> bool {
+        let modifier = modifier.into();
+        self.iter()
+            .any(|parent| parent.modifiers.has(modifier.clone()))
+    }
+
+    /// Check if the direct parent has the modifiers
+    pub fn parent_has(&self, modifier: impl Into<WidgetStyleModifier>) -> bool {
+        if let Some(parent) = &self.parent {
+            parent.modifiers.has(modifier)
+        } else {
+            false
+        }
+    }
+
+    pub fn parent_modifiers(&self) -> Option<&StyleModifiers> {
+        self.parent.as_ref().map(|parent| &parent.modifiers)
+    }
+
+    pub fn ancestors_modifiers(&self) -> Vec<&StyleModifiers> {
+        self.iter().map(|f| &f.modifiers).collect()
+    }
+}
+
+/// Iterator that walks up a stack of `StackFrame`s.
+///
+/// See [`StyleStack::iter`].
+pub struct StyleStackIterator<'a> {
+    next: Option<&'a StyleStack>,
+}
+
+impl<'a> Iterator for StyleStackIterator<'a> {
+    type Item = &'a StyleStack;
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        let current = self.next;
+        self.next = current.and_then(|style| style.parent.as_deref());
+        current
+    }
+}
+
+impl FusedIterator for StyleStackIterator<'_> {}

crates/egui/src/widgets/checkbox.rs

@@ -24,7 +24,7 @@ pub struct Checkbox<'a> {
     checked: &'a mut bool,
     atoms: Atoms<'a>,
     indeterminate: bool,
-    modifier: StyleModifiers,
+    modifiers: StyleModifiers,
 }
 
 impl<'a> Checkbox<'a> {
@@ -33,7 +33,7 @@ impl<'a> Checkbox<'a> {
             checked,
             atoms: atoms.into_atoms(),
             indeterminate: false,
-            modifier: StyleModifiers::default(),
+            modifiers: StyleModifiers::default(),
         }
     }
 
@@ -58,7 +58,7 @@ impl Widget for Checkbox<'_> {
             checked,
             mut atoms,
             indeterminate,
-            mut modifier,
+            modifiers: mut modifier,
         } = self;
 
         // Get the widget style by reading the response from the previous pass
@@ -161,10 +161,10 @@ impl Widget for Checkbox<'_> {
 
 impl HasModifiers for Checkbox<'_> {
     fn modifiers(&self) -> &crate::widget_style::StyleModifiers {
-        &self.modifier
+        &self.modifiers
     }
 
     fn modifiers_mut(&mut self) -> &mut crate::widget_style::StyleModifiers {
-        &mut self.modifier
+        &mut self.modifiers
     }
 }

crates/egui/src/widgets/separator.rs

@@ -19,7 +19,7 @@ pub struct Separator {
     spacing: Option<f32>,
     grow: f32,
     is_horizontal_line: Option<bool>,
-    modifier: StyleModifiers,
+    modifiers: StyleModifiers,
 }
 
 impl Default for Separator {
@@ -28,7 +28,7 @@ impl Default for Separator {
             spacing: None,
             grow: 0.0,
             is_horizontal_line: None,
-            modifier: StyleModifiers::default(),
+            modifiers: StyleModifiers::default(),
         }
     }
 }
@@ -96,7 +96,7 @@ impl Widget for Separator {
             spacing,
             grow,
             is_horizontal_line,
-            mut modifier,
+            modifiers: mut modifier,
         } = self;
 
         // Get the widget style by reading the response from the previous pass
@@ -152,10 +152,10 @@ impl Widget for Separator {
 
 impl HasModifiers for Separator {
     fn modifiers(&self) -> &crate::widget_style::StyleModifiers {
-        &self.modifier
+        &self.modifiers
     }
 
     fn modifiers_mut(&mut self) -> &mut crate::widget_style::StyleModifiers {
-        &mut self.modifier
+        &mut self.modifiers
     }
 }

examples/styling_engine/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "styling_engine"
+version = "0.1.0"
+authors = ["Emil Ernerfeldt <emil.ernerfeldt@gmail.com>"]
+license = "MIT OR Apache-2.0"
+edition = "2024"
+rust-version = "1.92"
+publish = false
+
+[lints]
+workspace = true
+
+
+[dependencies]
+eframe = { workspace = true, features = [
+  "default",
+  "__screenshot", # __screenshot is so we can dump a screenshot using EFRAME_SCREENSHOT_TO
+] }
+env_logger = { workspace = true, features = ["auto-color", "humantime"] }

examples/styling_engine/README.md

@@ -0,0 +1,7 @@
+Example showing how the style engine work.
+
+```sh
+cargo run -p styling_engine
+```
+
+![](screenshot.png)

examples/styling_engine/screenshot.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:7cde6a351fbcf5a5d3b5474353c627a9c93801563880b7ff41dfa025da3c6d37
+size 8587

examples/styling_engine/src/main.rs

@@ -0,0 +1,44 @@
+#![cfg_attr(not(debug_assertions), windows_subsystem = "windows")] // hide console window on Windows in release
+#![expect(rustdoc::missing_crate_level_docs)] // it's an example
+
+use eframe::egui::{self, Button, Frame, Grid, Margin, Panel, widget_style::HasModifiers as _};
+
+fn main() -> eframe::Result {
+    env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).
+
+    let options = eframe::NativeOptions {
+        viewport: egui::ViewportBuilder::default().with_inner_size([600.0, 400.0]),
+        ..Default::default()
+    };
+
+    let mut style_code = "// future style code live editor".to_owned();
+
+    eframe::run_ui_native("My egui App", options, move |ui, _frame| {
+        // Add a modifier to this ui
+        ui.add_modifier("body");
+        ui.label("body");
+        egui::CentralPanel::default().show_inside(ui, |ui| {
+            // Add a modifier to this ui
+            ui.add_modifier("central panel");
+            ui.label("central panel");
+
+            Panel::left("style_code").show_inside(ui, |ui| {
+                ui.add_modifier("style code editor");
+                ui.label("style code editor");
+
+                ui.text_edit_multiline(&mut style_code);
+            });
+
+            Grid::new("grid").show(ui, |ui| {
+                ui.add_modifier("grid");
+
+                Frame::new().inner_margin(Margin::same(10)).show(ui, |ui| {
+                    ui.add_modifier("frame1");
+
+                    ui.add(Button::new("button1").with_modifier("button1"));
+                    ui.add(Button::new("button2").with_modifier("button2"));
+                })
+            });
+        });
+    })
+}