Make dark and light style configurable in Options

crates/egui/src/context.rs

@@ -411,6 +411,8 @@ impl ContextImpl {
         let is_outermost_viewport = self.viewport_stack.is_empty(); // not necessarily root, just outermost immediate viewport
         self.viewport_stack.push(ids);
 
+        self.update_theme_mut(&new_raw_input);
+
         self.begin_frame_repaint_logic(viewport_id);
 
         let viewport = self.viewports.entry(viewport_id).or_default();
@@ -469,7 +471,13 @@ impl ContextImpl {
             });
 
             viewport.hits = if let Some(pos) = viewport.input.pointer.interact_pos() {
-                let interact_radius = self.memory.options.style.interaction.interact_radius;
+                let interact_radius = self
+                    .memory
+                    .options
+                    .style
+                    .active()
+                    .interaction
+                    .interact_radius;
 
                 crate::hit_test::hit_test(
                     &viewport.widgets_prev_frame,
@@ -565,12 +573,16 @@ impl ContextImpl {
             crate::profile_scope!("preload_font_glyphs");
             // Preload the most common characters for the most common fonts.
             // This is not very important to do, but may save a few GPU operations.
-            for font_id in self.memory.options.style.text_styles.values() {
+            for font_id in self.memory.options.style.active().text_styles.values() {
                 fonts.lock().fonts.font(font_id).preload_common_characters();
             }
         }
     }
 
+    fn update_theme_mut(&mut self, new_raw_input: &RawInput) {
+        self.memory.options.style.update(new_raw_input.system_theme);
+    }
+
     #[cfg(feature = "accesskit")]
     fn accesskit_node_builder(&mut self, id: Id) -> &mut accesskit::NodeBuilder {
         let state = self
@@ -1215,7 +1227,14 @@ impl Context {
     pub fn register_widget_info(&self, id: Id, make_info: impl Fn() -> crate::WidgetInfo) {
         #[cfg(debug_assertions)]
         self.write(|ctx| {
-            if ctx.memory.options.style.debug.show_interactive_widgets {
+            if ctx
+                .memory
+                .options
+                .style
+                .active()
+                .debug
+                .show_interactive_widgets
+            {
                 ctx.viewport().widgets_this_frame.set_info(id, make_info());
             }
         });
@@ -1574,7 +1593,7 @@ impl Context {
 
     /// The [`Style`] used by all subsequent windows, panels etc.
     pub fn style(&self) -> Arc<Style> {
-        self.options(|opt| opt.style.clone())
+        self.options(|opt| opt.style.active().clone())
     }
 
     /// Mutate the [`Style`] used by all subsequent windows, panels etc.
@@ -1587,7 +1606,7 @@ impl Context {
     /// });
     /// ```
     pub fn style_mut(&self, mutate_style: impl FnOnce(&mut Style)) {
-        self.options_mut(|opt| mutate_style(std::sync::Arc::make_mut(&mut opt.style)));
+        self.options_mut(|opt| mutate_style(opt.style.active_mut()));
     }
 
     /// The [`Style`] used by all new windows, panels etc.
@@ -1596,7 +1615,7 @@ impl Context {
     ///
     /// You can use [`Ui::style_mut`] to change the style of a single [`Ui`].
     pub fn set_style(&self, style: impl Into<Arc<Style>>) {
-        self.options_mut(|opt| opt.style = style.into());
+        self.options_mut(|opt| opt.style.set_active(style.into()));
     }
 
     /// The [`Visuals`] used by all subsequent windows, panels etc.
@@ -1609,7 +1628,7 @@ impl Context {
     /// ctx.set_visuals(egui::Visuals::light()); // Switch to light mode
     /// ```
     pub fn set_visuals(&self, visuals: crate::Visuals) {
-        self.options_mut(|opt| std::sync::Arc::make_mut(&mut opt.style).visuals = visuals);
+        self.options_mut(|opt| opt.style.active_mut().visuals = visuals);
     }
 
     /// The number of physical pixels for each logical point.
@@ -2431,7 +2450,7 @@ impl Context {
     /// Whether or not to debug widget layout on hover.
     #[cfg(debug_assertions)]
     pub fn debug_on_hover(&self) -> bool {
-        self.options(|opt| opt.style.debug.debug_on_hover)
+        self.options(|opt| opt.style.active().debug.debug_on_hover)
     }
 
     /// Turn on/off whether or not to debug widget layout on hover.

crates/egui/src/memory.rs

@@ -4,8 +4,8 @@ use ahash::{HashMap, HashSet};
 use epaint::emath::TSTransform;
 
 use crate::{
-    area, vec2, EventFilter, Id, IdMap, LayerId, Order, Pos2, Rangef, RawInput, Rect, Style, Vec2,
-    ViewportId, ViewportIdMap, ViewportIdSet,
+    area, vec2, EventFilter, Id, IdMap, LayerId, Order, Pos2, Rangef, RawInput, Rect, Style, Theme,
+    Vec2, ViewportId, ViewportIdMap, ViewportIdSet,
 };
 
 // ----------------------------------------------------------------------------
@@ -166,8 +166,7 @@ impl FocusDirection {
 #[cfg_attr(feature = "serde", serde(default))]
 pub struct Options {
     /// The default style for new [`Ui`](crate::Ui):s.
-    #[cfg_attr(feature = "serde", serde(skip))]
-    pub(crate) style: std::sync::Arc<Style>,
+    pub(crate) style: StyleSet,
 
     /// Global zoom factor of the UI.
     ///
@@ -250,6 +249,72 @@ pub struct Options {
     pub reduce_texture_memory: bool,
 }
 
+#[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "serde", serde(default))]
+pub struct StyleSet {
+    /// The default style for new [`Ui`](crate::Ui):s in dark mode.
+    #[cfg_attr(feature = "serde", serde(skip))]
+    pub(crate) dark: std::sync::Arc<Style>,
+
+    /// The default style for new [`Ui`](crate::Ui):s in light mode.
+    #[cfg_attr(feature = "serde", serde(skip))]
+    pub(crate) light: std::sync::Arc<Style>,
+
+    /// Dark or light style? Default is [`Theme::Dark`].
+    pub theme: Theme,
+
+    /// Change [`Self::theme`] based on [`RawInput::system_theme`]?
+    pub follow_system_theme: bool,
+}
+
+impl Default for StyleSet {
+    fn default() -> Self {
+        Self {
+            dark: Default::default(),
+            light: std::sync::Arc::new(Style::light()),
+            theme: Default::default(),
+            follow_system_theme: true,
+        }
+    }
+}
+
+impl StyleSet {
+    pub(crate) fn update(&mut self, system_theme: Option<Theme>) {
+        log::info!(
+            "updating style set with theme: {system_theme:?}, follow={}",
+            self.follow_system_theme
+        );
+        if self.follow_system_theme {
+            if let Some(system_theme) = system_theme {
+                self.theme = system_theme;
+            }
+        }
+    }
+
+    pub(crate) fn active(&self) -> &std::sync::Arc<Style> {
+        match self.theme {
+            Theme::Dark => &self.dark,
+            Theme::Light => &self.light,
+        }
+    }
+
+    pub(crate) fn active_mut(&mut self) -> &mut Style {
+        use std::sync::Arc;
+        match self.theme {
+            Theme::Dark => Arc::make_mut(&mut self.dark),
+            Theme::Light => Arc::make_mut(&mut self.light),
+        }
+    }
+
+    pub(crate) fn set_active(&mut self, style: std::sync::Arc<Style>) {
+        match self.theme {
+            Theme::Dark => self.dark = style,
+            Theme::Light => self.light = style,
+        }
+    }
+}
+
 impl Default for Options {
     fn default() -> Self {
         // TODO(emilk): figure out why these constants need to be different on web and on native (winit).
@@ -320,7 +385,7 @@ impl Options {
         CollapsingHeader::new("🎑 Style")
             .default_open(true)
             .show(ui, |ui| {
-                std::sync::Arc::make_mut(style).ui(ui);
+                style.active_mut().ui(ui);
             });
 
         CollapsingHeader::new("✒ Painting")

crates/egui/src/style.rs

@@ -289,6 +289,13 @@ fn style_impl_send_sync() {
 }
 
 impl Style {
+    pub(crate) fn light() -> Self {
+        Self {
+            visuals: Visuals::light(),
+            ..Default::default()
+        }
+    }
+
     // TODO(emilk): rename style.interact() to maybe… `style.interactive` ?
     /// Use this style for interactive things.
     /// Note that you must already have a response,
@@ -930,10 +937,11 @@ impl Visuals {
 }
 
 /// Dark or Light theme.
-#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)]
 #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub enum Theme {
     /// Dark mode: light text on a dark background.
+    #[default]
     Dark,
 
     /// Light mode: dark text on a light background.