Draft: new eugi StyleEngine and example custom styling system

crates/egui/src/containers/collapsing_header.rs

@@ -1,5 +1,7 @@
 use std::hash::Hash;
 
+use crate::style::WidgetVisuals;
+use crate::style_trait::{Classes, WidgetName};
 use crate::{
     Context, Id, InnerResponse, NumExt as _, Rect, Response, Sense, Stroke, TextStyle,
     TextWrapMode, Ui, UiBuilder, UiKind, UiStackInfo, Vec2, WidgetInfo, WidgetText, WidgetType,
@@ -580,7 +582,11 @@ impl CollapsingHeader {
         let openness = state.openness(ui.ctx());
 
         if ui.is_rect_visible(rect) {
-            let visuals = ui.style().interact_selectable(&header_response, selected);
+            let visuals: WidgetVisuals = ui.widget_style(
+                WidgetName::Custom("CollapsingHeader".into()),
+                &header_response,
+                &Classes::default().with_if("selected", selected),
+            );
 
             if ui.visuals().collapsing_header_frame || show_background {
                 ui.painter().add(epaint::RectShape::new(

crates/egui/src/lib.rs

@@ -446,6 +446,7 @@ mod atomics;
 #[cfg(feature = "callstack")]
 #[cfg(debug_assertions)]
 mod callstack;
+pub mod style_trait;
 
 #[cfg(feature = "accesskit")]
 pub use accesskit;

crates/egui/src/style_trait.rs

@@ -0,0 +1,175 @@
+use crate::style::WidgetVisuals;
+use crate::{Context, Frame, Id, Response, TextStyle, Ui};
+use emath::TSTransform;
+use epaint::text::TextFormat;
+use epaint::{CornerRadius, Stroke};
+use std::borrow::Cow;
+use std::fmt::Debug;
+use std::sync::Arc;
+
+#[derive(Debug, Clone)]
+pub enum WidgetName {
+    Button,
+    Checkbox,
+    Slider,
+    TextInput,
+    Custom(Cow<'static, str>),
+}
+
+#[derive(Clone)]
+pub struct WidgetContext<'c> {
+    pub ui: &'c Ui,
+    pub response: &'c Response,
+    pub classes: &'c Classes,
+    pub name: WidgetName,
+}
+
+impl Debug for WidgetContext<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("WidgetContext")
+            .field("name", &self.name)
+            .field("classes", &self.classes.classes)
+            .finish()
+    }
+}
+
+const CLASS_SELECTED: &str = "selected";
+
+pub trait StyleEngine<T>: Send + Sync {
+    fn get(&self, ctx: &WidgetContext) -> T;
+}
+
+#[derive(Clone)]
+pub struct DefaultWidgetStyle;
+
+impl StyleEngine<WidgetVisuals> for DefaultWidgetStyle {
+    fn get(&self, ctx: &WidgetContext) -> WidgetVisuals {
+        ctx.ui
+            .style()
+            .interact_selectable(ctx.response, ctx.classes.has(CLASS_SELECTED))
+    }
+}
+
+fn widget_style_id() -> Id {
+    Id::new("WidgetStyle")
+}
+
+impl Ui {
+    pub fn widget_style<T: 'static>(
+        &self,
+        name: WidgetName,
+        response: &Response,
+        classes: &Classes,
+    ) -> T {
+        let style = self.data_mut(|d| {
+            let style: StyleEngineContainer<T> =
+                d.get_temp(widget_style_id()).expect("Widget style not set");
+            style
+        });
+        let ctx = WidgetContext {
+            ui: self,
+            response: &response,
+            classes,
+            name,
+        };
+
+        style.0.get(&ctx)
+    }
+}
+
+impl Context {
+    pub fn set_style_engine<T: 'static>(&self, style: impl StyleEngine<T> + 'static) {
+        self.data_mut(|d| {
+            d.insert_temp(widget_style_id(), StyleEngineContainer(Arc::new(style)));
+        });
+    }
+}
+
+struct StyleEngineContainer<T>(Arc<dyn StyleEngine<T>>);
+
+impl<T> Clone for StyleEngineContainer<T> {
+    fn clone(&self) -> Self {
+        StyleEngineContainer(self.0.clone())
+    }
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct Classes {
+    pub classes: smallvec::SmallVec<[&'static str; 1]>,
+}
+
+impl Classes {
+    pub fn with_if(mut self, class: &'static str, condition: bool) -> Self {
+        if condition {
+            self.classes.push(class);
+        }
+        self
+    }
+
+    pub fn add_if(&mut self, class: &'static str, condition: bool) {
+        if condition {
+            self.classes.push(class);
+        }
+    }
+
+    pub fn has(&self, class: &str) -> bool {
+        self.classes.contains(&class)
+    }
+}
+
+pub trait HasClasses {
+    fn classes(&self) -> &Classes;
+
+    fn classes_mut(&mut self) -> &mut Classes;
+
+    fn add_class(&mut self, class: &'static str) -> &Self {
+        self.classes_mut().add_if(class, true);
+        self
+    }
+
+    fn with_class(mut self, class: &'static str) -> Self
+    where
+        Self: Sized,
+    {
+        self.classes_mut().add_if(class, true);
+        self
+    }
+
+    fn with_class_if(mut self, class: &'static str, condition: bool) -> Self
+    where
+        Self: Sized,
+    {
+        self.classes_mut().add_if(class, condition);
+        self
+    }
+}
+
+#[derive(Debug, Clone, Default)]
+pub struct WidgetStyle {
+    /// Background color, stroke, margin, and shadow.
+    pub frame: Frame,
+
+    /// What font to use and at what size.
+    pub text: TextFormat,
+
+    /// Color and width of e.g. checkbox checkmark.
+    /// Also text color.
+    ///
+    /// Note that this is different from the frame border color.
+    pub stroke: Stroke,
+
+    pub transform: TSTransform,
+}
+
+impl From<WidgetStyle> for WidgetVisuals {
+    fn from(value: WidgetStyle) -> Self {
+        Self {
+            bg_stroke: value.frame.stroke,
+            bg_fill: value.frame.fill,
+            fg_stroke: value.stroke,
+            corner_radius: value.frame.corner_radius,
+            weak_bg_fill: value.frame.fill,
+            expansion: value.frame.inner_margin.sum().length(),
+        }
+    }
+}

crates/egui/src/util/id_type_map.rs

@@ -192,6 +192,13 @@ impl Element {
         }
     }
 
+    pub(crate) fn into_temp<T: 'static>(self) -> Option<T> {
+        match self {
+            Self::Value { value, .. } => value.downcast().ok().map(|b| *b),
+            Self::Serialized(_) => None,
+        }
+    }
+
     #[inline]
     pub(crate) fn get_temp_mut_or_insert_with<T: 'static + Any + Clone + Send + Sync>(
         &mut self,
@@ -485,10 +492,10 @@ impl IdTypeMap {
 
     /// Remove and fetch the state of this type and id.
     #[inline]
-    pub fn remove_temp<T: 'static + Default>(&mut self, id: Id) -> Option<T> {
+    pub fn remove_temp<T: 'static>(&mut self, id: Id) -> Option<T> {
         let hash = hash(TypeId::of::<T>(), id);
         let mut element = self.map.remove(&hash)?;
-        Some(std::mem::take(element.get_mut_temp()?))
+        element.into_temp()
     }
 
     /// Note all state of the given type.

crates/egui/src/widgets/button.rs

@@ -1,8 +1,12 @@
+use crate::style::WidgetVisuals;
+use crate::style_trait::{Classes, HasClasses, WidgetName, WidgetStyle};
 use crate::{
     Atom, AtomExt as _, AtomKind, AtomLayout, AtomLayoutResponse, Color32, CornerRadius, Frame,
-    Image, IntoAtoms, NumExt as _, Response, Sense, Stroke, TextWrapMode, Ui, Vec2, Widget,
-    WidgetInfo, WidgetText, WidgetType,
+    Image, IntoAtoms, NumExt as _, Response, RichText, Sense, SizedAtomKind, Stroke, TextWrapMode,
+    Ui, Vec2, Widget, WidgetInfo, WidgetText, WidgetType,
 };
+use std::mem;
+use std::sync::Arc;
 
 /// Clickable button with text.
 ///
@@ -35,6 +39,17 @@ pub struct Button<'a> {
     selected: bool,
     image_tint_follows_text_color: bool,
     limit_image_size: bool,
+    classes: Classes,
+}
+
+impl HasClasses for Button<'_> {
+    fn classes(&self) -> &Classes {
+        &self.classes
+    }
+
+    fn classes_mut(&mut self) -> &mut Classes {
+        &mut self.classes
+    }
 }
 
 impl<'a> Button<'a> {
@@ -51,6 +66,7 @@ impl<'a> Button<'a> {
             selected: false,
             image_tint_follows_text_color: false,
             limit_image_size: false,
+            classes: Classes::default(),
         }
     }
 
@@ -261,6 +277,7 @@ impl<'a> Button<'a> {
             selected,
             image_tint_follows_text_color,
             limit_image_size,
+            classes,
         } = self;
 
         if !small {
@@ -290,44 +307,57 @@ impl<'a> Button<'a> {
             button_padding.y = 0.0;
         }
 
-        let mut prepared = layout
-            .frame(Frame::new().inner_margin(button_padding))
-            .min_size(min_size)
-            .allocate(ui);
+        let response = ui.ctx().read_response(ui.next_auto_id());
+
+        let style: WidgetStyle = response
+            .map(|r| ui.widget_style(WidgetName::Button, &r, &classes))
+            .unwrap_or_default();
+
+        layout.map_texts(|t| match t {
+            WidgetText::RichText(mut text) => {
+                let mut text_mut = Arc::make_mut(&mut text);
+                *text_mut = mem::take(text_mut).font(style.text.font_id.clone());
+                WidgetText::RichText(text)
+            }
+            WidgetText::Text(text) => {
+                let mut rich_text = RichText::new(text.clone()).font(style.text.font_id.clone());
+                WidgetText::RichText(Arc::new(rich_text))
+            }
+            w => w,
+        });
+
+        let mut prepared = layout.frame(style.frame).min_size(min_size).allocate(ui);
 
         let response = if ui.is_rect_visible(prepared.response.rect) {
-            let visuals = ui.style().interact_selectable(&prepared.response, selected);
+            // let visuals = ui.style().interact_selectable(&prepared.response, selected);
+            let visuals: WidgetStyle = ui.widget_style(
+                WidgetName::Button,
+                &prepared.response,
+                &classes.with_if("selected", selected),
+            );
+            ui.with_visual_transform(visuals.transform, |ui| {
+                let visible_frame = if frame_when_inactive {
+                    has_frame_margin
+                } else {
+                    has_frame_margin
+                        && (prepared.response.hovered()
+                            || prepared.response.is_pointer_button_down_on()
+                            || prepared.response.has_focus())
+                };
 
-            let visible_frame = if frame_when_inactive {
-                has_frame_margin
-            } else {
-                has_frame_margin
-                    && (prepared.response.hovered()
-                        || prepared.response.is_pointer_button_down_on()
-                        || prepared.response.has_focus())
-            };
+                if image_tint_follows_text_color {
+                    prepared.map_images(|image| image.tint(visuals.text.color));
+                }
 
-            if image_tint_follows_text_color {
-                prepared.map_images(|image| image.tint(visuals.text_color()));
-            }
+                prepared.fallback_text_color = visuals.text.color;
 
-            prepared.fallback_text_color = visuals.text_color();
+                if visible_frame {
+                    prepared.frame = visuals.frame;
+                };
 
-            if visible_frame {
-                let stroke = stroke.unwrap_or(visuals.bg_stroke);
-                let fill = fill.unwrap_or(visuals.weak_bg_fill);
-                prepared.frame = prepared
-                    .frame
-                    .inner_margin(
-                        button_padding + Vec2::splat(visuals.expansion) - Vec2::splat(stroke.width),
-                    )
-                    .outer_margin(-Vec2::splat(visuals.expansion))
-                    .fill(fill)
-                    .stroke(stroke)
-                    .corner_radius(corner_radius.unwrap_or(visuals.corner_radius));
-            };
-
-            prepared.paint(ui)
+                prepared.paint(ui)
+            })
+            .inner
         } else {
             AtomLayoutResponse::empty(prepared.response)
         };

examples/hello_world_simple/src/main.rs

@@ -2,6 +2,15 @@
 #![allow(rustdoc::missing_crate_level_docs)] // it's an example
 
 use eframe::egui;
+use eframe::egui::style::WidgetVisuals;
+use eframe::egui::style_trait::{
+    Classes, DefaultWidgetStyle, HasClasses, StyleEngine, WidgetContext, WidgetName, WidgetStyle,
+};
+use eframe::egui::{
+    Button, Color32, FontFamily, FontId, Frame, Margin, Response, Stroke, TextFormat,
+};
+use eframe::emath::TSTransform;
+use std::fmt::Display;
 
 fn main() -> eframe::Result {
     env_logger::init(); // Log to stderr (if you run with `RUST_LOG=debug`).
@@ -16,6 +25,10 @@ fn main() -> eframe::Result {
     let mut age = 42;
 
     eframe::run_simple_native("My egui App", options, move |ctx, _frame| {
+        ctx.set_style_engine(MyCustomWidgetStyle {
+            default: DefaultWidgetStyle,
+        });
+
         egui::CentralPanel::default().show(ctx, |ui| {
             ui.heading("My egui Application");
             ui.horizontal(|ui| {
@@ -28,6 +41,227 @@ fn main() -> eframe::Result {
                 age += 1;
             }
             ui.label(format!("Hello '{name}', age {age}"));
+
+            ui.horizontal(|ui| {
+                ui.add(Button::new("Primary Button").primary());
+                ui.add(Button::new("Secondary Button").secondary());
+                ui.add(Button::new("Normal Button"));
+            });
+
+            ui.horizontal(|ui| {
+                ui.add(Button::new("Large Primary").primary().lg());
+                ui.add(Button::new("Large Secondary").secondary().lg());
+                ui.add(Button::new("Small Normal").sm());
+            });
         });
     })
 }
+
+#[derive(Clone)]
+struct MyCustomWidgetStyle {
+    // Can fallback to DefaultWidgetStyle
+    default: DefaultWidgetStyle,
+}
+
+enum Variant {
+    Primary,
+    Secondary,
+    Normal,
+}
+
+impl Display for Variant {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Variant::Primary => write!(f, "primary"),
+            Variant::Secondary => write!(f, "secondary"),
+            Variant::Normal => write!(f, "normal"),
+        }
+    }
+}
+
+impl Variant {
+    fn from_classes(classes: &Classes) -> Self {
+        if classes.has("primary") {
+            Variant::Primary
+        } else if classes.has("secondary") {
+            Variant::Secondary
+        } else {
+            Variant::Normal
+        }
+    }
+
+    fn color(&self) -> Color32 {
+        match self {
+            Variant::Primary => Color32::LIGHT_RED,
+            Variant::Secondary => Color32::LIGHT_BLUE,
+            Variant::Normal => Color32::LIGHT_GRAY,
+        }
+    }
+
+    fn contrast_color(&self) -> Color32 {
+        match self {
+            Variant::Primary => Color32::WHITE,
+            Variant::Secondary => Color32::BLACK,
+            Variant::Normal => Color32::BLACK,
+        }
+    }
+}
+
+enum Size {
+    Sm,
+    Md,
+    Lg,
+}
+
+impl Display for Size {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Size::Sm => write!(f, "sm"),
+            Size::Md => write!(f, "md"),
+            Size::Lg => write!(f, "lg"),
+        }
+    }
+}
+
+impl Size {
+    fn from_classes(classes: &Classes) -> Self {
+        if classes.has("sm") {
+            Size::Sm
+        } else if classes.has("md") {
+            Size::Md
+        } else if classes.has("lg") {
+            Size::Lg
+        } else {
+            Size::Md // Default size
+        }
+    }
+
+    fn inner_margin(&self) -> Margin {
+        match self {
+            Size::Sm => Margin::symmetric(2, 2),
+            Size::Md => Margin::symmetric(4, 4),
+            Size::Lg => Margin::symmetric(6, 6),
+        }
+    }
+
+    fn font_size(&self) -> f32 {
+        match self {
+            Size::Sm => 12.0,
+            Size::Md => 14.0,
+            Size::Lg => 16.0,
+        }
+    }
+
+    fn frame_rounding(&self) -> f32 {
+        match self {
+            Size::Sm => 2.0,
+            Size::Md => 4.0,
+            Size::Lg => 6.0,
+        }
+    }
+}
+
+impl StyleEngine<WidgetStyle> for MyCustomWidgetStyle {
+    fn get(&self, ctx: &WidgetContext) -> WidgetStyle {
+        // let mut visuals = self.default.get(ctx);
+
+        let variant = Variant::from_classes(&ctx.classes);
+
+        let size = Size::from_classes(&ctx.classes);
+
+        let mut style = WidgetStyle {
+            frame: Frame::new()
+                .fill(variant.color())
+                .inner_margin(size.inner_margin())
+                .corner_radius(size.frame_rounding()),
+            text: TextFormat::simple(
+                FontId::new(size.font_size(), FontFamily::Proportional),
+                variant.contrast_color(),
+            ),
+            stroke: Stroke::default(),
+            transform: TSTransform::default(),
+        };
+
+        let state = if ctx.response.is_pointer_button_down_on() {
+            -1.0
+        } else if ctx.response.hovered() {
+            1.0
+        } else {
+            0.0
+        };
+
+        let state_animated =
+            ctx.ui
+                .ctx()
+                .animate_value_with_time(ctx.response.id.with("style_anim"), state, 0.05);
+
+        let lerp_to_darken = Color32::BLACK;
+        let lerp_to_lighten = Color32::WHITE;
+
+        if state_animated < 0.0 {
+            style.frame.fill = variant
+                .color()
+                .lerp_to_gamma(lerp_to_darken, 0.03 * -state_animated);
+        } else if state_animated > 0.0 {
+            style.frame.fill = variant
+                .color()
+                .lerp_to_gamma(lerp_to_lighten, 0.1 * state_animated);
+        }
+
+        match ctx.name {
+            WidgetName::Button => {
+                let scale = 1.0 + state_animated * 0.02;
+                if scale != 1.0 {
+                    // style.frame.inner_margin += 4;
+                    let center = ctx.response.rect.center().to_vec2();
+                    style.transform = TSTransform::from_translation(center)
+                        * TSTransform::from_scaling(scale)
+                        * TSTransform::from_translation(-center);
+                }
+            }
+            WidgetName::Checkbox => {}
+            WidgetName::Slider => {}
+            WidgetName::TextInput => {}
+            WidgetName::Custom(_) => {}
+        }
+
+        style
+    }
+}
+
+// trait ClassExt {
+//     fn primary(self) -> Self;
+// }
+//
+// impl<T> ClassExt for T where T: HasClasses {
+//     fn primary(self) -> Self {
+//         self.with_class("primary")
+//     }
+// }
+
+macro_rules! classes {
+    ($trait_name:ident: ($($name:ident, )+)) => {
+        // pub enum $trait_name {
+        //     $(
+        //         $name,
+        //     )*
+        // }
+
+        pub trait $trait_name {
+            $(
+                fn $name(self) -> Self;
+            )*
+        }
+
+        impl<T> $trait_name for T
+        where
+            T: HasClasses,
+        {
+                $(fn $name(mut self) -> Self {
+                    self.with_class(stringify!($name))
+                })?
+        }
+    };
+}
+
+classes!(CustomStyle: (primary, secondary, normal, sm, md, lg, ));