add sizable trait

crates/theme/src/lib.rs

@@ -47,6 +47,9 @@ pub struct Theme {
     pub colors: ColorTokens,
     pub ramps: Ramps,
     pub radius: Radius,
+    /// The platform's native root font size; rem-based sizing scales with it.
+    pub root_font_size: Pixels,
+    pub sizes: SizeTable,
     pub accessibility: AccessibilityPreferences,
 }
 
@@ -72,6 +75,78 @@ impl Default for Radius {
     }
 }
 
+/// A named control size class.
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub enum Size {
+    Small,
+    /// The default.
+    #[default]
+    Medium,
+    Large,
+}
+
+/// The control metrics for one size class.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct ControlMetrics {
+    /// Push buttons, toggles, and field rows.
+    pub control_height: Pixels,
+    /// Text fields; slightly taller than buttons, as native fields are.
+    pub input_height: Pixels,
+    /// Horizontal padding inside controls.
+    pub padding_x: Pixels,
+    /// Label text size.
+    pub text_size: Pixels,
+    /// Icons and on/off indicators.
+    pub icon_size: Pixels,
+    /// Avatars.
+    pub avatar_size: Pixels,
+}
+
+/// The control metrics for every size class, derived from the theme's root
+/// font size so controls scale with the platform's native type.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct SizeTable {
+    pub small: ControlMetrics,
+    pub medium: ControlMetrics,
+    pub large: ControlMetrics,
+}
+
+impl SizeTable {
+    pub fn with_root_font_size(rem_size: Pixels) -> Self {
+        let class = |height: f32, padding: f32, text: f32, icon: f32, avatar: f32| ControlMetrics {
+            control_height: rem_size * height,
+            input_height: rem_size * (height + 0.125),
+            padding_x: rem_size * padding,
+            text_size: rem_size * text,
+            icon_size: rem_size * icon,
+            avatar_size: rem_size * avatar,
+        };
+        Self {
+            small: class(1.5, 0.75, 0.85, 0.875, 1.5),
+            medium: class(1.75, 1.0, 1.0, 1.0, 2.0),
+            large: class(2.25, 1.25, 1.15, 1.25, 3.0),
+        }
+    }
+
+    /// The metrics for `size`.
+    pub fn resolve(&self, size: Size) -> ControlMetrics {
+        match size {
+            Size::Small => self.small,
+            Size::Medium => self.medium,
+            Size::Large => self.large,
+        }
+    }
+
+    /// Sets the medium class's text-field height to the platform's stated
+    /// value, scaling the other classes by the same ratio.
+    pub fn set_input_height(&mut self, medium_input_height: Pixels) {
+        let ratio = medium_input_height / self.medium.input_height;
+        self.small.input_height *= ratio;
+        self.medium.input_height = medium_input_height;
+        self.large.input_height *= ratio;
+    }
+}
+
 /// Reads the resolved theme global from any app context.
 pub trait ActiveTheme {
     fn theme(&self) -> &Theme;
@@ -95,6 +170,8 @@ impl Theme {
             colors: resolved.colors,
             ramps: resolved.ramps,
             radius: resolved.radius,
+            root_font_size: resolved.root_font_size,
+            sizes: resolved.sizes,
             accessibility: resolved.accessibility,
         }
     }
@@ -114,7 +191,7 @@ impl Theme {
     /// Re-resolves when a window's appearance differs from the resolved variant.
     ///
     /// Wire to `Window::observe_window_appearance`.
-    pub fn sync_from_window(window: &gpui::Window, cx: &mut App) {
+    pub fn sync_from_window(window: &mut gpui::Window, cx: &mut App) {
         let variant = ThemeVariant::from_appearance(window.appearance());
         if cx.global::<Theme>().variant != variant
             || cx.global::<ThemeEngine>().mode_override.is_none()
@@ -122,6 +199,11 @@ impl Theme {
             reapply(cx);
         }
     }
+
+    /// Sizes the window's rem to the theme's root font size.
+    pub fn sync_window_rem_size(window: &mut gpui::Window, cx: &App) {
+        window.set_rem_size(cx.global::<Theme>().root_font_size);
+    }
 }
 
 /// The engine's knobs and its platform source.