gpui: Add support for window transparency & blur on macOS (#9610)

This PR adds support for transparent and blurred window backgrounds on
macOS.

Release Notes:

- Added support for transparent and blurred window backgrounds on macOS
([#5040](https://github.com/zed-industries/zed/issues/5040)).
- This requires themes to specify a new `background.appearance` key
("opaque", "transparent" or "blurred") and to include an alpha value in
colors that should be transparent.

<img width="913" alt="image"
src="https://github.com/zed-industries/zed/assets/2588851/7547ee2a-e376-4d55-9114-e6fc2f5110bc">
<img width="994" alt="image"
src="https://github.com/zed-industries/zed/assets/2588851/b36fbc14-6e4d-4140-9448-69cad803c45a">
<img width="1020" alt="image"
src="https://github.com/zed-industries/zed/assets/2588851/d70e2005-54fd-4991-a211-ed484ccf26ef">

---------

Co-authored-by: Luiz Marcondes <luizgustavodevergennes@gmail.com>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/theme/src/default_theme.rs

@@ -1,5 +1,7 @@
 use std::sync::Arc;
 
+use gpui::WindowBackgroundAppearance;
+
 use crate::prelude::*;
 
 use crate::{
@@ -15,6 +17,7 @@ fn zed_pro_daylight() -> Theme {
         name: "Zed Pro Daylight".into(),
         appearance: Appearance::Light,
         styles: ThemeStyles {
+            window_background_appearance: WindowBackgroundAppearance::Opaque,
             system: SystemColors::default(),
             colors: ThemeColors::light(),
             status: StatusColors::light(),
@@ -45,6 +48,7 @@ pub(crate) fn zed_pro_moonlight() -> Theme {
         name: "Zed Pro Moonlight".into(),
         appearance: Appearance::Dark,
         styles: ThemeStyles {
+            window_background_appearance: WindowBackgroundAppearance::Opaque,
             system: SystemColors::default(),
             colors: ThemeColors::dark(),
             status: StatusColors::dark(),

crates/theme/src/one_themes.rs

@@ -1,6 +1,6 @@
 use std::sync::Arc;
 
-use gpui::{hsla, FontStyle, FontWeight, HighlightStyle};
+use gpui::{hsla, FontStyle, FontWeight, HighlightStyle, WindowBackgroundAppearance};
 
 use crate::{
     default_color_scales, Appearance, PlayerColors, StatusColors, SyntaxTheme, SystemColors, Theme,
@@ -39,8 +39,8 @@ pub(crate) fn one_dark() -> Theme {
         id: "one_dark".to_string(),
         name: "One Dark".into(),
         appearance: Appearance::Dark,
-
         styles: ThemeStyles {
+            window_background_appearance: WindowBackgroundAppearance::Opaque,
             system: SystemColors::default(),
             colors: ThemeColors {
                 border: hsla(225. / 360., 13. / 100., 12. / 100., 1.),

crates/theme/src/registry.rs

@@ -122,6 +122,13 @@ impl ThemeRegistry {
                 AppearanceContent::Light => SyntaxTheme::light(),
                 AppearanceContent::Dark => SyntaxTheme::dark(),
             };
+
+            let window_background_appearance = user_theme
+                .style
+                .window_background_appearance
+                .map(Into::into)
+                .unwrap_or_default();
+
             if !user_theme.style.syntax.is_empty() {
                 syntax_colors.highlights = user_theme
                     .style
@@ -153,6 +160,7 @@ impl ThemeRegistry {
                 },
                 styles: ThemeStyles {
                     system: SystemColors::default(),
+                    window_background_appearance,
                     colors: theme_colors,
                     status: status_colors,
                     player: player_colors,

crates/theme/src/schema.rs

@@ -1,5 +1,5 @@
 use anyhow::Result;
-use gpui::{FontStyle, FontWeight, HighlightStyle, Hsla};
+use gpui::{FontStyle, FontWeight, HighlightStyle, Hsla, WindowBackgroundAppearance};
 use indexmap::IndexMap;
 use palette::FromColor;
 use schemars::gen::SchemaGenerator;
@@ -33,6 +33,25 @@ pub enum AppearanceContent {
     Dark,
 }
 
+/// The background appearance of the window.
+#[derive(Debug, PartialEq, Clone, Copy, Serialize, Deserialize, JsonSchema)]
+#[serde(rename_all = "snake_case")]
+pub enum WindowBackgroundContent {
+    Opaque,
+    Transparent,
+    Blurred,
+}
+
+impl From<WindowBackgroundContent> for WindowBackgroundAppearance {
+    fn from(value: WindowBackgroundContent) -> Self {
+        match value {
+            WindowBackgroundContent::Opaque => WindowBackgroundAppearance::Opaque,
+            WindowBackgroundContent::Transparent => WindowBackgroundAppearance::Transparent,
+            WindowBackgroundContent::Blurred => WindowBackgroundAppearance::Blurred,
+        }
+    }
+}
+
 /// The content of a serialized theme family.
 #[derive(Debug, Clone, Serialize, Deserialize, JsonSchema)]
 pub struct ThemeFamilyContent {
@@ -53,6 +72,9 @@ pub struct ThemeContent {
 #[derive(Debug, Clone, Default, Serialize, Deserialize, JsonSchema)]
 #[serde(default)]
 pub struct ThemeStyleContent {
+    #[serde(default, rename = "background.appearance")]
+    pub window_background_appearance: Option<WindowBackgroundContent>,
+
     #[serde(flatten, default)]
     pub colors: ThemeColorsContent,
 

crates/theme/src/settings.rs

@@ -244,6 +244,12 @@ impl ThemeSettings {
         if let Some(theme_overrides) = &self.theme_overrides {
             let mut base_theme = (*self.active_theme).clone();
 
+            if let Some(window_background_appearance) = theme_overrides.window_background_appearance
+            {
+                base_theme.styles.window_background_appearance =
+                    window_background_appearance.into();
+            }
+
             base_theme
                 .styles
                 .colors

crates/theme/src/styles/colors.rs

@@ -1,4 +1,4 @@
-use gpui::Hsla;
+use gpui::{Hsla, WindowBackgroundAppearance};
 use refineable::Refineable;
 use std::sync::Arc;
 
@@ -235,6 +235,8 @@ pub struct ThemeColors {
 
 #[derive(Refineable, Clone)]
 pub struct ThemeStyles {
+    /// The background appearance of the window.
+    pub window_background_appearance: WindowBackgroundAppearance,
     pub system: SystemColors,
     /// An array of colors used for theme elements that iterate through a series of colors.
     ///

crates/theme/src/theme.rs

@@ -27,7 +27,9 @@ pub use schema::*;
 pub use settings::*;
 pub use styles::*;
 
-use gpui::{AppContext, AssetSource, Hsla, SharedString, WindowAppearance};
+use gpui::{
+    AppContext, AssetSource, Hsla, SharedString, WindowAppearance, WindowBackgroundAppearance,
+};
 use serde::Deserialize;
 
 #[derive(Debug, PartialEq, Clone, Copy, Deserialize)]
@@ -158,6 +160,12 @@ impl Theme {
     pub fn appearance(&self) -> Appearance {
         self.appearance
     }
+
+    /// Returns the [`WindowBackgroundAppearance`] for the theme.
+    #[inline(always)]
+    pub fn window_background_appearance(&self) -> WindowBackgroundAppearance {
+        self.styles.window_background_appearance
+    }
 }
 
 pub fn color_alpha(color: Hsla, alpha: f32) -> Hsla {