gpui: Implement dynamic window control elements (#30828)

Allows setting element as window control elements which consist of
`Drag`, `Close`, `Max`, or `Min`. This allows you to implement
dynamically sized elements that control the platform window, this is
used for areas such as the title bar. Currently only implemented for
Windows.

Release Notes:

- N/A

crates/title_bar/src/platforms/platform_windows.rs

@@ -1,4 +1,4 @@
-use gpui::{Rgba, WindowAppearance, prelude::*};
+use gpui::{Rgba, WindowAppearance, WindowControlArea, prelude::*};
 
 use ui::prelude::*;
 
@@ -118,17 +118,12 @@ impl WindowsCaptionButton {
 
 impl RenderOnce for WindowsCaptionButton {
     fn render(self, _window: &mut Window, _cx: &mut App) -> impl IntoElement {
-        // todo(windows) report this width to the Windows platform API
-        // NOTE: this is intentionally hard coded. An option to use the 'native' size
-        //       could be added when the width is reported to the Windows platform API
-        //       as this could change between future Windows versions.
-        let width = px(36.);
-
         h_flex()
             .id(self.id)
             .justify_center()
             .content_center()
-            .w(width)
+            .occlude()
+            .w(px(36.))
             .h_full()
             .text_size(px(10.0))
             .hover(|style| style.bg(self.hover_background_color))
@@ -138,6 +133,17 @@ impl RenderOnce for WindowsCaptionButton {
 
                 style.bg(active_color)
             })
+            .map(|this| match self.icon {
+                WindowsCaptionButtonIcon::Close => {
+                    this.window_control_area(WindowControlArea::Close)
+                }
+                WindowsCaptionButtonIcon::Maximize | WindowsCaptionButtonIcon::Restore => {
+                    this.window_control_area(WindowControlArea::Max)
+                }
+                WindowsCaptionButtonIcon::Minimize => {
+                    this.window_control_area(WindowControlArea::Min)
+                }
+            })
             .child(match self.icon {
                 WindowsCaptionButtonIcon::Minimize => "\u{e921}",
                 WindowsCaptionButtonIcon::Restore => "\u{e923}",

crates/title_bar/src/title_bar.rs

@@ -22,7 +22,8 @@ use client::{Client, UserStore};
 use gpui::{
     Action, AnyElement, App, Context, Corner, Decorations, Element, Entity, InteractiveElement,
     Interactivity, IntoElement, MouseButton, ParentElement, Render, Stateful,
-    StatefulInteractiveElement, Styled, Subscription, WeakEntity, Window, actions, div, px,
+    StatefulInteractiveElement, Styled, Subscription, WeakEntity, Window, WindowControlArea,
+    actions, div, px,
 };
 use onboarding_banner::OnboardingBanner;
 use project::Project;
@@ -143,6 +144,7 @@ impl Render for TitleBar {
 
         h_flex()
             .id("titlebar")
+            .window_control_area(WindowControlArea::Drag)
             .w_full()
             .h(height)
             .map(|this| {