On macOS, add support for Window::set_blur

CHANGELOG.md

@@ -17,6 +17,7 @@ Unreleased` header.
 - On Wayland, use `configure_bounds` to constrain `with_inner_size` when compositor wants users to pick size.
 - On Windows, fix deadlock when accessing the state during `Cursor{Enter,Leave}`.
 - On macOS, fix deadlock when entering a nested event loop from an event handler.
+- On macOS, add support for `Window::set_blur`.
 
 # 0.29.2
 

src/platform_impl/macos/appkit/window.rs

@@ -36,6 +36,9 @@ extern_methods!(
         #[method(frame)]
         pub(crate) fn frame(&self) -> NSRect;
 
+        #[method(windowNumber)]
+        pub(crate) fn windowNumber(&self) -> NSInteger;
+
         #[method(backingScaleFactor)]
         pub(crate) fn backingScaleFactor(&self) -> CGFloat;
 

src/platform_impl/macos/ffi.rs

@@ -2,6 +2,7 @@
 
 #![allow(dead_code, non_snake_case, non_upper_case_globals)]
 
+use objc2::{ffi::NSInteger, runtime::AnyObject};
 use std::ffi::c_void;
 
 use core_foundation::{
@@ -113,6 +114,14 @@ extern "C" {
     pub fn CGDisplayModeCopyPixelEncoding(mode: CGDisplayModeRef) -> CFStringRef;
     pub fn CGDisplayModeRetain(mode: CGDisplayModeRef);
     pub fn CGDisplayModeRelease(mode: CGDisplayModeRef);
+
+    // Wildly used private APIs, even Apple uses them for their Terminal.app.
+    pub fn CGSMainConnectionID() -> *mut AnyObject;
+    pub fn CGSSetWindowBackgroundBlurRadius(
+        connection_id: *mut AnyObject,
+        window_id: NSInteger,
+        radius: i64,
+    ) -> i32;
 }
 
 mod core_video {

src/platform_impl/macos/window.rs

@@ -46,6 +46,8 @@ use super::appkit::{
     NSView, NSWindow, NSWindowButton, NSWindowLevel, NSWindowSharingType, NSWindowStyleMask,
     NSWindowTabbingMode, NSWindowTitleVisibility,
 };
+use super::ffi::CGSMainConnectionID;
+use super::ffi::CGSSetWindowBackgroundBlurRadius;
 
 pub(crate) struct Window {
     window: MainThreadBound<Id<WinitWindow>>,
@@ -494,6 +496,10 @@ impl WinitWindow {
             this.setBackgroundColor(&NSColor::clear());
         }
 
+        if attrs.blur {
+            this.set_blur(attrs.blur);
+        }
+
         if let Some(dim) = attrs.min_inner_size {
             this.set_min_inner_size(Some(dim));
         }
@@ -582,7 +588,15 @@ impl WinitWindow {
         self.setOpaque(!transparent)
     }
 
-    pub fn set_blur(&self, _blur: bool) {}
+    pub fn set_blur(&self, blur: bool) {
+        // NOTE: in general we want to specify the blur radius, but the choice of 80
+        // should be a reasonable default.
+        let radius = if blur { 80 } else { 0 };
+        let window_number = self.windowNumber();
+        unsafe {
+            CGSSetWindowBackgroundBlurRadius(CGSMainConnectionID(), window_number, radius);
+        }
+    }
 
     pub fn set_visible(&self, visible: bool) {
         match visible {

src/window.rs

@@ -918,7 +918,7 @@ impl Window {
     ///
     /// ## Platform-specific
     ///
-    /// - **Android / iOS / macOS / X11 / Web / Windows:** Unsupported.
+    /// - **Android / iOS / X11 / Web / Windows:** Unsupported.
     /// - **Wayland:** Only works with org_kde_kwin_blur_manager protocol.
     #[inline]
     pub fn set_blur(&self, blur: bool) {