T23: the owner's checks on macOS: on macOS 27 gpui's Selection material drew no blur, so blur/macos gives the window's effect view underWindowBackground, radius 30; a button at each end of the title bar hides and shows its column, kept in the settings; shot reads an effect view's blur radius; new comments cut to ten words

src/blur/macos.rs

@@ -0,0 +1,50 @@
+use anyhow::bail;
+use gpui::Window;
+use objc::{
+    class, msg_send,
+    runtime::{BOOL, Object, YES},
+    sel, sel_impl,
+};
+use raw_window_handle::{HasWindowHandle, RawWindowHandle};
+
+/// `NSVisualEffectMaterialUnderWindowBackground`.
+const UNDER_WINDOW_BACKGROUND: isize = 21;
+
+/// Gives gpui's effect view a blurring material; logs either way.
+pub fn blur(window: &Window) {
+    match effect_view(window) {
+        Ok(view) => {
+            unsafe {
+                let _: () = msg_send![view, setMaterial: UNDER_WINDOW_BACKGROUND];
+            }
+            log::info!(
+                "blur: the window's NSVisualEffectView takes underWindowBackground; gpui's Selection material draws no blur on macOS 27"
+            );
+        }
+        Err(error) => log::error!("blur: the window does not blur: {error:#}"),
+    }
+}
+
+/// The NSVisualEffectView gpui puts under the window's content for `Blurred`.
+fn effect_view(window: &Window) -> anyhow::Result<*mut Object> {
+    let handle = HasWindowHandle::window_handle(window)
+        .map_err(|error| anyhow::anyhow!("no native handle: {error:?}"))?;
+    let RawWindowHandle::AppKit(appkit) = handle.as_raw() else {
+        bail!("not an AppKit window");
+    };
+    unsafe {
+        let view = appkit.ns_view.as_ptr() as *mut Object;
+        let native: *mut Object = msg_send![view, window];
+        let content: *mut Object = msg_send![native, contentView];
+        let views: *mut Object = msg_send![content, subviews];
+        let count: usize = msg_send![views, count];
+        for ix in 0..count {
+            let view: *mut Object = msg_send![views, objectAtIndex: ix];
+            let effect: BOOL = msg_send![view, isKindOfClass: class!(NSVisualEffectView)];
+            if effect == YES {
+                return Ok(view);
+            }
+        }
+    }
+    bail!("gpui put no NSVisualEffectView under the content")
+}