metal: simplify framebuffer swapchain

src/utils/opaque_cell.rs

@@ -0,0 +1,28 @@
+use std::{
+    cell::Cell,
+    fmt::{Debug, Formatter},
+    ops::{Deref, DerefMut},
+};
+
+#[derive(Default)]
+pub struct OpaqueCell<T>(Cell<T>);
+
+impl<T> Deref for OpaqueCell<T> {
+    type Target = Cell<T>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<T> DerefMut for OpaqueCell<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.0
+    }
+}
+
+impl<T> Debug for OpaqueCell<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "Cell<{}> {{ ... }}", std::any::type_name::<T>())
+    }
+}