utils: add DoubleBuffered

src/utils.rs

@@ -12,6 +12,7 @@ pub mod clone3;
 pub mod clonecell;
 pub mod copyhashmap;
 pub mod debug_fn;
+pub mod double_buffered;
 pub mod double_click_state;
 pub mod errorfmt;
 pub mod event_listener;

src/utils/double_buffered.rs

@@ -0,0 +1,40 @@
+use std::{cell::Cell, ops::Deref};
+
+#[derive(Default)]
+pub struct DoubleBuffered<T> {
+    bufs: [T; 2],
+    front: Cell<usize>,
+}
+
+impl<T> DoubleBuffered<T> {
+    #[expect(dead_code)]
+    pub fn new(bufs: [T; 2]) -> Self {
+        Self {
+            bufs,
+            front: Cell::new(0),
+        }
+    }
+
+    #[expect(dead_code)]
+    pub fn front(&self) -> &T {
+        unsafe { self.bufs.get_unchecked(self.front.get()) }
+    }
+
+    #[expect(dead_code)]
+    pub fn back(&self) -> &T {
+        unsafe { self.bufs.get_unchecked(1 - self.front.get()) }
+    }
+
+    #[expect(dead_code)]
+    pub fn flip(&self) {
+        self.front.set(1 - self.front.get());
+    }
+}
+
+impl<T> Deref for DoubleBuffered<T> {
+    type Target = [T; 2];
+
+    fn deref(&self) -> &Self::Target {
+        &self.bufs
+    }
+}