1 files changed, 49 insertions, 0 deletions
diff --git a/helix-event/src/redraw.rs b/helix-event/src/redraw.rs
new file mode 100644
index 00000000..a9915223
--- /dev/null
+++ b/helix-event/src/redraw.rs
@@ -0,0 +1,49 @@
+//! Signals that control when/if the editor redraws
+
+use std::future::Future;
+
+use parking_lot::{RwLock, RwLockReadGuard};
+use tokio::sync::Notify;
+
+/// A `Notify` instance that can be used to (asynchronously) request
+/// the editor the render a new frame.
+static REDRAW_NOTIFY: Notify = Notify::const_new();
+
+/// A `RwLock` that prevents the next frame from being
+/// drawn until an exclusive (write) lock can be acquired.
+/// This allows asynchsonous tasks to acquire `non-exclusive`
+/// locks (read) to prevent the next frame from being drawn
+/// until a certain computation has finished.
+static RENDER_LOCK: RwLock<()> = RwLock::new(());
+
+pub type RenderLockGuard = RwLockReadGuard<'static, ()>;
+
+/// Requests that the editor is redrawn. The redraws are debounced (currently to
+/// 30FPS) so this can be called many times without causing a ton of frames to
+/// be rendered.
+pub fn request_redraw() {
+    REDRAW_NOTIFY.notify_one();
+}
+
+/// Returns a future that will yield once a redraw has been asynchronously
+/// requested using [`request_redraw`].
+pub fn redraw_requested() -> impl Future<Output = ()> {
+    REDRAW_NOTIFY.notified()
+}
+
+/// Wait until all locks acquired with [`lock_frame`] have been released.
+/// This function is called before rendering and is intended to allow the frame
+/// to wait for async computations that should be included in the current frame.
+pub fn start_frame() {
+    drop(RENDER_LOCK.write());
+    // exhaust any leftover redraw notifications
+    let notify = REDRAW_NOTIFY.notified();
+    tokio::pin!(notify);
+    notify.enable();
+}
+
+/// Acquires the render lock which will prevent the next frame from being drawn
+/// until the returned guard is dropped.
+pub fn lock_frame() -> RenderLockGuard {
+    RENDER_LOCK.read()
+}