rendering code and api crate

crates/bevy_xr/src/session.rs

@@ -0,0 +1,89 @@
+use bevy::app::{App, Plugin, PreUpdate};
+use bevy::ecs::event::{Event, EventReader, EventWriter};
+use bevy::ecs::system::Local;
+
+pub struct XrSessionPlugin;
+
+impl Plugin for XrSessionPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_event::<CreateXrSession>()
+            .add_event::<BeginXrSession>()
+            .add_event::<EndXrSession>()
+            .add_event::<XrSessionState>()
+            .add_event::<XrInstanceCreated>()
+            .add_event::<XrInstanceDestroyed>()
+            .add_systems(PreUpdate, handle_xr_events);
+    }
+}
+
+pub fn handle_xr_events(
+    mut instance_created: EventReader<XrInstanceCreated>,
+    mut session_state: EventReader<XrSessionState>,
+    mut instance_destroyed: EventReader<XrInstanceDestroyed>,
+    mut create_session: EventWriter<CreateXrSession>,
+    mut begin_session: EventWriter<BeginXrSession>,
+    mut has_instance: Local<bool>,
+    mut local_session_state: Local<Option<XrSessionState>>,
+) {
+    // Don't do anything if no events recieved
+    if instance_created.is_empty() && instance_destroyed.is_empty() && session_state.is_empty() {
+        return;
+    }
+    if !instance_created.is_empty() {
+        *has_instance = true;
+        instance_created.clear();
+    }
+    if !instance_destroyed.is_empty() {
+        *has_instance = false;
+        instance_destroyed.clear();
+    }
+    for state in session_state.read() {
+        *local_session_state = Some(*state);
+    }
+    if *has_instance {
+        if local_session_state.is_none() {
+            create_session.send_default();
+        } else if matches!(*local_session_state, Some(XrSessionState::Ready)) {
+            begin_session.send_default();
+        }
+    }
+}
+
+/// Event sent to backends to create an XR session
+#[derive(Event, Clone, Copy, Default)]
+pub struct CreateXrSession;
+
+/// Event sent to backends to begin an XR session
+#[derive(Event, Clone, Copy, Default)]
+pub struct BeginXrSession;
+
+/// Event sent to backends to end an XR session.
+#[derive(Event, Clone, Copy, Default)]
+pub struct EndXrSession;
+
+// /// Event sent to backends to destroy an XR session.
+// #[derive(Event, Clone, Copy, Default)]
+// pub struct DestroyXrSession;
+
+/// Event sent from backends to inform the frontend of the session state.
+#[derive(Event, Clone, Copy)]
+pub enum XrSessionState {
+    /// The session is in an idle state. Either just created or stopped
+    Idle,
+    /// The session is ready. You may send a [`BeginXrSession`] event.
+    Ready,
+    /// The session is running.
+    Running,
+    /// The session is being stopped
+    Stopping,
+    /// The session is destroyed
+    Destroyed,
+}
+
+/// Event sent from backends to inform the frontend that the instance was created.
+#[derive(Event, Clone, Copy, Default)]
+pub struct XrInstanceCreated;
+
+/// Event sent from backends to inform the frontend that the instance was destroyed.
+#[derive(Event, Clone, Copy, Default)]
+pub struct XrInstanceDestroyed;