Compile node graph description to GPU code

node-graph/gcore/src/value.rs

@@ -1,4 +1,6 @@
 use core::marker::PhantomData;
+use core::mem::MaybeUninit;
+use core::sync::atomic::AtomicBool;
 
 use crate::Node;
 
@@ -18,8 +20,7 @@ impl<'n, T: 'n> Node<'n> for ValueNode<T> {
         &self.0
     }
 }
-
-impl<'n, T> ValueNode<T> {
+impl<T> ValueNode<T> {
     pub const fn new(value: T) -> ValueNode<T> {
         ValueNode(value)
     }
@@ -33,8 +34,29 @@ impl<'n, T: Default + 'n> Node<'n> for DefaultNode<T> {
         T::default()
     }
 }
-impl<T> DefaultNode<T> {
-    pub const fn new() -> DefaultNode<T> {
-        DefaultNode(PhantomData)
+
+#[repr(C)]
+/// Return the unit value
+pub struct UnitNode;
+impl<'n> Node<'n> for UnitNode {
+    type Output = ();
+    fn eval(&'n self) -> Self::Output {}
+}
+
+pub struct InputNode<T>(MaybeUninit<T>, AtomicBool);
+impl<'n, T: 'n> Node<'n> for InputNode<T> {
+    type Output = &'n T;
+    fn eval(&'n self) -> Self::Output {
+        if self.1.load(core::sync::atomic::Ordering::SeqCst) {
+            unsafe { self.0.assume_init_ref() }
+        } else {
+            panic!("tried to access an input before setting it")
+        }
+    }
+}
+
+impl<T> InputNode<T> {
+    pub const fn new() -> InputNode<T> {
+        InputNode(MaybeUninit::uninit(), AtomicBool::new(false))
     }
 }