Downscale Images to document resolution (#1077)

* Add DownscaleNode

* Add lambda (call argument) input type + fix caching

* Add comment explaining Lambda input

* Automatically insert cache node after downscale node

* Implement sparse hashing of images

node-graph/gstd/src/memo.rs

@@ -6,14 +6,18 @@ use graphene_core::Node;
 
 /// Caches the output of a given Node and acts as a proxy
 #[derive(Default)]
-pub struct CacheNode<T> {
+pub struct CacheNode<T, CachedNode> {
 	// We have to use an append only data structure to make sure the references
 	// to the cache entries are always valid
 	cache: boxcar::Vec<(u64, T)>,
+	node: CachedNode,
 }
-impl<'i, T: 'i + Hash> Node<'i, T> for CacheNode<T> {
+impl<'i, T: 'i, I: 'i + Hash, CachedNode: 'i> Node<'i, I> for CacheNode<T, CachedNode>
+where
+	CachedNode: for<'any_input> Node<'any_input, I, Output = T>,
+{
 	type Output = &'i T;
-	fn eval<'s: 'i>(&'s self, input: T) -> Self::Output {
+	fn eval<'s: 'i>(&'s self, input: I) -> Self::Output {
 		let mut hasher = Xxh3::new();
 		input.hash(&mut hasher);
 		let hash = hasher.finish();
@@ -22,15 +26,16 @@ impl<'i, T: 'i + Hash> Node<'i, T> for CacheNode<T> {
 			return cached_value;
 		} else {
 			trace!("Cache miss");
-			let index = self.cache.push((hash, input));
+			let output = self.node.eval(input);
+			let index = self.cache.push((hash, output));
 			return &self.cache[index].1;
 		}
 	}
 }
 
-impl<T> CacheNode<T> {
-	pub fn new() -> CacheNode<T> {
-		CacheNode { cache: boxcar::Vec::new() }
+impl<T, CachedNode> CacheNode<T, CachedNode> {
+	pub fn new(node: CachedNode) -> CacheNode<T, CachedNode> {
+		CacheNode { cache: boxcar::Vec::new(), node }
 	}
 }