diff --git a/src/app.rs b/src/app.rs
index 1fc43d8..5b66bd3 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -715,15 +715,3 @@ fn draw_grid(mesh: &mut Mesh, grid: &Array2D<GridCell>) {
     }
 }
 */
-
-fn nodegraph_fn_inputs() -> ParameterList {
-    use vorpal_widgets::vorpal_core::{DataType, ExternInputId};
-    let params = [
-        (ExternInputId::new("time".to_string()), DataType::Scalar),
-        (ExternInputId::new("position".to_string()), DataType::Vec2),
-    ]
-    .into_iter()
-    .collect();
-
-    ParameterList(params)
-}
diff --git a/src/sim.rs b/src/sim.rs
index 12015e8..44f5e91 100644
--- a/src/sim.rs
+++ b/src/sim.rs
@@ -5,7 +5,7 @@ use crate::query_accel::QueryAccelerator;
 
 use glam::Vec2;
 use rand::prelude::*;
-use vorpal_widgets::vorpal_core::{ExternParameters, ExternInputId, Value};
+use vorpal_widgets::vorpal_core::{ExternParameters, ExternInputId, Value, ParameterList, DataType};
 use vorpal_widgets::vorpal_core::{Node, native_backend::evaluate_node};
 
 #[derive(Clone)]
@@ -695,7 +695,7 @@ fn node_interactions(particles: &mut [Particle], node: &Rc<Node>, cfg: &NodeInte
     for i in 0..particles.len() {
         for neighbor in accel.query_neighbors_fast(i, points[i]) {
             // The vector pointing from a to b
-            let diff = points[i] - points[neighbor];
+            let diff = points[neighbor] - points[i];
 
             let inputs = [
                 (ExternInputId::new("neigh-radius".into()), Value::Scalar(cfg.neighbor_radius)),
@@ -709,3 +709,14 @@ fn node_interactions(particles: &mut [Particle], node: &Rc<Node>, cfg: &NodeInte
     }
 
 }
+
+pub fn nodegraph_fn_inputs() -> ParameterList {
+    let params = [
+        (ExternInputId::new("neigh-radius".to_string()), DataType::Scalar),
+        (ExternInputId::new("pos-diff".to_string()), DataType::Vec2),
+    ]
+    .into_iter()
+    .collect();
+
+    ParameterList(params)
+}