Allow viewer co customize egui style for the individual node UI

src/ui.rs

@@ -1597,6 +1597,10 @@ impl<T> Snarl<T> {
         let mut new_pins_size = Vec2::ZERO;
 
         let r = node_frame.show(node_ui, |ui| {
+            if viewer.has_node_style(node, &inputs, &outputs, self) {
+                viewer.apply_node_style(ui.style_mut(), node, &inputs, &outputs, self);
+            }
+
             let min_pin_y = node_state.header_height().mul_add(0.5, node_rect.min.y);
 
             // Input pins' center side by X axis.

src/ui/viewer.rs

@@ -37,6 +37,30 @@ pub trait SnarlViewer<T> {
         let _ = (node, inputs, outputs, snarl);
         default
     }
+    /// Checks if node has a custom egui style.
+    #[inline]
+    fn has_node_style(
+        &mut self,
+        node: NodeId,
+        inputs: &[InPin],
+        outputs: &[OutPin],
+        snarl: &Snarl<T>,
+    ) -> bool {
+        let _ = (node, inputs, outputs, snarl);
+        false
+    }
+
+    /// Modifies the node's egui style
+    fn apply_node_style(
+        &mut self,
+        style: &mut Style,
+        node: NodeId,
+        inputs: &[InPin],
+        outputs: &[OutPin],
+        snarl: &Snarl<T>,
+    ) {
+        let _ = (style, node, inputs, outputs, snarl);
+    }
 
     /// Returns layout override for the node.
     ///