Add build closure parameter to create_egui_editor

BREAKING_CHANGES.md

@@ -8,6 +8,8 @@ code then it will not be listed here.
 
 ## [2022-10-20]
 
+- The `create_egui_editor()` function from `nih_plug_egui` now also takes a
+  build closure to apply initialization logic to the egui context.
 - The `nih_plug::param` module has been renamed to `nih_plug::params`. Code that
   only uses the prelude module doesn't need to be changed.
 - Some items have been moved out of `nih_plug::param::internals`. The main

nih_plug_egui/src/lib.rs

@@ -35,18 +35,21 @@ pub mod widgets;
 /// field on your parameters struct.
 ///
 /// See [`EguiState::from_size()`].
-pub fn create_egui_editor<T, U>(
+pub fn create_egui_editor<T, B, U>(
     egui_state: Arc<EguiState>,
     user_state: T,
+    build: B,
     update: U,
 ) -> Option<Box<dyn Editor>>
 where
     T: 'static + Send + Sync,
+    B: Fn(&Context, &mut T) + 'static + Send + Sync,
     U: Fn(&Context, &ParamSetter, &mut T) + 'static + Send + Sync,
 {
     Some(Box::new(EguiEditor {
         egui_state,
         user_state: Arc::new(RwLock::new(user_state)),
+        build: Arc::new(build),
         update: Arc::new(update),
 
         // TODO: We can't get the size of the window when baseview does its own scaling, so if the
@@ -110,6 +113,9 @@ struct EguiEditor<T> {
     egui_state: Arc<EguiState>,
     /// The plugin's state. This is kept in between editor openenings.
     user_state: Arc<RwLock<T>>,
+
+    /// The user's build function. Applied once at the start of the application.
+    build: Arc<dyn Fn(&Context, &mut T) + 'static + Send + Sync>,
     /// The user's update function.
     update: Arc<dyn Fn(&Context, &ParamSetter, &mut T) + 'static + Send + Sync>,
 
@@ -127,6 +133,7 @@ where
         parent: ParentWindowHandle,
         context: Arc<dyn GuiContext>,
     ) -> Box<dyn std::any::Any + Send + Sync> {
+        let build = self.build.clone();
         let update = self.update.clone();
         let state = self.user_state.clone();
 
@@ -161,7 +168,7 @@ where
                 }),
             },
             state,
-            |_, _, _| {},
+            move |egui_ctx, _queue, state| build(egui_ctx, &mut state.write()),
             move |egui_ctx, _queue, state| {
                 let setter = ParamSetter::new(context.as_ref());
 

plugins/examples/gain_gui_egui/src/lib.rs

@@ -93,6 +93,7 @@ impl Plugin for Gain {
         create_egui_editor(
             self.params.editor_state.clone(),
             (),
+            |_, _| {},
             move |egui_ctx, setter, _state| {
                 egui::CentralPanel::default().show(egui_ctx, |ui| {
                     // NOTE: See `plugins/diopser/src/editor.rs` for an example using the generic UI widget