VST3: Fix making plugin windows larger not working in Carla

Fixes making VST3 plugins larger than their original size in Carla. The
plugin would resize but not get drawn past the original window size.

src/wine-host/bridges/vst3-impls/plug-frame-proxy.cpp

@@ -52,8 +52,18 @@ Vst3PlugFrameProxyImpl::resizeView(Steinberg::IPlugView* /*view*/,
         // We have to use this special sending function here so we can handle
         // calls to `IPlugView::onSize()` from this same thread (the UI thread).
         // See the docstring for more information.
-        return bridge_.send_mutually_recursive_message(YaPlugFrame::ResizeView{
+        const tresult result =
+            bridge_.send_mutually_recursive_message(YaPlugFrame::ResizeView{
                 .owner_instance_id = owner_instance_id(), .new_size = *newSize});
+
+        // Some hosts (like Carla) don't call onSize() after accepting a
+        // resizeView() request. This causes the plugin to not know about its
+        // new size, so it doesn't draw beyond the original size. Call the
+        // plugin's onSize() ourselves to ensure it knows the new size. If the
+        // host already called onSize(), this will be a harmless duplicate call.
+        bridge_.notify_plugin_on_new_size(owner_instance_id(), *newSize);
+
+        return result;
     } else {
         std::cerr
             << "WARNING: Null pointer passed to 'IPlugFrame::resizeView()'"

src/wine-host/bridges/vst3.cpp

@@ -1388,6 +1388,26 @@ bool Vst3Bridge::resize_editor(size_t instance_id,
     }
 }
 
+void Vst3Bridge::notify_plugin_on_new_size(size_t instance_id,
+                                           Steinberg::ViewRect& new_size) {
+    const auto& [instance, _] = get_instance(instance_id);
+
+    if (instance.plug_view_instance) {
+        // Skip if the host already called onSize() with this size during
+        // resizeView(). This is detected by checking if last_set_size already
+        // matches new_size (the OnSize handler updates last_set_size).
+        if (instance.last_set_size.getWidth() == new_size.getWidth() &&
+            instance.last_set_size.getHeight() == new_size.getHeight()) {
+            return;
+        }
+
+        instance.plug_view_instance->plug_view->onSize(&new_size);
+
+        // Update last_set_size so getSize() returns consistent values
+        instance.last_set_size = new_size;
+    }
+}
+
 void Vst3Bridge::register_context_menu(Vst3ContextMenuProxyImpl& context_menu) {
     const auto& [owner_instance, _] =
         get_instance(context_menu.owner_instance_id());

src/wine-host/bridges/vst3.h

@@ -318,6 +318,14 @@ class Vst3Bridge : public HostBridge {
      */
     bool resize_editor(size_t instance_id, const Steinberg::ViewRect& new_size);
 
+    /**
+     * Notify the plugin of its new size by calling `IPlugView::onSize()`.
+     * This is called after `resize_editor()` for hosts that don't call
+     * `onSize()` after accepting a `resizeView()` request (like Carla).
+     */
+    void notify_plugin_on_new_size(size_t instance_id,
+                                   Steinberg::ViewRect& new_size);
+
     /**
      * Register a context with with `context_menu`'s ID and owner in
      * `object_instances`. This will be called during the constructor of