VST3: Add HiDPI scaling hack

Sometimes the plugin size might be off-by-one due to HiDPI scaling. If
so, pretend it's actually the size that was requested, to avoid ending
up in an infinite loop.

src/wine-host/bridges/vst3.cpp

@@ -899,8 +899,22 @@ void Vst3Bridge::run() {
                             get_instance(request.owner_instance_id);
                         std::lock_guard lock(instance.get_size_mutex);
 
-                        return instance.plug_view_instance->plug_view->getSize(
-                            &size);
+                        auto result =
+                            instance.plug_view_instance->plug_view->getSize(
+                                &size);
+                        // HACK: Sometimes, due to HiDPI scaling, plugins might
+                        //       end up with a size that is off by one pixel
+                        //       from the requested size. To avoid ending up in
+                        //       an infinite loop, just return the size that the
+                        //       host requested in this case.
+                        if (result == Steinberg::kResultOk &&
+                            abs(size.getWidth() -
+                                instance.last_set_size.getWidth()) <= 1 &&
+                            abs(size.getHeight() -
+                                instance.last_set_size.getHeight()) <= 1) {
+                            size = instance.last_set_size;
+                        }
+                        return result;
                     });
 
                 return YaPlugView::GetSizeResponse{.result = result,
@@ -934,6 +948,8 @@ void Vst3Bridge::run() {
                                                 request.new_size.getHeight());
                     }
 
+                    instance.last_set_size = request.new_size;
+
                     return result;
                 });
             },

src/wine-host/bridges/vst3.h

@@ -256,6 +256,14 @@ struct Vst3PluginInstance {
      * processing.
      */
     std::optional<Steinberg::Vst::ProcessSetup> process_setup;
+
+    /**
+     * The last size that was set with onSize(). We use this to fudge the
+     * return value of getSize() if it is off by one pixel, which can happen
+     * due to HiDPI rounding. Otherwise, DAWs like Ardour might go into an
+     * infinite loop trying to adjust the size to a specific target.
+     */
+    Steinberg::ViewRect last_set_size;
 };
 
 /**