Add an option to disable VST3 content scaling

This might be necessary when using a HiDPI screen as plugin GUIs often
don't scale correctly under Wine.

src/common/configuration.cpp

@@ -113,6 +113,12 @@ Configuration::Configuration(const fs::path& config_path,
                 } else {
                     invalid_options.push_back(key);
                 }
+            } else if (key == "vst3_no_scaling") {
+                if (const auto parsed_value = value.as_boolean()) {
+                    vst3_no_scaling = parsed_value->get();
+                } else {
+                    invalid_options.push_back(key);
+                }
             } else {
                 unknown_options.push_back(key);
             }

src/common/configuration.h

@@ -122,6 +122,15 @@ class Configuration {
      */
     std::optional<float> frame_rate;
 
+    /**
+     * Disable `IPlugViewContentScaleSupport::setContentScaleFactor()`. Wine
+     * does not properly implement DPI scaling, so without this option plugins
+     * using GDI+ would draw their editor GUIs at the normal size even though
+     * their window would actually be scaled. That would result in giant black
+     * borders at the top and the right of the window.
+     */
+    bool vst3_no_scaling = false;
+
     /**
      * The name of the plugin group that should be used for the plugin this
      * configuration object was created for. If not set, then the plugin should
@@ -165,6 +174,7 @@ class Configuration {
         s.value1b(editor_xembed);
         s.ext(frame_rate, bitsery::ext::StdOptional(),
               [](S& s, auto& v) { s.value4b(v); });
+        s.value1b(vst3_no_scaling);
         s.ext(group, bitsery::ext::StdOptional(),
               [](S& s, auto& v) { s.text1b(v, 4096); });