Disable blitting on window position changes

This slightly reduces flickering because redraws are now a bit faster.

CHANGELOG.md

@@ -36,6 +36,9 @@ TODO: Add an updates screenshot with some fancy VST3-only plugins to the readme
 - `libyabridge.so` is now called `libyabridge-vst2.so`. If you're using
   yabridgectl then nothing changes here. **To avoid any confusion in the future,
   please remove the old `libyabridge.so` file before upgrading.**
+- Slightly increased resposniveness when resizing plugin GUIs by preventing
+  unnecessary blitting. This also reduces flickering with plugins that don't do
+  double buffering.
 - VST2 editor idle events are now handled slightly differently. This should
   result in even more responsive GUIs and I have not come across any plugins
   where this caused issues, but please let me know if it does break anything for

src/wine-host/editor.cpp

@@ -97,8 +97,8 @@ WindowClass::~WindowClass() {
 Editor::Editor(const Configuration& config,
                const std::string& window_class_name,
                const size_t parent_window_handle)
-    : x11_connection(xcb_connect(nullptr, nullptr), xcb_disconnect),
-      use_xembed(config.editor_xembed),
+    : use_xembed(config.editor_xembed),
+      x11_connection(xcb_connect(nullptr, nullptr), xcb_disconnect),
       client_area(get_maximum_screen_dimensions(*x11_connection)),
       window_class(window_class_name),
       // Create a window without any decoratiosn for easy embedding. The
@@ -540,6 +540,19 @@ LRESULT CALLBACK window_proc(HWND handle,
             SetWindowLongPtr(handle, GWLP_USERDATA,
                              reinterpret_cast<size_t>(editor));
         } break;
+        // Setting `SWP_NOCOPYBITS` somewhat reduces flickering on
+        // `fix_local_coordinates()` calls with plugins that don't do double
+        // buffering since it speeds up the redrawing process.
+        case WM_WINDOWPOSCHANGING: {
+            auto editor = reinterpret_cast<Editor*>(
+                GetWindowLongPtr(handle, GWLP_USERDATA));
+            if (!editor || editor->use_xembed) {
+                break;
+            }
+
+            WINDOWPOS* info = reinterpret_cast<WINDOWPOS*>(lParam);
+            info->flags |= SWP_NOCOPYBITS | SWP_DEFERERASE;
+        } break;
         // In case the WM does not support the EWMH active window property,
         // we'll fall back to grabbing focus when the user clicks on the window
         // by listening to the generated `WM_PARENTNOTIFY` messages. Otherwise

src/wine-host/editor.h

@@ -151,6 +151,12 @@ class Editor {
      */
     void set_input_focus(bool grab) const;
 
+    /**
+     * Whether to use XEmbed instead of yabridge's normal window embedded. Wine
+     * with XEmbed tends to cause rendering issues, so it's disabled by default.
+     */
+    const bool use_xembed;
+
    private:
     /**
      * Returns `true` if the currently active window (as per
@@ -185,12 +191,6 @@ class Editor {
      */
     std::unique_ptr<xcb_connection_t, decltype(&xcb_disconnect)> x11_connection;
 
-    /**
-     * Whether to use XEmbed instead of yabridge's normal window embedded. Wine
-     * with XEmbed tends to cause rendering issues, so it's disabled by default.
-     */
-    const bool use_xembed;
-
     /**
      * The Wine window's client area, or the maximum size of that window. This
      * will be set to a size that's large enough to be able to enter full screen