Filter Win32 windows for XDND by class name

Instead of ignoring all windows that have an associated X11 window. That
would otherwise treat standalone applications like yabridge GUI
wrappers.

CHANGELOG.md

@@ -13,6 +13,14 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 - Added more tracing for input focus handling when using the `+editor`
   `YABRIDGE_DEBUG_LEVEL` flag.
 
+### Fixed
+
+- Changed the filter in the Wine->X11 drag-and-drop implementation for
+  distinguishing between Wine windows and other windows (so that we don't
+  interfere with Wine->Wine drag-and-drop) to be more specific. Before this
+  change we might use our own XDND implementation when dragging from a plugin to
+  a standalone Wine application running within the same Wine prefix.
+
 ## [3.5.0] - 2021-06-23
 
 ### Added

src/wine-host/editor.cpp

@@ -44,7 +44,7 @@ using namespace std::literals::string_literals;
  * The name of the Win32 window class we'll use for the Win32 window that the
  * plugin can embed itself in.
  */
-constexpr char window_class_name[] = "yabridge plugin";
+constexpr char yabridge_window_class_name[] = "yabridge plugin";
 
 /**
  * The Win32 timer ID we'll use to periodically call the VST2 `effeditidle`
@@ -1237,7 +1237,7 @@ ATOM get_window_class() noexcept {
         window_class.lpfnWndProc = window_proc;
         window_class.hInstance = GetModuleHandle(nullptr);
         window_class.hCursor = arrow_cursor;
-        window_class.lpszClassName = window_class_name;
+        window_class.lpszClassName = yabridge_window_class_name;
 
         window_class_handle = RegisterClassEx(&window_class);
     }
@@ -1252,19 +1252,18 @@ bool is_cursor_in_wine_window() noexcept {
     GetCursorPos(&windows_pointer_pos);
     if (HWND windows_window = WindowFromPoint(windows_pointer_pos);
         windows_window && windows_window != windows_desktop_window) {
-        // NOTE: Because resizing reparented Wine windows without XEmbed is
+        // NOTE: Because resizing reparented Wine windows without XEmbed is a
-        //       a bit janky, yabridge creates windows with client areas
+        //       bit janky, yabridge creates windows with client areas large
-        //       large enough to fit the entire screen, and the plugin then
+        //       enough to fit the entire screen, and the plugin then embeds its
-        //       embeds its own GUI in a portion of that. The result is that
+        //       own GUI in a portion of that. The result is that
         //       `WindowFromPoint()` will still return that same huge window
-        //       when we hover over an area to the right or to the bottom of
+        //       when we hover over an area to the right or to the bottom of a
-        //       a plugin GUI. We can easily detect and skip that though,
+        //       plugin GUI. We can easily detect by just checking the window
-        //       since the embedded plugin windows won't have an X11 window
+        //       class name.
-        //       ID property.
+        std::array<char, 64> window_class_name{0};
-        const xcb_window_t x11_window =
+        GetClassName(windows_window, window_class_name.data(),
-            static_cast<xcb_window_t>(reinterpret_cast<size_t>(
+                     window_class_name.size());
-                GetProp(windows_window, "__wine_x11_whole_window")));
+        if (strcmp(window_class_name.data(), yabridge_window_class_name) != 0) {
-        if (x11_window == XCB_NONE) {
             return true;
         }
     }