Use set interval setting to fix performance degration for AMD graphics adapters

src/widget/openglwindow.cpp

@@ -14,6 +14,29 @@ OpenGLWindow::OpenGLWindow(WGLWidget* pWidget)
     QSurfaceFormat format;
     format.setVersion(2, 1);
     format.setProfile(QSurfaceFormat::CoreProfile);
+
+    // setSwapInterval sets the application preferred swap interval
+    // in minimum number of video frames that are displayed before a buffer swap occurs
+    // - 0 will turn the vertical refresh syncing off
+    // - 1 (default) means swapping after drawig a video frame to the buffer
+    // - n means swapping after drawing n video frames to the buffer
+    //
+    // The vertical sync setting requested by the OpenGL application, can be overwritten
+    // if a user changes the "Wait for vertical refresh" setting in AMD graphic drivers
+    // for Windows.
+
+#if defined(__APPLE__)
+    // On OS X, syncing to vsync has good performance FPS-wise and
+    // eliminates tearing. (This is an comment from pre QOpenGLWindow times)
+    format.setSwapInterval(1);
+#else
+    // It seems that on Windows (at least for some AMD drivers), the setting 1 is not
+    // not properly handled. We saw frame rates divided by exact integers, like it should
+    // be with values >1 (see https://github.com/mixxxdj/mixxx/issues/11617)
+    // Reported as https://bugreports.qt.io/browse/QTBUG-114882
+    // On Linux, horrible FPS were seen with "VSync off" before switching to QOpenGLWindow too
+    format.setSwapInterval(0);
+#endif
     setFormat(format);
 }