We added transparency support in Qt 4.5 through the Qt::WA_TranslucentBackground attribute. Unfortunately, as documented, it will only work on Windows if you explicitly remove window decorations.
With Windows Vista, Microsoft introduced the DWM (Desktop Window Manager) api, where you can enable a blur effect behind your application window. Unfortunately Qt does not have API to cover this yet, but by using the aforementioned translucent attribute in combination with a few native API calls you can already get this effect with Qt 4.5.
To make it simple, I created a convenience API to handle it so you can
plug it into your existing code. Note that the code should compile fine on other
platforms as well:
bool QtWin::enableBlurBehindWindow(QWidget *widget, bool enable)
bool QtWin::extendFrameIntoClientArea(QWidget *widget, int left, int top, int right, int bottom)
You can make a widget blurry by calling enableBlurBehindWindow or extendFrameIntoClientArea with the preferred margins. In both cases you are simply modifying the background of the widget. The colorizationColor is the color Windows tints the window with.
To show of the effect I made (yet another!) 200-line Qt browser. It has a custom style sheet with semi-transparent widgets. You will also see how you can make segmented arrow buttons using nothing but a pair of style sheets.
You can get the code and executables here.
Happy coding! 🙂