Going via QWidget::grab() will render to a QPixmap, which on most platforms is going to be QRasterPlatformPixmap. The format of the underlying QImage in that case is resolved from the primary screen, which most platforms report as QImage::Format_RGB32. This means we will not be able to detect the difference between black and fully transparent areas in the rendered result, which has been observed to be a problem for widget styles that wrongly render their controls using source composition. To solve this we render via QWidget::render() instead, to an image with an alpha format. Change-Id: I078f062b662590598c3597797abc2bfa78eaf86a Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>