Toolbar icons are blurry on Windows if the devicePixelRatio is set higher than 1. Attached image shows this.

Steps to reprocude:

• Set QT_DEVICE_PIXEL_RATIO environment variable to 2 and launch the Main Window example, http://doc.qt.io/qt-5/qtwidgets-mainwindows-mainwindow-example.html
• EXPECTED: Icons in toolbar are sharp (like other images in the application)
• ACTUAL: Icons in toolbar are blurry