The app icon in Ubuntu Bionic Dock and GNOME Activities Favorites (e.g., Fedora 29) looks ugly due to improper scaling (screenshots).

There are some possible solutions:

1. Qt::SmoothTransformation does not work as expected (qt: Use bilinear filtering for icon #14990)

2. Multiple QPixmaps added by QIcon::addPixmap() do not work in this case (qt: Use bilinear filtering for icon #14990 (comment); Qt bug?)

3. Use SVG images as icons directly

An icon engine that supports SVG is included with Qt since version 4.2 (tested: it works).