QIconEngine has no access to the devicePixelRatio

The QIconEngine has no way to access the devicePixelRatio of a requested pixmap for an icon. QIcon::pixmap() just requests a larger pixmap from the QIconEngine.

For instance, a 16x16 icon is typically less detailed (eg. in case of a "Music folder" it would just show a note rather than a folder with a note) but since a 32x32 pixmap will be requested without any information on what size the eventual physical display will be, the QIconEngine will return a more detailed pixmap which then has the same physical size as the 16x16 on a low dpi screen and thus is hard do recognize due to its small details.

It is perfectly fine to request a larger pixmap but when you provide a custom icon engine you should be able to distinguish between "legitimate 32x32 request" or "16x16 request at double size" so you can act accordingly, especially when it's an SVG icon theme.