What's the equivalent c++ code for border-radius in qss?

[Sauntor]

You can set the border radius for a QWidget with stylesheet:

border-radius: 6px;

but if you want implement it only using c++ ( no setStylesheet() ), it find out to be too complicated(, on my opinion)!
so, is there a simple to achieve it?
or on the other hand, can we achieve it by using QProxyStyle without reimplementing many draw*() functions?

[Pl45m4]

@Sauntor

Use the paint() event of your QWidget and draw your custom shape, like drawRoundedRect()