Convert a SVG image to QPixmap format is a very easy operation using the Qt classes. Common examples that is possible to find into documentation, however, refer to a situation where the screen device have standard pixel ratio of 1.

If you want to develop a custom Qt widget to distrbute or sell a good habits is always to develop, in addition, a plugin working into Qt Designer allowing to visually use and configure your custom widget inside the designer GUI editor. Develop such plugin is not a difficult task, official documentation and examples are here and, as usual for Qt, all is well explained.
Another important task of software development is to create a good graphic elements for make the interface look better. Graphic texts, icons, logos and so on are all parts of a good product. If you, like me, are not so good in graphic design we need some help...

In case you are working with Qt Graphics View Framework you probably make use of the QGraphicsView method fitInView(). This function, based to the official documentation, scales the view matrix and scrolls the scroll bars to ensure that the scene rectangle rect fits inside the viewport. 

QGraphicsScene is a great Qt component allowing to develop full graphics applications (like game for example) in a very easy way. As additional feature is possible to insert a QWidget based object inside the scene through the QGraphicsProxyWidget item.