Game Programming using Qt 5 Beginner's Guide - Second Edition

The item's coordinate system

Each item has its own coordinate system. In our example of Post-it notes, the content of each note is defined relative to the top-left corner of the note. No matter how you move or rotate the item, these coordinates remain the same. The coordinates of a drawn object can usually be passed to the constructor of the class, like we did in our demo project, or to a special setter function (for example, rectItem->setRect(0, 10, 20, 25)). These are coordinates in the item's coordinate system.

Some classes, such as QGraphicsSimpleTextItem, do not provide the ability to change the coordinates of the content, so they're always positioned at the origin of the item's coordinate system. This is not a problem at all; as we'll ...