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

Time for action – Making oscillograms selectable

It's time to make our oscillogram widget interactive. We will teach it to add a couple of lines of code to it that let the user select part of the plot. Let's start with storage for the selection. We'll need two integer variables that can be accessed via read-only properties; therefore, add the following two properties to the class:

Q_PROPERTY(int selectionStart READ selectionStart
                              NOTIFY selectionChanged)
Q_PROPERTY(int selectionEnd   READ selectionEnd
                              NOTIFY selectionChanged)

Next, you need to create corresponding private fields (you can initialize them both to −1), getters, and signals.

The user can change the selection by dragging the mouse cursor over the plot. When the user presses the ...