Example of some Touchscreen GUI parts of radio interface using SDL on the raspberry pi (with 800x480 touchscreen).
Code in C++, classes and stuff, so rather new to me!!
This guy was really useful for general C++ coding basics and more, to me anyway: https://www.youtube.com/watch?v=18c3MTX0PK0&list=PLlrATfBNZ98dudnM48yfGUldqGD0S4FFb
This was based around the Langstone SDR interface.
Uses SDL2.0.12 - https://www.libsdl.org/download-2.0.php
The build script will help you compile it.
The frequency selector part works nice, touch the upper or lower half of the number to tune.
Buttons just click 'in' or 'out'.
Sliders slide as expected and change colour