A simple demo showing how to create a GUI with FMX to let the user draw two intersecting lines and then compute and show the angle between the two lines.
The use has to click on 3 points: the point where the lines intersect, the point where the first line (red) ends and the point where the second line (green) ends.
The user interface is updated in realtime following mouse movements.
Blog post at https://francois-piette.blogspot.com/2020/11/fmx-line-angle-demo.html