How to automatically calculate the area of ​​an arbitrary 2-D figure?

Question

Automation

Are there ready-made solutions for automated calculation of the area of ​​a figure specified by the user with his hand (mouse, touchpad, touchscreen, graph tablet)?
If so, which ones?

Answer 1

And how does the user enter this figure?
In general, any CAD system can calculate the area of ​​the drawn figures.
If you want something different, then here are the options:
If the figure is given by straight lines: https://ru.wikipedia.org/wiki/Gauss_area
formula is the amount per pixel area.
If the figure consists of more complex shapes - arcs, bezier curves, etc. - it's more difficult (here xs. You probably have to break it)