Don't know if this has already been posted here, but it seems not, so:
Overflow released the source code to Logon's Run - a demo which ranked 2nd (but should have won!) at the Revision oldskool demo competition in 2017.
https://overflowlogonsystem.wixsite.com/amstradcpc/post/logon-s-run-source-available
I think this is a really great source of inspiration and learning for anyone interested in making demos on the CPC :)
The polygone routine may be usefull for many things ;D