The Mystery of playfieldpos

[+Gemintronic]

While trolling through the source files in this topic: http://www.atariage.com/forums/topic/148427-vertical-scrolling-through-a-playfield-that-wont-fit-the-screen/page__hl__defaultbasbin I noticed a command/variable/something called playfieldpos being used.

 

RT's command reference barely references it but it seems critical in the playfield scrolling examples I've seen in the linked topic.

 

Anyone have any clue what playfieldpos is and does? How it works?

[+batari]

It's an internal system variable that controls which line to start drawing the top playfield block and when to stop drawing the bottom one. The scrolling routines update it automatically so it's not necessary to use it unless you need to know where the playfield is located.