[Coco] Syscall to get the window screen and width

[Allen Huffman]

> On Mar 15, 2025, at 2:56 AM, Jeff Teunissen via Coco <coco at maltedmedia.com> wrote:
> 
> It is possible to gain direct access to the screen memory, but you have to
> give up some of your 64K to do it. That's an easy enough tradeoff for a
> game which might fit its code and the rest of its memory in 32K.

I wrote an article for OS-9 Underground showing how to map in the video screen to directly access it under stock OS-9, though the work on how to do that was provided by Robert Gault. Originally, I saw that NitrOS-9 added a system call for this, and was using it, then Robert showed me how I could make it run on stock systems (though, with a caveat — during the moment it acquires the screen, if the user hit CLEAR to switch screens it can break).

https://github.com/allenhuffman/SEGame

That simple demo showed how to do it in assembly, but the system calls should work in B09 and such I would think.

		— A