Resources for Retro style Games wanting 90 degree Window corners

I've been thinking of bringing some older games back to the modern Mac.

Rewriting old titles in Swift but using the original data files that assume use of non-rounded corners Windows.

Many of these games require all the Window space of a 90 degree cornered Window.

Can anyone point me at some useful workarounds or Is Apple simply deaf to the needs of this type of product?

This is just something I'm think of doing and I asm using Thexder, somethingI worked on a loooong time ago and am thus familiar with, as a away to learn Swift and Apples modern API's.

Resources for Retro style Games wanting 90 degree Window corners
 
 
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