Reproducing the surface behavior of a program, no matter how faithfully, is not in itself copyright violation if it's a cleanroom implementation. But int this case it's not to write the new one, the developers studied (and manually translated to C++) the original code, not just the program's behavior. So this is more of a case of a derived work, like a translation of a novel.
And Sony vs Bleem (or the IBM BIOS reimplementation) already set a precedent so that doesn't really matter anymore. Look at Wine. Or Exegutor. Or DOSBox.
All of them totally legal reimplementing either prior look and feel and functionality.
> The code of computer programs are excluded from design protection, but visual aspects of software are very commonly protectable as long as they are ‘new’ (i.e. not a direct copy of anything that has come before) and possess ‘individual character’ (i.e. that the design produces a different ‘overall impression’ than anything that has come before)
I'm no expect, but Chris Sawyer style games certainly provided a unique overall impression to me. Whether it needs to be a registered design or not I couldn't say, but it's not going to be cheap to find out.
More recent battles have relied on Trademark and Patent law rather than Copyright, but "Look and Feel" is still a legal grey area
Wine literally copies both the Win32 UI -needed to respect that for interop- , some of the kernel functions and Win32 which is just an API implementation and not copyrighteable per se. If not, we woudn't have GNU. Or Microsoft services for Unix.
You can retype someone’s book with your keyboard, it’s still not yours.