As was mentioned above, Soldier of Fortune is already being ported, and John Romero did announce that Daikatana would be probably have a Linux client ported (a server port is a definite.)
Not sure, since I have never ported anything to Linux from Windows, but I do know that when Monolith released the Shogo Source code (or SDK, something along those lines), it was coded in pure MFC, which is not-portable. I would make the assumption that since they are porting the engine, it's mostly C++ and not MFC. Either way, they have probably had to rewrite quite a bit of it.
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As was mentioned above, Soldier of Fortune is already being ported, and John Romero did announce that Daikatana would be probably have a Linux client ported (a server port is a definite.)
Not sure, since I have never ported anything to Linux from Windows, but I do know that when Monolith released the Shogo Source code (or SDK, something along those lines), it was coded in pure MFC, which is not-portable. I would make the assumption that since they are porting the engine, it's mostly C++ and not MFC. Either way, they have probably had to rewrite quite a bit of it.