After reading the replies, I went back to my code and had a good look over, taking what you guys said. Turns out, I didn't follow proper rasterization rules which was causing all manner of problems in my code.
This bit from MSDN might help someone having the same problem:
"Non-antialiased line rendering rules are exactly the same as those for GDI lines."
@Alberth, Thanks for the extensive post. I made my decision and will continue on my current path of doign the engine in VS C++ and the editor in Delphi. I do have Rad Studio, so I can use C++ Builder in time to start the conversion.
@ryan20fun, I'm using the unmanaged version of Delphi, so AFAIK, pinvoke is out of the question. But hey, I know very little about it and I need to look into it. Thanks.
@WozNZ, huh, I havent heard about Oxygen in years! I'll take a peek and see where they're at. Thanks!
@SmkViper, I always tried to stay away from .NET and WPF, but it is so widely used that I should take a look at that since I have Vs. Thanks mate!
@alnite, My problem with Delphi/Rad Studio does not stem from the codebase in general, but rather the way Embarcadero is taking the product as well as the quality of the IDE itself. I have the IDE crash on me at least once a day. I end up chasing quirks deep in the VCL source, or rattling my brain trying to understand their Direct2D implementation since the docs are not that amazing. And frankly, as someone that has decades of programming experience but just trying to finish my first big game project, Pascal is not the way to go.
Please dont get me wrong. I love Delphi, but it will never match VS in term of power. I just watched a video on the new DirectX debugging features of VS2015 and I was blown away with how powerful it is and how deep you can investigate. Yet, interface-wise, nothing matches the speed at which you can pump out native Win32/64 apps.
Embarcadero isn't the same since Nick Hodges left...
And alnite, you're totally right, a game doesn't have to be written in C++. But I believe that using Delphi will make things more complicated. The first time around anyways!