READMEより抜粋
https://github.com/narzoul/DDrawCompat/blob/master/README.md

> DDrawCompat is a DirectDraw wrapper aimed at fixing compatibility and performance issues with games based on DirectX 7 and below on newer versions of Windows (Vista/7/8/10).
> Games using DirectX 8 and above for rendering are not affected as they don't use ddraw.dll.

なお適用されるのはDirectX7までを使用してるゲームで、8以降を使うものには効果がない。