Is there a noticable quality difference in the scenery when comparing D3D to Opengl rendering ?
When I played Myth in 1997, I had one of those Monster 3D cards by 3dfx that used opengl. I seem to remember that the landscape looked a lot smoother back then. Maybe it was the Landscape Filtering ? I don't even have the option to check that box with my Geforce card. Am I imagining this or does direct3D really give the game a rough look.
If there is a difference, what could I do to get Myth to look it's best ? Different graphics card ?
Direct3D vs Opengl
Myth didn't support OpenGL back it was released. It probably used 3dfx with your card, which was a proprietary protocol only supported by... 3dfx cards.
Landscape filtering checkbox is only for software mode (software mode rendering generally looks rougher than the video card based ones).
Generally, there should be no difference between D3D and OpenGL, though one or the other is better supported on different video cards (better FPS, or sometimes one of them just doesn't work on some cards). The only other noticeable difference is that text in D3D is blurrier, since anti-aliasing is done on it by default, whereas under OpenGL it's displayed as is.
A better video card would likely not give you a better graphics quality in Myth II, unless there's really something wrong with your current card's handling of Myth II.
Landscape filtering checkbox is only for software mode (software mode rendering generally looks rougher than the video card based ones).
Generally, there should be no difference between D3D and OpenGL, though one or the other is better supported on different video cards (better FPS, or sometimes one of them just doesn't work on some cards). The only other noticeable difference is that text in D3D is blurrier, since anti-aliasing is done on it by default, whereas under OpenGL it's displayed as is.
A better video card would likely not give you a better graphics quality in Myth II, unless there's really something wrong with your current card's handling of Myth II.