water/cloud transparency problem

[alexfung]

I run Thief 2, which is a DX7 game. I found that the sky is very ugly, and other gamers do not see such an ugly moon.

To see the sky for yourself, look at four screen captures. They are made by standing at the same location (in mission 2) and turning the head around.

http://www.cfm-resources.com/a/alexfung/test/dump000.jpg

http://www.cfm-resources.com/a/alexfung/test/dump001.jpg

http://www.cfm-resources.com/a/alexfung/test/dump002.jpg

http://www.cfm-resources.com/a/alexfung/test/dump003.jpg

Look at how the sky looks with a TNT2:

http://www.cfm-resources.com/a/alexfung/test/good002.jpg

Look at the stars! At first I thought it was a fog issue. But it seems not. Theif 2 has a "sky details"
setting. If set to low, I can see the stars as well:

http://www.cfm-resources.com/a/alexfung/test/low007.jpg

but the sky is very ugly (like a child painting). Studying my original screen again and I noticed that
the sky is actually a cloud cover, which is moving (noticeable when inside the game). Therefore I think
it is a opacity issue. I think Thief 2 added the cloud cover only for some cards (like my GeForce) at
high details setting. However, it should be translucent (who want to draw all the stars and hide them
behind opaque clouds?).

Similarly, I find that the water surface is not transparent enough. I have to dive my head under water
to see clearly. Looks like the alpha blending parameters are not right.

I think there is a similar problem with 3dfx card with water opacity (ie the water surface looks completely
opaque instead of semi transparent). In glide, opacity can be manually set. Can similar things be done
with D3D?