Celestia Forums

Friends,

For some time I have noticed that there is something wrong in the way that Celestia displays when I select the OpenGL 2.0 render path. It happens at both my desktop machines, at home and at work, both sporting GeForce FX 5200 cards, 128MB, with updated drivers. PC's are XP boxes, Pentim 4 3Ghz, 1 and 2 GB RAM.

The first effect I saw when choosing the OpenGL 2.0 path is that haze in atmospheres is not seen, as opposed to what happens when choosing the vertex/combiners path. Shadow borders, nevertheless, are correctly displayed smooth by OpenGL 2.0.

The most recent problems I have seen are the lack of the new atmospheric effects recently incorporated by Chris, which I tried with a fresh CVS distribution, compiled by myself. For example, when reproducing the sunset image shown by Chris, what I see under OpenGL 2.0 is almost identical to what I see under vertex/combiners.

Does anyone have a suggestion? Is there a setting that I could change, either in Celestia, or in the display properties? Thanks in advance.

Guillermo

This is the content of the OpenGL info box in Celestia:

#1
From what Chris has written (either here or in the developers' mailing list, I don't recall which) the original Haze effect is not going to be implemented in the Opengl 2.0 render path. An equivalent effect is being drawn due to the atmospheric dispersion effects now implemented, but it isn't as pronounced. Note the brightening of the limb when Show Atmosphere is enabled. You could try varying the Mie and Rayleigh parameters to see what differences they make.

I created this "Addon" SSC file to demonstrate the effect and make the images below:


Here's what I see with and without atmosphere enabled. There's clearly a haze effect.



(Sorry, no URLs: I couldn't take the time to fight with the space problems.)

#2
Did you remember to add the Mie and Rayleigh parameters as above?
(It does still need some more work. Stars are vislble while the sun is up, and the atmosphere doesn't always go all the way to the horizon.)

This is what I see in the OGL2 render path. The other render paths have a much redder horizon.



And here is a Cel: url to take you there:

sunset

(It works for me using Firefox under Windows)

[edit]
System:
1GB 3.4MHz P4-550, WinXP Pro SP2
128MB GF6600GT, ForceWare v84.21
Celestia built from CVS on Aug.10.

It should work with any of the 5nnn cards, too.
[/edit]

Many thanks, Selden. As always, your reply has gone directly to the point. I wasn't aware of the limitation of the OpenGL 2 path to render the "traditional" haze. I have used your suggested parameters for the atmosphere, and the display is as it should. There is nothing wrong with my cards.

Regards,

Guillermo

selden wrote:(It does still need some more work. Stars are vislble while the sun is up, and the atmosphere doesn't always go all the way to the horizon.)

This is not as unrealistic as one may think. It is possible to see a couple of the brightest stars during the day with the naked eye when the sun is up. It's a matter of knowing exactly where to look, like Venus. Sirius, for example, can be surprisingly easy to see during the day under the right conditions.

I think what's needed is some way of limiting the magnitude of stars. The limiting magnitude of the daytime sky is about six or seven magnitudes brighter than the nighttime sky. The sky is also much brighter, which makes the few stars that are visible during the day much harder to see.

The amount of stars visible during daylight is controllable by the height field in the atmosphere declaration in the ssc file. With the new OGL2 cvs code anyhow. These following screenshots all use MieScaleHeight 16. The first has height set to 30 km. Even though the sky is almost black almost no stars are visible.



The second uses 20 km for the height.



The third and fourth use 10 km height. Note that all the shots are about 15 km high from the earth except the last one is about 7 km. Notice all the stars that are visible even with a blue sky.





Anyhow the higher the atmosphere is in the ssc height field the less stars are visible.
I like to have it at 30.

cartrite