Celestia Forums

Hi all,

I recently downloaded a Mars texture based on the Kim Stanley Robinson series "Red Mars, Blue Mars, Green Mars", and i've been playing around a bit, and thrown together a basic night texture map.

Celestia, so far, won't display my night texture, and after reading through some of the Add-on guide material that Selden wrote, i have come to the suspicion that the reason it will not display my Night Texture is that i do not have an appropriate "alpha channel".

This is the code i am using:



At first, the rgbmars map didn't work either, but i worked out that it was because i had Mars rendered as a .cmod mesh, so i added a # before my 'modify mesh' command, and voila, the rgbmars map worked perfectly. Unfortunately the night texture didn't appear.

So, i read through Selden's Creating and Using Surface Textures guide, and found that night texture maps require an "alpha channel". So i thought, "Maybe my night texture doesn't have one?"

Since then, i have been trying to figure out how to put one in (using Photoshop), and i just can't get it right.

My approach (based on what i could glean from the photoshop "help" files under "alpha channels") has been to make a greyscale image of the whole map, click on the "new channel" button on the bottom right-hand corner of the screen (under the "channels" tab), and paste the greyscale image onto that channel of the picture.

Unfortunately when i save it, and look at it in Celestia - no night texture. Then when i re-examine the file i thought i'd just added a new channel to, the only channels present are red, green, blue, and "RGB" - no trace of my Alpha channel.

Does anyone know what i might be doing wrong?

I can't help with your photoshop problem, but a night texture should work without an Alpha channel. The Alpha channel just lets the underlying surface texture be visible. I should make that clear in the documentation. Sorry.

Can you see the image if you use it for the primary surface texture? If not, then the problem is something else.

Liar wrote:Celestia, so far, won't display my night texture

I'm assuming night lights work for you on the default Celestia Earth? Did you try using the default Earth night light texture, or any regular texture without an alpha mask, for your Mars project? Just for verification?

Also, be sure you didn't inadvertantly disable night light rendering. You can check that by looking in the 'Render>View Options' dialog.

Since then, i have been trying to figure out how to put one in (using Photoshop), and i just can't get it right.

Don't feel too bad. Having learned graphics editing using Paint Shop Pro I've always found Photoshop unintuitive and frustrating when working with alpha masks (IMHO). But in this case, as Selden mentioned, you need not be concerned about using one in your night light texture.

Lone