CMOD Texture size limitation?

[selden]

It seems that CMOD models used for solar system objects can't display surface texture files that are larger than the texture buffer of the user's graphics card.

A Celestia user reported to me in a PM that he couldn't display any surface texture on Phobos larger than 1K, the size of his texture buffer. Phobos was drawn white, instead.

My card has a 4K texture buffer. I tried displaying an 8K JPEG surface texture image (of Europa) on Phobos. I put it in the hires folder and typed an "R". Eventually I saw Europa's cream-colored surface, but it lasted only very briefly, and then Phobos turned white.

Unfortunately, an 8K jpeg results in a 96-128MB decompressed image. Since my graphics card has 128MB, I can't be sure if the symptoms that I saw were due to running out of memory or if it really is somehow limited to how CMOD textures are being loaded when the texture buffer is smaller than the image width.

I think it might be helpful if someone with a relatively small texture buffer but lots of graphics memory could perform a similar test.

These tests were done with Celestia 1.3.2 pre8 and the current CVS version.

[Bob Hegwood]

Selden,

I have nothing to hide... The PM was from me. I just didn't know if this was
a bug, or something that I was simply un-aware of at the moment. To make a
long story short, I simply tried to apply Jens Meyer's 2k Deimos and Phobos
textures to the CMOD's used in Celestia 1.3.2 Pre8, and I saw the dreaded
plain white textures appear. This did *not* happen when I applied these same 2k
textures to 3ds models of Deimos and Phobos, so I just thought I'd ask around a
bit before logging in a bug. As you know, my system has only a 1k graphics buffer,
and I *can* display 2k textures for the normal, planetary, non-CMOD objects in
the Solar System.

No big deal though... I'll simply continue to use the 1k Jens textures I'm already using.

Thanks a lot, Bob

[chris]

CMOD and 3DS models both have the same texture size limitation. Only ellipsoids can take textures larger than the maximum size supported by hardware. Larger textures must be broken into tiles, and the splitting of meshes into parts that are each covered by no more than a single tiles is a challenging problem to solve generally. It's not something I plan to work on, as it would require a lot of time to solve the problem robustly and I think there are much more important things to be done. What I may do instead is to introduce new types of 'special' geometry that can have large textures mapped onto them. Rectangles would be useful and simple to implement, and so would some sort of displacement mapped spheres.

--Chris

[Bob Hegwood]

CMOD and 3DS models both have the same texture size limitation. Only ellipsoids can take textures larger than the maximum size supported by hardware.

Well, I could be wrong Chris, but I'm almost positive that I got the 2k textures to
work for Phobos and Deimos before. At any rate, no big deal. The 1k textures
look a lot more detailed on the CMODs anyway, so I'm hardly going to complain
about it.

Thanks for all your efforts with this "Celestia" thing... Truly an amazing piece
of work. Besides, if I could just jam a crow-bar in my wallet and spring for a
graphics card and some more memory, then all this would be moot.

Take care, Bob