Celestia Forums

I have just joined the list, so apologies if this is a known issue -- I couldn't find it mentioned anywhere.

On my home PC (XP Home, SP2, P4 3.4GHz 3GByte RAM) with ATI1950 Pro (512Mbyte RAM), display card (latest drivers) I see artefacts on the rings of Saturn. I get rogue pixels corresponding to the edges between quads. This effect appears in all render paths (basic, multitexture, OpenGL Vertex Program and OpenGL 2.0).

See: http://myweb.tiscali.co.uk/blobchaser/CelestiaSaturn.jpg to see what I mean.

I have built a local version of Celestia and tried many things (control panel settings, disable blending and depth buffering, triangles rather than quads ...) to no avail.

Finally, I found something that removed the artefacts, but sadly it's not really a fix. If I disable mip-mapping (by setting the texture parameter to linear), the problem goes away, but of course, the rings then look aliased. I even tried generating my own mipmaps rather than using GLU, but the effect stays the same.

I am inclined to think that this isn't a Celestia bug, but a problem with my graphics card. Has anyone else seen this problem? Does anyone else have this card and do you see the same artefacts?

Cheers,

Steve.

That's strange . . . I do think that something is up with your driver. It looks like the texture address mode isn't being set correctly. Or, there's some problem with mipmap generation.

I do see one issue in the Celestia code that's making the problem worse than it should be: the ring texture is being repeated in each ring section. Ordinarily, that doesn't matter because the ring texture is effectively one dimensional. But, when there's a problem with the texture address mode, the 'seam' will show at the edges of each quad used for the ring geometry instead of just in a single place.

--Chris

Chris,

Many thanks for thinking about this. I'm not sure I quite understand your concern about the Celestia code. I tried various wrap modes which didn't make any difference, and I don't think its the mipmap generation either, as my own downsampler gave exactly the same results. I even tried converting the Saturn texture to a 1k x 1k image with no joy.

Anyhoo, I don't think Celestia is to blame. Time to investigate a new graphics card (36 shaders is looking a bit underpowered now!)

Cheers,

Steve.

I have had similar problems like this before and in my case it was my graphics driver. I use an ATI X800XL and found that older drivers work better.

Reiko wrote:I have had similar problems like this before and in my case it was my graphics driver. I use an ATI X800XL and found that older drivers work better.

Hi,

Thanks for sharing your experience. Maybe I'll try some older drivers to see what will happen.