The Battle of the Alphas!!:

Hello SL citizens and Lindens,

There is a graphical anomaly I would like to address:

For some reason, the SL engine does not like to display an alpha channel that is being viewed through two other alpha channels. To be more specific (to my understanding), when a prim which has been textured with an alpha is being viewed at the same time through two other alpha channels, there is a battle of display between all the alphas.

The Battle of the Alphas!

I’m guessing this is MUCH harder to remedy than one can imagine—if it were a relatively simple matter, this would have been resolved long ago, because as I see it…it’s a major problem.

I strongly urge the Linden team to consider testing new code to solve this anomaly. I’ll give you one example why it’s important: If you have a building that has a lot of glass windows or walls, and inside, you have many objects that you want to lay shadows under. Let us say that a table in this building is also glass…well if I viewed the table shadow through both the outside window, and the glass table-top…the table shadow would shimmer and shutter. It’s actually kind of hard to describe, but I gather those that are “in the know” are the ones I’m addressing to begin with…so I don’t need to go any further.

Regardless, I love the SL engine. But please, take care of the battle of the alphas.

Thank you, and good day.

ps. I'm assuming this is not my particular graphics card, and is a SL engine anomaly.


~MB
Glowbox Designs & the V3 Group (Silverscreen)

Incorrect alpha z-sorting is a known bug, and is apparently a problem in many OpenGL implementations. I haven't really seen it outside of SL myself, but my guess is that other companies know about it and avoid it in their content design. SL doesn't really have that luxury, since all content is user-generated, so users have to do whatever they can to avoid it.

It IS a bug, though, and whoever is responsible for it should fix it, be it LL, your video card manufacturer, or the OpenGL consortium (if it is a design error in their specs).

Excellent answer Talarus.

I haven't seen it in other applications either, and I suppose--like you said--it is because designers are aware of this also. Well, it seems that in the past 10 years of game-engines (Doom to Bioshock) we would have figured out how to solve this problem...if it is indeed an OpenGl thing.

It really is too bad, because I find shadow implementation of upmost importance in sim creation...and when I am able to cast shadows believably in some areas, but not in others--due to OpenGl issues--it really gets my goat. Basically, it's a shame that I have to design and structure around such an anomaly. For example, a specific section of a sim might be fully shadow-cast, but a certain piece of that sim will obviously be missing shadows, because of alpha-fighting--this would be obvious to a designer or invested client.

Humbug! Humbug I tell you!

~MB
Glowbox Designs & V3 Group (Silverscreen)