Alpha bug fix by 1.9.2/1.9.3 - I can dig it

Philip Linden: OK... that alpha ordering bug...
Philip Linden: I have an update on that.
Philip Linden: We have a change that should fix that alpha prob in 1.9.2 or 1.9.3

I think this is one of those little fixes that's going to mean a lot to builders. Finally being able to layer alphas without the flicker is going to make for a lot more professional-looking builds and some truly cool effects.

Added bonus - target date of June for Mozilla. The grid's about to get a lot more interactive and hopefully less spastic to look at.

/happydance

/holdsbreath

/happy dances while holding breath, turns blue, passes out.

*dead*

I will believe it when I see it. Or in the alpha ordering instance...when I don't see it. (ie) Property Lines overlapping my objects.

This is good news and bad news. Fixing it will solve many problems, sure, but it will also create a whole host of new ones. Without the alpha sorting glitch, just about every tree in the world will break (including Linden trees), as will prim-based fire, shrubbery, certain chandeliers, candelabras, and lots of other objects that are built specifically to take advantage of the glitch.

So, careful what you call good news. I'm reserving judgment until there are more details on exactly how they're planning on "fixing" it, and what options we'll have for alpha sort display. If they impliment something similar to what Maya does, where the glitch can be turned on an off on a per object basis, that would be something. Maya's the only program I've ever seen that can do that though, so I'd be suprised if SL will. My feeling is we're in for trouble here, but like I said, I'll reserve final judgment until we have more info.

Whoah, do you have something in your inventory that uses the glitch that you could pass me as an example? I never thought that the glitch was something you could utilize to achieve a certain effect - I always thought it was too jumpy and sketchy to rely on.

Yea, i would like to see this better explained aswell.

Me too, me too, MEEEEE TOOOOOOOOOOO

*does the happy dance and dies anyways*

Explaination?.....
Answer: uh...

That about sums it up right there.

I can't believe that anybody believes this will really happen just because Philip rattled a few keys at a townhall.


Please

Sorry if I wasn't clear. I thought this common knowledge. Guess I hang out in the building and texturing forums too much, and not enough in General. I'll explain.

First, maybe some background might be in order to put this in perspective. The alpha sorting glitch is not just an SL thing. It is an OpenGL issue that is common to nearly all 3D applications, including just about every video game on the market and even high end 3D modeling packages. Because it's so prevalent, modelers both in and out of SL have learned to take advantage of it to construct certain types of objects, trees and other vegetation being the most common.

Here's what happens. The glitch is not "jumpy and sketchy", but actually quite predictable. The surface that is most facing the camera always gets the drawing priority. Surfaces facing more away from the camera end up getting drawn "behind" the one that is most "facing front".

So how can objects be built to take advantage of this? Well, for a simple example, take a look at the trees and plants in your inventory library. Rez a few of them and move the camera around them. As you rotate the camera around each plant, it always appears to face the camera, which gives it an illusion of 3-dimensionality. Examine each plant carefully carefully though, and you'll see that they are not actually 3-dimensional at all. They are simply made of intersecting planes with alpha textures on them. They're more like paintings of plants than sculptures of them.

The reason they appear to face the camera all the time is because as the camera moves, and its orientation to the planes changes, the different planes take turns being "in front". Whichever plane happens to be most facing the camera at any given moment gets priority and the others "fall behind". Because each plane has the same plant picture on it, you get the illusion that you're always looking at a 3-dimensional plant (at least until you scrutinize). In this way, seemingly complex objects would take lots and lots of polygons to scult 3-dimensionally can be reduced to just 2 or 3 planes and a bit of clever texturing.

This is how all the objects I mentioned before are built. For another example, if you've got Eric Linden's flame object (I think most people do), rez it and take a good look. It's just two intersecting planes with an animated alpha flame texture on them, same construction as the trees and plants.

(As I said earlier, this technique is not just used in SL, by the way. World of Warcraft players, take a look at the trees and bushes in WOW. Many of them use this same type of intersecting plane construction. The same is true in lots of games.)

Were the glitch to be "fixed" all of these trees, flames, and other objects would cease to function properly. No longer would they appear to be anything more than what they are, a collection of boring intersecting planes which look nothing like the objects they are meant to represent. Granted, some of them don't look spectacular to begin with, but they do the job. Fix the glitch, and they no longer will.

If LL's got some magic up their sleeve to deliver somehow the best of both worlds n this issue, than I'm all ears to hear it. However, with the soul exception of Maya, which is advanced enough to toggle the glitch on and off to allow people to model for environments that might or might not have the glitch, I've never seen or heard of a program that is able to manage it well. In all other programs, it's either on or it's off, and either way there are lots of problems.

These pictures (the last of which made Best of Snapzilla) were made possible using our "friendly foe," the alpha-sort bug. While it can be a pain in many respects, I do hope it's not eliminated completely. I'm with the folks who'd like to see oldstyle-alpha vs. newstyle-alpha applied on a per-object basis, if at all possible without significant performance impact.

There's some kinda love/hate relationship going on with this bug, doncha think?

Historicly LL's position on this bug has been that, "yes we could fix it but most peoples hardware couldn't support it".

I hate to be a doubting Thomas here but - Why is it then, given what some members have described above about this bug, that I have a wall with textured windows in it, yet a plant with its prims set on an angle behind that wall displays as being in front of the wall?

The wall texture is the one mostly facing me, perpendicular to my avie's line of sight...

At any rate, you'd think they would be able to somehow prioritize it like draw distance, so that the glitch might be at least partially preserved for fire and plants? Not sure if that's possible.

In any event, I'm long past tired of neighbor's grass showing through my walls, and I know that each clump can't be angled perfectly so that it orders display in front of my walls... Unless my neighbor was that devious, and I am going to guess "no" on that...

There's a second effect coming into play here, "sprites" or "facers", (depending on where you are from).

Facers are used in the particle system and are simply a way of placing a texture at a "point" in space, not on a plane. From whatever angle you look at a texture defined as "facer" it is always perpendicular to you, so as you move around it, it appears to turn with you. It is also commonly used for plant, tree and grass textures.

Grass in SL makes use of facers, thus if you think you're standing perfectly square on to a wall, the grass behind it will always be mathematically perfectly perpendicular and hence be at the top of the alpha sort order.

The tree and window example was what I was thinking about, too. If you can get two alpha textures *just* far away enough from each other, they wont jump unless you're at an extreme viewing angle. The closer they are, the less extreme the viewing angle has to be before it jumps. That's what I meant by being spastic - you can kind of compensate for it, but it takes some thought in layout.

Also, say you make a texture with a wall and windows in it, the windows being semitransparent, but because its all one texture, the whole thing is technically alpha, even the completely opaque parts. You can see people's floating names through the opaque section of that wall.

Ah-hah!

Thanks!

Will be interesting to see what gets fixed and what gets broken.

Why does there always have to be a trade-off?

For the time being I'm giving Philip the benefit of the doubt, and waiting to see if it really does appear in 1.9.2 or 1.9.3.

However...I'm also half-tempted to think that means 1.9.2 or 1.9.3 might be a long long long ways away.


- Newfie

The last time Philip town halled i asked about alphas flashing out of order when they were texturing surfaces on prims that were very clearly placed in a specific order e.g. a potted flower sitting on a table 0.3 meters in front of a windowed wall.

He told me to email him the question.

I did.

He replied that he was sure that was fixed already and asked me to test it in the 1.7 preview.

I did.

It wasn't fixed so I took pictures and replied them to him.

...