Fast Alpha

Can anyone explain reasonably simply for me what this setting actually means.

At the moment when i see 3d builds with alpha textures on 2 sides of the same prim, that prim appears lighter compared to the rest of the build. (1.23.4 viewer). I didnt have this problem on the 1.22. viewer.

Now when i have the fast alpha setting checked this problem disappears, but I would say not quite as crisp when viewed close up, from normal distance looks good. Can anyone explain this for me please,

IT shouldn't really do anything anymore. Half the advanced rendering options are actually broken, with menu options just left in due to neglect.

Dante, it really makes a difference on mine you can see a vast difference. btw I am using Emerald viewer, whether that makes a difference? I will try it on the sl viewer.

Just tried the sl viewer and had fast alpha off turned it on and yes it makes a vast difference on that viewer too, so Dante this is working.

Yes, fast alpha does still work, as long as the deferred rendering pipeline isn't turned on. When enabled, it tells the viewer to cheat a little on more distant alpha textures, and render them as fully solid or transparent and skip all the sorting stuff that can slow things down.

Some early examples of the effects here (from before it was turned into a setting):

https://jira.secondlife.com/browse/VWR-3101
https://jira.secondlife.com/browse/VWR-4337

Also on Emerald- where is this Fast Alpha located?

It's the same as in the regular viewer, under Advanced->Rendering

Thanks- I will look- can't say as I had ever noticed it in any viewer!

To my PoV, Fast Alpha helps considerably with the alpha sorting problem at the expense of bright fringing on the edges of some alpha textures. I've not tested whether it improves fps.

Generally speaking, windows and the like where the edges are hidden are noticeably improved. Trees, flowers and some hair can look a bit messy.

Just tried a quuick test at Straylight, and fast alpha improves my fps marginally - but only around a couple of percent.

Pictures for comparison...

Fast Alpha off. Not obvious in this shot, but the dark green foliage top-left is closer than the lighter green willow. Alpha sorting strikes again.





Fast Alpha on. You can see halo'd edges on the darker trees.

The linden trees all have this behavior, i can't remember but it's basically treating 100% alpha as "nonexistant" and only do sorting work on the non 100% alpha.

big boost for peoples that have a lot of attachments with "invisible options" too.

Yep, that's how the trees are done, the new avatar transparency thing works like that too.

There is a JIRA requesting that this be made into a texture property that could be applied to prims: http://jira.secondlife.com/browse/VWR-6713 - it's on LL's roadmap, but there is no estimate on when it will happen.

Yes when I put the fast alpha on the trees can at a distance look a little like your pics. It was suggested to me in a group chat on another subject to try putting the fast alpha on to stop me seeing what I reported on the jira at this link

https://jira.secondlife.com/browse/VWR-4337

It does work and the builds look like the viewer 1.22 before.

Kelli how come you can attach pics to the forums it wont allow me to do so.??!!

The halo can be avoided when the texture is created by making the alpha background the same color as the edge even where it's "hidden".

Click the quote button on her post and you will see.

Great, so only lousy alpha texture makers get affected?

I vote for it, lol.

define lousy?

in that scenario, the edges may some some indeterminate color as the best background to match to when using antialiased edges... that's SOP for environment centric alpha textures. only cohesive models generally use the blend to edge color. no absolutes there (although I have to agree that most people don't properly pick their backgrounds and use a bad solid color when they shouldn't)

The magic of [IMG]tags

When I post other links, I'm never sure if other people see them as such, because I use a Firefox add-on that converts all link-text to clickable links.

With out touching the 'lousy' comment below, would you expand on alpha color? I thought alpha was- well - clear-

Alpha is a separate channel from red, green, and blue. So if a color is (255,0,0,127) that's "red, half-transparent".

Lets say you take an image of a green tree in front of a blue background. You generate an alpha mask based on blue, say by se1ecting a blue pixel and using a "se1ect similar" operation, or by "filling" the blue background with "alpha", or by doing some kind of smart se1ection of the blue and "cutting" it.

So areas near the edge of the tree that were originally (30,240,20 might end up (30,240,208,127) "half alpha" and "green-blue".

With fast alpha, or "1 bit alpha", anything that's got an alpha less than 128 might be treated as transparent, and anything more than 128 as fully opaque. That's how it gets around the alpha blending problem.

So if you have one pixel that's (20,240,208,127) and the next pixel is (30,240,192,12, only the second pixel will be seen. But it will still have a higher blue content than you'd expect from a tree, so you'd see a bluish or whitish halo around the tree.

One thing you can do to fix this is to generate the alpha layer, then go back to the original image and flood the background with colors that are close to the colors of the matching parts of the tree, then apply the alpha layer to that. It's tricky, and usually requires some manual work, and a lot of people don't know about it.

Thanks! Ferrets are such helpful critters Will try that out.

You can't, but it doesn't matter, IMG tags aren't attachments, they're links.

As a tangent here, one reason for the common white halo is that certain programs (I'm looking at you, GIMP) assumes a white background when flattening and exporting images, even when you think you're working with a transparent background in the layered file.

That's the problem when peoples want to make transparent tgas and don't even know what a color channel is.

that's why we say rgb colors it means

-one red channek
-one green channel
-one blue channel

and in the case of RGBA we have on top of it one Alpha channel

wich in SL's case (and many apps) govern the tranqparency of the image

but other formats than tga can have many more channels, like for specularity, bump mapping, etc...

(for example the raw format used by Linden labs for terrains has 13 channels)