Transparency

[Wandering Soulstar]

Another question ...

Is there any way to deal with the 'issue' alpha channel conflicts (at least I think that is the problem). Basically I have a prim that I use for a lake .. and another prim that has a texture that contains some sort of  alpha/transparency seems to mess up the view  (i.e. the wtaer prim shows through the plants in this case .. any fixes for this?

[Peggy Paperdoll]

Aside from moving one or the other prim with the alpha channel to a position that it is not viewed inline or changing one of the prims that contain the an alpha channel to a prim with no alpha channel, there is no solution.  It's the nature of alpha channels and how graphics are rendered in a 3D invironment.  It can get complicated............but, those are your options.

[Jennifer Boyle]

Can someone refer me to something I can read to understand what the alpha channel is?

 

Thanks.

[Ceka Cianci]

here you go 

http://nicolaescher.com/tutorials/alpha-channel-primer

[Void Singer]

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Peggy Paperdoll wrote:

Aside from moving one or the other prim with the alpha channel to a position that it is not viewed inline or changing one of the prims that contain the an alpha channel to a prim with no alpha channel, there is no solution.  It's the nature of alpha channels and how graphics are rendered in a 3D invironment.  It can get complicated............but, those are your options.

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not necessarily true... you can sometimes fake it into giving you the correct sorting order in some scenarios....

I use one version of this to make low prim, high detail furniture. by centering a cube textured on the outside inside of a hollow cube textured on the inside you can get some very detailed structures that show through without sorting errors 95% of the time.

transparent textures with the same prim centers but rotated seems to work about 75% of the time, you can sometime fudge the sorting order by adding a transparent hollow, which takes it up to about 80% depending on the structure.

sculpt hacked objects often display similar characteristics, when the external texture is showing from opposing sides with no gap (like many sculpted plant/grass objects do)

the neat thing about objects built on these techniques is that they also tend to behave better with objects that are not

[Qie Niangao]

Also, they keep tinkering with the alpha masking heuristic in recent releases of Viewer 2.  This has more or less the same objective as the "Fast Alpha" option in V1-based viewers (IIRC somewhere under Debug or Advanced menu).  In V2, this works much better, and gets turned on by default for some graphics cards (because the deferred rendering version is on by default, and some super-high-end graphics cards get deferred rendering turned on automatically); the settings can be toggled under Advanced / Rendering.

Anyway, the point of alpha masking is to make tractable the alpha sorting problem by forcing any pixel of texture to be either opaque or transparent -- that is, one-bit alpha.  The trade-off is that there is no alpha blending at all: the front texture's non-alpha pixels fully obscure anything behind them.

Whether this option is turned on or not, Linden plants always use one-bit alpha masks... which is why their edges look so choppy -- they're dithered instead of alpha-blended.  But you don't get alpha-sorting problems with Linden plants.

[Jennifer Boyle]

Thanks so very much, Ceka.  That page explained it so well.

[Dresden Ceriano]

Hey Qie, maybe you know this... I remember reading somewhere that you can actually use 1 bit alphas in SL (it was somewhere in the forums but I can't recall where I read it). Something about saving a pgn a certain way in photoshop... I meant to test it out but I was taking a sabbatical from SL at the time. Do you know anything about that? Of course, even if you could, your point about blending would probably still hold true.

...Dres

[Qie Niangao]

I'm not a texture expert by any means, and I don't even use Photoshop, but I'm sure it has a way to threshold alpha as Gimp does, which would produce an image that looked the same as one that had a one-bit alpha mask (although, when you upload it, I think it will come with an alpha channel the full eight bits deep).  I think, however, that the viewer would still need to be set to do its own alpha-masking in order to get it to sort properly.

I vaguely recall discussions, I think in an old Nyx office hour, about getting the viewer to directly use user-supplied one-bit alpha masks, and I believe there was general agreement that this would be a good thing, but can't remember any specific plans about it.

[Void Singer]

there was a rumor that it had been quietly turned on... although as far as I can tell only PNG uploads would allow for it by default (and you'd have to encode them as single color value alpha) unless the alpha channel in a TGA was only all black and white values. I never did get around to testing that. I can't remember who mentioned it but it was a thread in the texturing forum.

[Dresden Ceriano]

Found it here... it was Penny and she said it works, I definitely need to try it now that I'm back inworld again.

...Dres