Understanding Alpha Modes

Understanding Alpha Modes 

If you’ve ever had layers disappear on you, layers that are blacked out, lace that is mutilated or skin layers that disappear at some angles, it’s likely to be because of an improper alpha mode settings!
Luckily, most of these issues are solved with proper scripting, and with a little bit of knowledge, you can fix issues that have been missed by the creator’s eye!


Part One: Skin Layers & Alpha Mode: None
You may have heard the general wisdom that Skin textures should always be created using 24bit TGAs.
The reason for this is fairly simple…in SL 24bit TGAs default to Alpha Mode: None.

This is very important because skin layers should ALWAYS be set to Alpha Mode: None. Any other setting will create an array of frustrating glitches,

There is, however, a glitch with 32 Bit TGAs that makes the alpha mode of the skin change when the texture is applied.  Thankfully, there is a way to script against this glitch. (Mesh makers, you can find the fix for this glitch here)

If you’re using an Omega Skin Applier you should almost never run into this glitch.  All Omega Plug-ins and Listeners force the skin layers to Alpha Mode: None and we make sure the Mesh Makers we have Relays for, understand how to fix this glitch. However, if you see any of the following, you may still have an issue:

Symptoms of Having the Wrong Alpha Mode on your Skin Layer:
  • Disappearing Skin layer
  • Disappearing Clothing Layers
  • Glitched skin layer that you can see halos of itself through (see image to the left)

How to Fix:
This depends heavily on what body you’re using, and with no-mod bodies, you may be out of luck.

Tactic A: Convert the Skin appliers you have into Omega appliers and use them again.  Omega Skin appliers always force the Alpha Mode to None, fixing your issue. This, however, does not work with any mesh that uses a Relay. (Currently Sking, Maitreya, Jiggle Booty, ect)

Tactic B: If your body is mod, you can rez it on the ground and edit it.

  1. Rez the body on the ground.
  2. Rightclick –>
  3. Go to the texture tab.
  4. Use Select face to select the skin layer.
  5. Change the Alpha Mode to None as shown here.
  6. Repeat for every link and face of the skin. (There may be alot of these thanks to alpha-cut huds being so popular)
Tactic C: Open up a fresh copy of the body and try applying the skin again. If it still has the issue, contact the skin maker and ask them to redo your appliers with .tngs.

Part Two: Clothing Layers and Alpha Mode: Blending/Masking
 
Everyone seems to have an opinion on what is better for your clothing layers… Alpha Mode: Blending or Alpha Mode: Masking.
The long and the short of it is this:
Alpha Mode-Blending
Gives you lovely soft Edges as seen here with this lace dress top from Maai:
Alpha Mode-Masking
does this.  Every point on the texture is either “on” or “off”
eliminating all soft transitions from transparent to opaque.
But this isn’t the whole story.  With Alpha Mode-Masking, you have what is called a threshold. The image above is at the commonly used 150. If can, however, be changed, the image on the left is Threshold 0, the middle is 50, the image on the right is threashold 225. (notice how smaller numbers = more coverage?)

So why use alpha mode masking if it looks this terrible?

a) It doesn’t always look this terrible. Alpha Mode Maskings main issue is with sheer, lacy items. Solid items look much better, like the bottom of the same dress…the image on the left is alpha masking, the image on the right is alpha blending. Unlike the lace, there is only small decrease in appearance, especially when viewed at normal distances. (Ie.. your face not up in ssomeone’scrotch! xD)

 

b) You can’t have more then one layer set to Alpha Blending without having mesh glitches.

Saddly, all graphic cards/viewers/meshs/clothing/textures/ect have this issue. It’s not something anyone can work around. It’s a fundamental flaw in how graphic cards (all graphics cards) handle semi-transparent textures. This is why in video games you rarely see alpha blending. (Go ahead, peek around your favorite video games, you will find they just bake all the textures into one layer 99% of the time, and that when you look closely, those trees and shrubs that look so lush, have the telltale hard edges of Alpha Mode Masking.)

Symptoms of multiple Alpha Blending Layers:

  1. Layers flickering
  2. Layers disappearing or not showing up
  3. Layers appearing, but in the wrong stack  order. (ie, bras on top of tops!)

Basically, you need to plan your outfits so only one layer requires alpha blending. This can involve some tough choices… do you want the outermost (and most visible layer) to have it, or the underlying lacy layer?

So how do you Change your Clothing Layer Alpha Modes?

Again, this depends on your mesh…

Tactic A: Check the hud that comes with your mesh. Most recent mesh makers are building the options right in the hud.

Tactic B: If your body is modify, you can rez it on the ground and edit it.
  1. Rez the body on the ground.
  2. Rightclick –> Edit
  3. Go to the texture tab.
  4. Use Select face to select the clothing layer you want to change.
  5. Change the Alpha Mode to Blending or Masking as needed.
  6. If you’re changing the mode to alpha masking, remember to also set the “Mask cutoff” or “threshold” field. A recommended starting point is 150, but you should play with it to see what looks good to you.
  7. Repeat for every link and face of the layer. (There may be alot of these thanks to alpha-cut huds being so popular)
A tip for the adventurous: Nothing says every face of a clothing layer needs to be the same alpha mode and/or threshold. If you have something lacy on calf and on your thigh, and there are alpha cuts between the two, you can set textured parts of each layer to blending,  and set the rest to masking. The important thing is that no two overlapping faces can be alpha blending!

Update:

There seems to be some evidence, that wedging a layer with Masking Mode in between two blending layers will also drastically reduce.. if not eliminate alpha-glitches entirely.  Unfortunately, because of the nature of the problem, it is hard to test this definitively, but keep it in mind if you find yourself needing two layers to have blending.