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Iowa Blaisdale

How do you add two ore more alpha channels over linked prims with Alpha channeled texture?

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There are many ways to avoid the alpha sorting problem, but they all take careful planning.  Basically, try not to put two alpha textures where they will interfere with each other.  Avoid using 32-bit textures unless you actually need the transparency, and then restrict them to places where they will have only 24-bit textures in most people's lines of sight.  If you have a 32-bit texture that someone else made -- say, a texture for a wall with a window in it -- you can make a "sandwich" by burying another thin prim inside the wall.  The extra prim blocks transparency where it's unwanted.

This is not only a SL problem, BTW. It's a feature of any graphical environments that use the OpenGL engine.  It's just more common here because most things in SL were built by amateurs who don't know how to avoid the sorting issue.

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Can there be a 24 bit transparency? I was trying to use two prims one inside the other both with 32 bit alpha channeled textures on each. It would blank out part of top image. It would also now blank out the inside texture if applied a alpha channel to a hole in the single prim. Avatars with alpha channel on feet, clothes and hair leave a empty hole when in the line of view of a window, transparent tinted floor or water. What you are saying, there is no solution? It is the nature of the beast? I must avoid doing things that way. If so, when ever any two Alpha channels cross in front of the other it will blank out?

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No. The alpha channel is the 8-bit channel in RGBA that makes a 24-bit image into a 32-bit one. The alpha sorting issue occurs because your graphics card's algorithms have no way to decide which one of the two alpha textures belongs "in front" of the other one. The best analogy I can think of in RL is the problem that we all have when we wash windows. It's very hard to tell whether a spot is on the inside of a window or the outside. The problem would vanish if the window was made of one-way glass -- transparent in one direction but not in the other one -- or if you used a window with a thin layer of something opaque in the middle (it wouldn't be a very good window, but you'd be able to clean it easily). Professional graphic designers know how to avoid these problems, and you can learn. As I said earlier, it's basically a matter of only using 32-bit textures when they are absolutely necessary and then thinking carefully about managing line of sight. Also, as I said, you can use 24-bit textured objects as screens to block the line of sight where necessary.

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What you are saying is I must use Alpha channel in one layer only and one side of prim must be 32 bit alpha channel and the other a 24 bit to prevent a hole if you have to pass in front. To have a 360 see though window I must put another tinted texture prim in the line of view?

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No. That won't work. Virtual reality is not the same as Reality. Surfaces in SL only have one side, so you only ever see a texture when you are looking at the "front" side of the face it's on. You can't see a 24-bit texture on the other side of a window prim unless you walk around to that side and try to look in. The alpha sorting problem isn't between the inside and the outside faces of your window. It's between the texture on the side you are looking at and other 32-bit textures beyond the window that are also facing toward you. What I'm saying is that if you have, say, a 32-bit tree outside your window, you'll have to adjust lines of sight so that people can't see the tree from inside the house. You can either move the tree or put a 24-bit wall in front of it.

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