Stopping prims flickering thru other prims when you move away?

This is probably the most common question in these forums, asked on average once a week it seems. You have rediscovered the alpha sorting problem that affects any environment based on OpenGL architecture. In simplest terms, when your graphics card has to deal with overlapping textures it follows a straightforward algorithm to determine which one is "in front" of the other one, and therefore which one occludes the other. When one texture is transparent and the other is opaque, the answer is trivial. When BOTH are transparent, the answer is impossible to determine. (In fact, in RL your own eyes would usually have a hard time figuring out which one of two sheets of glass is in front of the other one.)

Unfortunately, the problem extends to cases where both textures contain 32-bit pixels, even if the 8 bits that carry potential information about transparency aren't actually transparent. If two 32-bit textures are close together and overlapping, the system simply can't decide which one to display, so it flickers back and forth between them, depending on your viewing angle.

There is no cure. Avoid using 32-bit textures unless you really need them (they require 33% more memory than 24-bit textures anyway). If you need 32-bit textures for transparency, avoid overlapping them in close proximity.

Can I change a setting to improve the accuracy of rendering thin items close together as you move away?


Thanks

I responded to this question just a couple of days ago /8/97/304294/1.html. Rather than retype things, let me just paste the text in here again.....



For more information about alpha channels and transparency, read the sticky at the top of the Texture Tips forum. Good luck!

Right, Ceera. That IS a good possibility. Thanks.

It's also worth mentioning that if alpha sorting were the problem (and it still might be, so the OP really ought to check the textures on the floor AND the carpet to see), you couldn't assume that you could avoid it by using PNG textures instead of TGA ones. It isn't the presence of an alpha channel that makes the difference, it's the fact that the images are 32-bit rather than 24-bit. When you save a TGA file with an alpha channel, it is automatically 32-bit. You can also save a PNG file as 32-bit, however -- sometimes without meaning to.

I had this precise problem with the floor of the Rutgers Student Center, in the "Ruce 4" sim.

On the patio was a concrete texture. Inside the store was a wood floor texture, and the entry way is carpeted. All three textures are 24 bit, I am certain.

The only way to get the three textures so they never flickered was to reshape the floor prims so they didn't overlap at all, and so the tops of the prims could have the appropriate textures on them. The entry is one prim, topped wih carpet. The courtyard is several prims, topped wih concrete. And the odd-shaped floor inside is several prims, topped with wood floor texture. At no point to any of them overlap, though I could have saved many prims if the carpet in the entry could have overlapped the wood and stone floor sections.

With something like the TV example, you simply have to move it further from the wall.

Just like a prim with a round edge will roughen when you move a few meters away, so also do all prims. The farther away you get the level of detail is reduced so that your computer can display things in the distance. If everything stayed the same detail it would bog down your computer. The only way to fix the problem is to make flickering faces of the prims a few thenths farther from each other, either by making one thicker or moving it farther away.