|Second Life Alpha Masking and Sorting Illustration|
Alpha sort demo
This is supposed to look like two disks crossing each other. C is how it should look. A & B show how it actually looks in Second Life from two different angles.
I made the object using two flat, square prims with a filled circle texture applied to the front and back faces. The circle texture has an "alpha mask" which effectively hides the unwanted parts of the image.
Second Life renders the masked part of the image as transparent. Without the mask, the square corners would typically show as white. (D shows how the texture itself looks in Photoshop. The dotted line is the outline of the mask.)
What's happening in A & B is that Second Life can't decide which part of the object should be in front and which should be in back. So you get that weird flashing look where parts of the object normally in back will suddenly jump in front depending on your viewing angle. You'll see this problem in everything from prim trees to prim skirts and outfits. Even worse, try standing in a building with lots of windows. Sometimes it will look like objects that are physically OUTSIDE the building will look like they are inside and vice versa.
We need answers!
So why am I writing about this? Simple. Linden Lab has known about this issue since forever; they seem to have the ability to MOSTLY solve it; and yet, they haven't done so. A simple case in point is that Linden trees do NOT show the sorting problem YET Linden trees use alpha-masked textures. I won't bore you with all the technical details (frankly, I don't fully understand them myself), but I will point you to the JIRA issue that was created almost 3 years ago. I got involved in the issue because it affected my fashion designs and dammit, I wanted it fixed!
Three years and still NO Lindens assigned to work on it. Three years and numerous solutions offered by residents but no action. In fact, reading between the lines from some posts by Lindens participating in the JIRA discussion make it sound like one of their proposed fixes could be worse than the original problem.
So if you'd like your Second Life builds, outfits and general experience to be better, please view the JIRA issue above, log in and VOTE for it. You can also drop in a comment such as "Fix this now." Maybe then the Lindens will take it seriously.