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Transparent textured prims vanishing over certain prims


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You have discovered the well-known alpha glitch, which is a feature of all virtual environments that use GL architecture, not just SL. It's an inescapable occlusion problem. Basically, your graphics card can't decide which of the two textures is closer to your viewpoint, so it tries displaying both of them, causing a flicker. The closest analogy I can draw in RL is to what happens when you are trying to wash a spot off a window and can't decide whether it's on the inside or the outside.  There are several ways to design around the alpha glitch -- the best one is to avoid using 32-bit textures unless you really need the transparency -- but sometimes it's impossible for even good designers to avoid it completely.  Hair is a good example.  The hair designer can't predict when you are going to walk in front of some 32-bit textured surface and create an alpha conflict, but she has no choice about whether to use alpha-textured prims in her hair.

ETA:  Yes, I know someone is going to point out that Linden vegetation doesn't cause this problem, but we mortal designers don't have the option of using their style of transparency. :smileytongue:

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For completeness, I should add that it's not simply a matter of whether the two textures overlap in your line of sight. The occurrence of an alpha sorting problem depends on the distance between the surfaces, the angle between them, and their angle to your line of sight as well.  Also, some graphics cards are better at resolving the issue than others, so two people viewing the same textures from the same spot may see different things.

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for two stationary objects this can be partially resolved by making sure that the prims in question have the exact same inworld position. which allows the calculations to us a fixed point for reference.....(note both prims must have visible layers, and it seems to work best if one is seen THROUGH the other)

as a bonus when you do this, other alpha textures that are between the camera and the viewer will also tend to sort better.

the effect is NOT guaranteed to work, but does tend to work over a wider range of situations than the norm

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  • 2 years later...

Hey there.  Quick question and I do realize this was 2 years ago you posted it...lol  I am just getting started really hunkering down into making my own textures.  In the past I have used PNG 24 file type.  I just now noticed that there is an option for transparency when you save for Web.  I'm trying to avoid the transparency all together by filling in window holes now.  Just wondering if PNG 24 is the best to use in SL as file types go.  I use Photoshop CS6 and PNG's used to be what I would use in transparent prims but before I got this new computer I never noticed what you are talking about above (probably a better graphics card).

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Exaurious Zemenis wrote:

Just wondering if PNG 24 is the best to use in SL as file types go.

You can't use PNG in SL, the internal format is jpg2000.

This means you can use any lossless format to keep the loss after upload to a minimum. You can use BMP, TGA or PNG for 24 bit textures and TGA and PNG for 32 bit textures. Stay away from JPG.

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