Weird effects on Scuplted prims

I'm making a flower using two versions of sculpted prims (Large and Small petals). I then clone them twice each to create a lily. And strange thing happened. Even though neither the prims nor the texture maps consist of alpha they seem to suffer from the "transparency bug" ie, prims overlapping even when they have some distance apart. The viewer can't seem to determine which object supposed to be in the front or back. (see Pictures show correct and overlapped view.)

Is this a known issue? And is there anyway to get around it?

Thanks.

This has been a bit of a monologue but I think I figured out what the problem is. I saved the texture maps as PNG and even though there was no transparency the viewer seems to think is has. The overlapping problem went away when I save the maps as Targa 24bit. How weird.

yes this is a secondlife bug that the lindens dont seem to care about fixing .Somtimes an alpha channel gets added to png on upload when there isnt one . Uploading as a 24 bit tga normally works.

Thanks Eazel. I think that explains all those strange things happened to the objects I created for my shop. They overlap like crazy. I didn't realise that there was a PNG bug. I also noticed that 32bit TGA seems to suffer a lot less with the overlapping effect than PNG with transparency. I opted for PNG due to the ease of use since you don't need to create alpha channels. But looks like it should be avoided all together. I certainly will do from now on.

yes but make it a 24bit tga then it isnt possible for it to hold the alpha channel 32bit is just for when you have an alpha channel.

That's not really possible. First, as far as the renderer is concerned, transparency is transparency is transparency. When the texture is in view, it's just a collection of pixels, not a file. The format it's saved in for storage purposes won't affect its behavior upon viewing.

Second, even if the format somehow could make a difference, which again, it can't, it still wouldn't matter. All images in SL are saved in just one format, JPEG2000. As soon as you hit the Upload button, your source image is copied to JPEG2000, and then the copy is uploaded. The original never goes any further than your local hard drive. At that point, the source format becomes irrelevant. The deed is done, and the resulting JPEG2000 either has transparency or it doesn't. There's no special flavor of JPEG2000 that behaves differently if it happened to have been sourced from a TGA than from a PNG.

My guess is you probably just didn't replicate exactly the same conditions when you viewed the TGA-sourced textures in-world as when you viewed the PNG-sourced ones.



I'm not sure it can accurately be called a bug. At least in my experience, the problem can usually be attributed to user error.

Often when a PNG-sourced texture ends up with an unintended alpha channel in it, it's because there was some degree of transparency in the PNG which the user didn't notice. All it takes is for a single pixel to be less than 100% opaque, and the whole thing is considered to be "transparent". Or sometimes users mistakenly believe "PNG's don't use alpha channels", so they don't think to check whether or not their PNG's actually do have alphas in them before they upload them.

The latter is especially common with baked textures, since the default setting on a lot of renderers is to include an alpha channel with all renderings. Often, you have to go into the render settings before hand, and deliberately uncheck the alpha channel option before you bake. A lot of people may not realize that.

I would have to agree with Chosen. I use PNG images quite often and have never had a transparency related problem that wasn't my own error.

Pretty petals, Girlspeedo.

When part of the sculpted prim surface passes through another part, you get a "disappearance" of the part that is "herniated." For example, imagine that you take half of a cube and make it smaller than the other half and then translate the smaller half through the larger half. The smaller half will "disappear" and seem to be alpha in SL. Only the surfaces that have not crossed other surfaces are rendered in SL -- at least, that has been my experience.

I'm not sure what you mean, Poppet. Can you explain further?

I did this in sculptypaint:

make a cylinder, then select a portion of one of the flat ends and then translate that up through the other flat end.

Or you can make a prim and paste in this uuid

0a8fd5d5-e7cc-770d-6d9a-f6788039c856

That is the uuid of the sculpted prinm I made using that uuid

It is weird -- the inside face of the cylinder that is facing outwards is invisible, but you can see the texture that is on the outside of the cylinder as an inner surface, very hard to explain, here is a picture:

http://img136.imageshack.us/img136/1664/snapshot001mz5.th.png

Oh, that's what you meant. That's actually pretty easy to explain. When you tucked the part of the cylinder through itself, you turned that part inside out. Normals that ordinarily face outward are now facing inward. Turn on backface culling in your 3D modeling program, and you'll see the same thing happen there too.

Think of it like if you were in RL if to turn a sock inside out, and then stop half way through. The toe part would stick out through the the top of the sock, and where it does, you'd see the fuzzy inside material facing outward instead of inward. Only in the computer, the inner surface isn't fuzzy; it's invisible.

You see, Polygons in SL, and in most video games, are one-sided, meaning they're only visible from one direction, the "front face". When viewed from the opposite side, the "back face", they're invisible. This is why when you put a transparent texture on one side of cube, you end up seeing all the way through the cube instead of seeing the inside of it. The polygons would need to be double-sided in order for you to see the inside.

Ordinarily, you never notice the one-sidedness, since the outer surfaces of objects are generally all you're ever concerned with. But when you do weird things to geometry, like what you did to the sculpty in your picture, or when you twist a sphere all the way in both directions, you end up flipping the polygons over to expose the invisible inner surfaces.

I was just thinking that might explain what the OP was seeing as "alpha" in her flowers : )