Second Life Forums Archive - Partially Invisible Prims

Phil Moore

Sweet Piece

Join date: 30 Apr 2006

Posts: 32

06-18-2006 19:43

Every once in a while I'll get a prim (or a pair, in this case) where I can see through the facing surface and into the prim. If i'm looking at the front of the prim from a high angle, the front and top faces of the prim can't be seen, but the "inside" of the rear, bottom and side faces are shown.

Changing the camera angle just gives the equivalent effect, whatever side the prim is viewed from.

I need the prims in question to intersect with the prims below them, but it looks terrible when you can see the intersecting edges inside the "cap" prim.

And yes, before you ask, transparency is set to zero. I've tried texture, reflectivity and material variations, to no effect.

Has anyone else encountered this? Any suggestions for a work-around, or correction?

Thanks.

hurly Burleigh

Registered User

Join date: 19 Sep 2005

Posts: 167

its ok you are not going mad.lol

06-19-2006 04:02

I have had similar problems since the latest release. i had a set of curtains witn an alpha textures set of bars infront on a seperate prim. the prims were not on the safe coordinates but if viewed from an angle the textured seemed to get mixed up and i got half curtain half bars. i am not sure if this bug has benn reported yet

IceManiac Shatner

Registered User

Join date: 23 Sep 2005

Posts: 9

06-19-2006 05:42

Phil,

Often people make the mistake of uploading nontransparent textures as 32 bit TGA files, because they think that it's higher quality, while in fact the extra bits just store an alpha channel, if you have mod rights on the textures, try opening them in a graphics editor and saving them as 24 bit TGA files .. then upload them and try using those textures instead.

Hope it helps.....

Duke Scarborough

Degenerate Gambler

Join date: 30 Apr 2006

Posts: 158

Alpha textures

06-19-2006 06:12

The problem with alpha textures over alpha textures is well known.

There is nothing that can be done about it due to the way the rendering engine must work to stay near-realtime.

Chosen Few

Alpha Channel Slave

Join date: 16 Jan 2004

Posts: 7,496

06-19-2006 11:48

It sounds like Phil is talking about a problem other than the typical alpha sorting glitch, but since that's been mentioned, let me take a moment to address it. Here's an explanation of what it is from the Transparency Guide, stickied at the top of the texturing forum:

From: someone

Why do sections of images sometimes disappear or seem to change position in SL?

This phenomenon has to do with a glitch common to nearly all 3D applications in what’s known as alpha sorting. It happens in nearly all video games, and even in high end 3D modeling packages costing thousands of dollars. What happens is when two or more 32-bit images are placed so that they intersect or overlap in close proximity, the renderer has trouble determining which one to draw first. As a result, the images can appear to flip-flop their positions in 3D space, to cancel each other out, or to otherwise behave strangely.

The way to cut down on this is to make sure that 32-bit images are only used when absolutely necessary. Images that do not need transparency should always be saved as 24-bit. Beyond that, there are certain building techniques in SL that can minimize the effect, and others that actually take advantage of it, but building is beyond the scope of this guide. There are plenty of tips about this on the building forum.

Alpha sorting has to do with how multiple surfaces with alpha textures overlap eachother, which unless I'm reading something wrong, doesn't sound like what Phil's talking about at all. If I'm reading Phil's description right, he's not talking about multiple prims overlapping, but about seeing the inside surfaces of individual prims. If that's the case, the problem is reversed normals, and that to my knowledge would indeed be a brand new bug. At least, I've never seen or heard of that happening in SL.

To explain what "reversed normals" means, in 3D graphics lingo "normals" are the direction in which light reflects off a surface. For prims in SL, the normals are supposed to point outward, so that the prims are visible as solid objects from the outside. That's why when you put a transparent texture on the front of a cube, you can't see the inside of the back of the cube behind it. No light reflects off the inside surfaces, so the insides are always invisible.

Now, were the normals to be reversed on a prim, they would point inward. The reslult would be that the outside surfaces would invisible, and the insides would visible. As you rotate the camera around such a prim, you'd see that the outside surfaces keep disappearing as they turn to face you while the inside surfaces keep appearing. That sounds exactly like what Phil is talking about.

Phil, I would suggest you bug report this. If you can discover any repeatable circumstances that cause this to happen, LL will want to know about it for sure. Even if it's random though, report it anyway. Also, make sure your graphics drivers are up to date. It's possible the problem is just on your end.

_____________________

.

Land now available for rent in Indigo. Low rates. Quiet, low-lag mainland sim with good neighbors. IM me in-world if you're interested.

Phil Moore

Sweet Piece

Join date: 30 Apr 2006

Posts: 32

Hmm . . .

06-19-2006 20:05

Yeah, as far as I know, there is no alpha channel. I can see how that could produce a similar effect to what I described.

The prims should be showing zero transparency. The texture on all sides is set to blank with medium reflectivity. Straigh up Linden stock on the texture. Although several variations on texture and settings haven't changed the weird appearance.

I guess all I can do is bug report and put the build on hold for the time being. Aargh.

Thanks all for your input.

Partially Invisible Prims
Phil Moore Sweet Piece Join date: 30 Apr 2006 Posts: 32	06-18-2006 19:43 Every once in a while I'll get a prim (or a pair, in this case) where I can see through the facing surface and into the prim. If i'm looking at the front of the prim from a high angle, the front and top faces of the prim can't be seen, but the "inside" of the rear, bottom and side faces are shown. Changing the camera angle just gives the equivalent effect, whatever side the prim is viewed from. I need the prims in question to intersect with the prims below them, but it looks terrible when you can see the intersecting edges inside the "cap" prim. And yes, before you ask, transparency is set to zero. I've tried texture, reflectivity and material variations, to no effect. Has anyone else encountered this? Any suggestions for a work-around, or correction? Thanks.
hurly Burleigh Registered User Join date: 19 Sep 2005 Posts: 167	its ok you are not going mad.lol 06-19-2006 04:02 I have had similar problems since the latest release. i had a set of curtains witn an alpha textures set of bars infront on a seperate prim. the prims were not on the safe coordinates but if viewed from an angle the textured seemed to get mixed up and i got half curtain half bars. i am not sure if this bug has benn reported yet
IceManiac Shatner Registered User Join date: 23 Sep 2005 Posts: 9	06-19-2006 05:42 Phil, Often people make the mistake of uploading nontransparent textures as 32 bit TGA files, because they think that it's higher quality, while in fact the extra bits just store an alpha channel, if you have mod rights on the textures, try opening them in a graphics editor and saving them as 24 bit TGA files .. then upload them and try using those textures instead. Hope it helps.....
Duke Scarborough Degenerate Gambler Join date: 30 Apr 2006 Posts: 158	Alpha textures 06-19-2006 06:12 The problem with alpha textures over alpha textures is well known. There is nothing that can be done about it due to the way the rendering engine must work to stay near-realtime.
Chosen Few Alpha Channel Slave Join date: 16 Jan 2004 Posts: 7,496	06-19-2006 11:48 It sounds like Phil is talking about a problem other than the typical alpha sorting glitch, but since that's been mentioned, let me take a moment to address it. Here's an explanation of what it is from the Transparency Guide, stickied at the top of the texturing forum: From: someone Why do sections of images sometimes disappear or seem to change position in SL? This phenomenon has to do with a glitch common to nearly all 3D applications in what’s known as alpha sorting. It happens in nearly all video games, and even in high end 3D modeling packages costing thousands of dollars. What happens is when two or more 32-bit images are placed so that they intersect or overlap in close proximity, the renderer has trouble determining which one to draw first. As a result, the images can appear to flip-flop their positions in 3D space, to cancel each other out, or to otherwise behave strangely. The way to cut down on this is to make sure that 32-bit images are only used when absolutely necessary. Images that do not need transparency should always be saved as 24-bit. Beyond that, there are certain building techniques in SL that can minimize the effect, and others that actually take advantage of it, but building is beyond the scope of this guide. There are plenty of tips about this on the building forum. Alpha sorting has to do with how multiple surfaces with alpha textures overlap eachother, which unless I'm reading something wrong, doesn't sound like what Phil's talking about at all. If I'm reading Phil's description right, he's not talking about multiple prims overlapping, but about seeing the inside surfaces of individual prims. If that's the case, the problem is reversed normals, and that to my knowledge would indeed be a brand new bug. At least, I've never seen or heard of that happening in SL. To explain what "reversed normals" means, in 3D graphics lingo "normals" are the direction in which light reflects off a surface. For prims in SL, the normals are supposed to point outward, so that the prims are visible as solid objects from the outside. That's why when you put a transparent texture on the front of a cube, you can't see the inside of the back of the cube behind it. No light reflects off the inside surfaces, so the insides are always invisible. Now, were the normals to be reversed on a prim, they would point inward. The reslult would be that the outside surfaces would invisible, and the insides would visible. As you rotate the camera around such a prim, you'd see that the outside surfaces keep disappearing as they turn to face you while the inside surfaces keep appearing. That sounds exactly like what Phil is talking about. Phil, I would suggest you bug report this. If you can discover any repeatable circumstances that cause this to happen, LL will want to know about it for sure. Even if it's random though, report it anyway. Also, make sure your graphics drivers are up to date. It's possible the problem is just on your end. _____________________ . Land now available for rent in Indigo. Low rates. Quiet, low-lag mainland sim with good neighbors. IM me in-world if you're interested.
Phil Moore Sweet Piece Join date: 30 Apr 2006 Posts: 32	Hmm . . . 06-19-2006 20:05 Yeah, as far as I know, there is no alpha channel. I can see how that could produce a similar effect to what I described. The prims should be showing zero transparency. The texture on all sides is set to blank with medium reflectivity. Straigh up Linden stock on the texture. Although several variations on texture and settings haven't changed the weird appearance. I guess all I can do is bug report and put the build on hold for the time being. Aargh. Thanks all for your input.

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Partially Invisible Prims