SL project updates 16 12/3: invisiprims

Invisiprims: as they were with ALM disabled (left) and ALM enabled (right) and as they appear now, with or without ALM enabled (LL official viewer)
Invisiprims: with ALM disabled (left) and ALM enabled (right); and as they appear now in the official viewer, with or without ALM enabled (click for full size, if required)

As noted in my week #11 update, the current release of the LL viewer now effectively “breaks” the remaining invisiprim capability in the viewer, with any object or surface using them rendered as either solid grey or black, something which is seen as less than optimal with regards to long-standing in-world content, prompting some debate as who should be done with invisiprims going forward.

To understand what has been discussed, and what is likely to be done, it is necessary to dip back into some history.


One upon a time, Invisiprims were the means of achieving an alpha mask effect. For example, their use in footwear meant that an avatar’s feet could be masked to prevent them showing through shoes and boots. They could also be used in-world as well, a typical example being their use to mask Linden Water from being seen inside boat hulls or things like dry docks – one of the most famous examples being the dry dock at Nautilus (shown below).

As it used to be: the Nautilus dry dock uses an invisiprim to mask the Linden Water - but for the last few years this has onlt worked for viewers with Advanced Lighting Model (ALM) disabled
As it used to be: the Nautilus dry dock uses an invisiprim to mask the Linden Water. For the last several years, this has only worked when the Advanced Lighting Model (ALM) in the viewer is disabled

Invisiprims were able to do this by making use of two unique texture UUIDs within the viewer which, when called, would act as alpha masks. However, this always came as a cost to rendering, and could lead to unpredictable results (e.g. glitches with rendering, odd interactions between the invisiprim textures and other textures, etc.). Because these issues became particularly problematic when using some of the advanced rendering capabilities (what is now called the Advanced Lighting Model or ALM) in the viewer, a decision was taken a number of years ago to have ALM ignore the alpha masking effect of the invisiprim texture UUIDs.

Thus, anyone running the viewer with ALM enabled for the last several years  has not seen the masking effects of invisiprims; avatar body parts show through wearable items which use them, for example (hence the adoption of more efficient alpha layers by clothing and accessory designers). Nor do in-world invisiprims act a masks for things like Linden Water when viewed with ALM active (as illustrated below), although they would still alpha mask if ALM was disabled in the viewer.

As it has tended to be: the Nautilus dry dock uses an invisiprim to mask the Linden Water, the texture of which is completely ignored by the viewer when rendering with ALM enabled.
Following the changes made a few years ago to the Advanced Lighting Model, the “magic” invisiprim texture UUIDs are ignored during rendering, with the result that they no longer mask things like Linden Water when seen in a viewer with ALM enabled

While this latter point – the lack of ability to hide things like Linden Water from view – may have appeared less than perfect at the time the changes were made, it has over the ensuing years become accepted behaviour when seen in-world.  So what has now changed to once again make invisiprims a subject of discussion?

The New Problem and Its Proposed Solution

In short, a recent change to the viewer rendering system, (found in the current release viewer, means that anything using the invisiprim texture UUIDs is now seen as a sold grey or black surface / object regardless as to whether ALM is enabled in the viewer or not. This has led a lot of long-standing, No Mod in-world content looking distinctly odd and unsightly (shown below, again using the Nautilus dry dock).

The new invisiprim issue is that regradless of whether a viewer is running with ALM disabled (l) or enabled (r), worn or in-world objects using them now appear either solid grey or black (click image for full size, if required)
A change to the release viewer means that invisprims now render as solid grey or black surfaces / objects whether or not ALM is enabled in the viewer. With in-world content, this has led to some unsightly results, such as the Nautilus dry dock looking like it has been filled with cement (click image for full size, if required)

BUG-11562 was raised highlighting this latter impact to in-world content, with a request that the change be updated so that any surface using the “magic” invisiprim UUIDs is simply rendered as “invisible” (i.e. transparent, as is the case when running with ALM enabled). There has also been some debate among TPV developers about how to adopt the Lab’s code change, as well as the matter being discussed at both the Open-Source Developer meeting and the TPVD meeting held on March 25th, 2016 (audio extract below).

The latter discussions have resulted in both the Lab and TPV developers agreeing that the best solution would be to follow the BUG-11562 suggestion, and have surfaces and objects using the invisiprim UUIDs render and transparent objects whether or not ALM is enabled in the viewer.

A change to support this has already be submitted to the Lab to achieve this. Subject to further testing, it, or a solution similar to it, is likely to be integrated into a future viewer update.

8 thoughts on “SL project updates 16 12/3: invisiprims

    1. Some did. I believe the most recent round of human starter classic avatars avoid them, however (although admittedly, I’ve not check all of them).


        1. Yup, was aware of the old library avatars. But as you say, these are no longer offered to incoming new users, hence why I only commented on the recent classic avatars 🙂 .


  1. I still see many avatars with heeled shos and boots using invisprims rather than more recent alpha masks.. presumably in some cases on no mod shoes. I hope the proposed solution will help fix this glitch whch has looked ugly for the last few years.


    1. This solution will mean that those running with ALM disabled (and who I think are the ones who still tend to still use footwear reliant on invisiprims) will see the same issue as you and I. This may encourage them to see if their footwear can be updated (some maker so provide alpha-based updates for their boots, etc.), or experiment with using alphas. Of course, the later aren’t a total cure-all for every situation, but they are an alternative.


  2. I got here hoping to find a way of keeping linden water out of a cellar and a dry dock. thought I’d found the answer and now I see the invisiprims no longer have that property. I accept there might be good reasons for this though I wish there was another way to achieve the effect should in the nautilus dock


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