Day: September 1, 2023

2023 week #35: SL CCUG meeting summary: glTF PBR

Posted on by Inara Pey
Reality Escape – Books, Coffee & Chairs – Oh My! – blog post †

The following notes were taken from my audio recording and chat log transcript of the Content Creation User Group (CCUG) meeting held on Thursday, August 31st, 2023.

  • The CCUG meeting is for discussion of work related to content creation in Second Life, including current and upcoming LL projects, and encompasses requests or comments from the community, together with viewer development work.
  • As a rule, these meetings are:
    • Held in-world and chaired by Vir Linden.
    • Conducted in a mix of voice and text.
    • Held at 13:00 SLT on their respective days.
    • Are subject to the schedule set within the SL Public Calendar, which includes the location for the meetings.
    • Open to all with an interest in content creation.
  • The notes herein are drawn from a mix of my own chat log and audio recording of the meeting, and are not intended to be a full transcript.

glTF Materials and Reflection Probes

Project Summary

  • To provide support for PBR materials using the core glTF 2.0 specification Section 3.9 and using mikkTSpace tangents, including the ability to have PBR Materials assets which can be applied to surfaces and also traded / sold.
  • The overall goal for glTF as a whole is to provide as much support for the glTF 2.0 specification as possible.
  • Up to four texture maps are supported for PBR Materials: the base colour (which includes the alpha); normal; metallic / roughness; and emissive, each with independent scaling.
  • In the near-term, glTF materials assets are materials scenes that don’t have any nodes / geometry, they only have the materials array, and there is only one material in that array.
  • As a part of this work, PBR Materials will see the introduction of reflection probes which can be used to generate reflections (via cubemaps) on in-world surfaces. These will be a mix of automatically-place and manually place probes (with the ability to move either).
  • The viewer is available via the Alternate Viewers page.

Further Resources

General Status

  • Cosmic Linden has been working on some permissions updates to make permissions meaningful when being addressed via LSL. This means that is a materials surface in set to No Modify, a script will not be able to change its tint, for example.
    • Support for this is currently on the glTF / PBR servers on Aditi, where it is being tested (same region names as above, just on Aditi).
    • Changes to reflect these updates will also be made to the viewer so things like the build floater correctly reflect the permissions status.
  • Runitai Linden is continuing to work on the communications bloat issue. This will utilise a new message type – GenericStreamingMessage. This will both make messages passing between the simulator and viewer more compact and also less frequent in order to reduce the load.
  • To help improve people’s awareness / avoid confusion with the updated Build floater, a new pop-up is being implemented that will be displayed and give information on the change when the floater is first opened and used with a PBR material, complete with a link to the PBR wiki page.

Mirrors

  • Mirrors are a part of the glTF / PBR materials project, but something of a separate tranche of work.
  • The idea is provide the means to have via high resolution reflections (i.e. mirrors) within a scene.
  • Initially only one active mirror surface per scene will be active for any viewer.
  • The process will use the PBR reflection probes mechanism, combined with a automated “Hero Probe” mechanism which with generate high resolution (512×512) “reflections” for the mirror.
  • The system will operate on the basis of avatar / camera proximity to a mirror surface triggering the closest reflection probe to become a “Hero Probe” for that avatar / camera. This means that if there are multiple mirrors placed within an environment, only the one closest to a given avatar / camera will be active and display the “reflections” generated by the reflection probe.
  • Depending on testing and performance, the number of mirrors might be expanded to two – one for mirror surfaces and one for Linden Water to generate high resolution water reflections where appropriate.

Summary

  • Geenz Linden hopes to start working on a version of the PBR viewer which supports mirrors very shortly.
  • The final data model for mirrors will not be available on the server end in time for the initial version of a Mirrors viewer, but will be coming later, as it is dependent on dialling-in the parameters required for the mirrors functionality based on testing.
  • Overall, the approach now taken means that mirrors will now not just be limited to planar (flat) surfaces.

Lighting / Ambient Lighting

  • Concerns continue to be raised over colour saturation / ambient colour / light within the PBR viewer within non-PBR regions. People appear to be reporting particular issues with over-saturation and with black surfaces (particularly clothing) looking “flat” or minus any clear definition.
  • It was pointed out that some of the issue may well be down to a combination of running the PBR viewer within regions that do not have the proper PBR environment adjustments, thus leading  – to some degree at least – to tone mapping being overly biased for darker colours + the adjustments made within the PBR viewer to compensate for the lack of reflection probes in non-PBR regions still requiring further tweaking + the PBR viewer generally not rendering the excess ambient light common to existing ambient lighting in non-PBR regions.
  • A lot of this is known to be an issue, and something Runitai Linden has been looking to address, as per my pervious CCUG summaries such as this one.

In Brief

  • Rider Linden noted the following updates will be available in the near future via simulator RC releases:
    • “Dog Days” update, due to go to one or more simulator RC channels during week #36 (commencing Monday, September 4th):
      • The unbinding of the Experience KVP database read / write functions from land (users will still require an Experience to access the KVP database).
      • A scripted ability to set CLICK_ACTION_IGNORE, allowing an object to be clicked-through to reach an object behind it – a flag supporting this is included in the current release viewer.
    • The still in development “Fall Colours” update, which will include:
      • llIsFriend – essentially “Is the avatar touching this object a friend of the object’s owner?”, and then act accordingly.
      • llGetInventoyDesc(ription) – a function to return a list of the contents within an rezzed object.
  • User Animats has been experimenting with a new open-source convex hull algorithm for making physics models, which he describes as probably “not suitable” for the SL mesh uploader, but which “might be useful” when working in Blender. There is a forum thread on this line of investigation got those interested.
  • A suggestion was made that as LL gather stats on the hardware users are employing to access SL, that some measure of this data is made public-facing so that creators might have a better idea of the “typical” hardware environment they need to consider, rather than assuming everyone is either running high-end or low-end systems.
    • This was put in terms of something like a list of the 10 or so most commonly used CPU / GPUs (either individually or in combination); most common RAM amounts used (8GB, 16GB, etc.), with the information made available via a web page or similar.
    • It was pointed out that some of the information might be difficult to put together as it might not be possible to accurately extrapolate or consolidate in a meaningful way.
    • However, Vir Linden thought the idea is worth poking at to see what, if anything might be done towards achieving it.
  • An animated discussion on the permissions system and No Mod objects including:
    • Why people use No Mod (such as the mistaken belief that it “prevents copybotting” + the misunderstanding users might have that while a scripted item may way have No Mod scripts, the item itself can still be modified, etc).
    • A idea for the “reset to defaults” override button for Modify object so that if a user royally messes up an object, they can click the button and restore the original look / texturing, etc., of the object (potentially very hand for Mod / No Copy objects).
    • The addition of a new attribute “Demo” which can be used to both lock an object into No Mod and add some form of “demo” indicator to it for when the user is wearing / examining it.
    • The problem with any changes with the permissions system is that it is a) already extremely complicated in its implementation; b) would require considerable care; c) is liable to be a lengthy, far-reaching project. As such, there may not be the appetite within LL to take on such work.

Next Meeting

† The header images included in these summaries are not intended to represent anything discussed at the meetings; they are simply here to avoid a repeated image of a gathering of people every week. They are taken from my list of region visits, with a link to the post for those interested.