Day: November 4, 2023

2023 week #44: SL CCUG meeting summary: PBR

Posted on by Inara Pey
Shades of Autumn, September 2023 – blog post †

The following notes were taken from my audio recording and chat log transcript of the Content Creators User Group (CCUG) meeting held on Thursday, November 2nd, 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, in accordance with the dates and times given in the the SL Public Calendar, which also includes the location for the meetings.
    • Conducted in a mix of voice and text..
    • Open to all with an interest in content creation.
  • The notes herein are a summary of topics discussed and are not intended to be a full transcript.

Viewer Updates

The glTF / PBR RC viewer updated to version 7.0.1.6658224456 on November 2nd, bringing it into parity with the current release viewer and built via Github Actions.

The rest of the official viewers in the pipeline remain as:

  • Release viewer, version 6.6.16.6566955269, promoted October 25 (formerly the GHA RC viewer).
  • Release channel cohorts:
  • Project viewers:

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

Status Update

Server-side deployment

  • The simulator code supporting PBR Materials was deployed to the BlueSteel and LeTigre simulator RC channels, making it “live” across some 3,000 simulators.
  • This has seen a number of additional bug reports filed, but currently nothing which has been seen as constituting a major blocker to further deployment.
  • At the time of the meeting, it was hoped that the PBR code could be deployed to all of the RC channels simhosts on Wednesday, November 8th, 2023. This is seen as the best way to test for additional cases of non-PBR content suffering breakage which may have thus far slipped through the net.
  • If things continue as planned, the aim is to have PBR support on the simhosts fully deployed “by Thanksgiving”.

Viewer Updates

  • The PBR viewer has been updated to build via the new Github Action process, marking it as up-to-date with the current release viewer (version 6.6.16.6566955269, October 25th, at the time of writing).
  • It is possible that one of the Maintenance RC viewers may be pushed to de facto release ahead of the PBR viewer in order to correct a statistics reporting issue.
    • At the time of the meeting, a final decision on this has yet to be made. However, if this proves to be the case, and if LL decide to maintain the 2-week minimum period between viewer promotions, this could mean the PBR viewer might not be released until after the simulator code is grid-wide.
  • The PBR viewer release is also dependent upon whether or not any remaining reported / open issues are considered serious enough to require fixing ahead of any promotion.
    • Currently, there is one blocker which is under investigation: if the PBR viewer is used, and then a swap is made to using a non-PBR viewer, then it is possible some objects may not show-up on logging in, and will never show up until object cache is cleared.
  • For those interested – this is the list of currently open issues for PBR.
  • The current PBR RC viewer replaces the term “Materials” in the Build / Edit floater Texture tab with Blinn-Phong. Whilst this is the technically correct term for the current implementation of materials support in SL and was seen as a means of differentiating between the current materials support and PBR, the switch to the term has been raised as potentially confusing to users not deeply versed in graphics  / rendering but who are familiar with using and applying current materials maps. As such, the use of an alternate term has been requested.

Tone Mapping and Full Bright Issues

  • A recently-reported issue is with tone mapping not applying correctly to Full Bright objects, resulting in darker colours / blacks being crushed and white highlights being blown out.
  • This has been highlighted in BUG-234506 and this forum thread, where it is reported as an issue facing content creators trying to produce advertising images for their products for use on in-world vendor boards, etc. However, the issue has the potential to affect SL photography in general, where snapshots are taken to be uploaded for display in-world as textures (e.g. as art, “family” snapshots, etc.).
  • The problem is the result of tone mapping being applied to such textures twice:
    • The first time as a result of tone mapping being enabled (and captured) when the snapshot is taken.
    • The second time as a result of the uploaded texture being rendered with tone mapping active in the viewer.
  • This is seen as “expected behaviour”, and the lighting model will not be changed for dealing with Full Bright (e.g. by making it a straight pixel pass-through).
  • This means the current work-around is to use the No Post Build menu option, thus:
    • Edit the object using Full Bright to open the Build  / Edit floater.
    • Go to menu bar → Build → Options and enable No Post – this will try off tone mapping and exposure, and will remain active as long as the Build / Edit floater is open.
    • Take the snapshot.
    • Close the Build / Edit floater.
  • As this workaround is seen as heavy-handed (and also not helpful to those taking photos who may need to disable tone mapping at times, but who are unfamiliar with the Build / Edit floater and Build menu), it has been requested to incorporate a toggle checkbox for No Post directly into the snapshot floater.
  • Runitai Linden has also proposed the addition of a HDRI export to the 360º Snapshot floater.

General Notes

  • The viewer performance issue on older versions of MacOS has been addressed, but it is not clear if the fixes work with Apple silicon SoC, pending further tests.
  • It is acknowledged that there will be a learning curve among all users where PBR is concerned due to the level of changes involved in the lighting model (e.g. objects with a specular map – even indoors – having a blue sheen to them, due to reflecting the ambient environment; an issue which can be fixed through the correct placement of reflection probes indoors).
    • Efforts are being made to ensure cases like this are being covered in the PBR documentation being put together by LL.
  • It was re-iterated that there will be follow-on glTF work following PBR materials (see the general roadmap, below), with it being noted that some would allow the implementation of hierarchical structures which could allow for options such as arbitrary pivot points in meshes, whilst adoption of the glTF specifications for animations could result expanded animation capabilities, etc.
  • A number of requests for new features (e.g. the ability to be able to simulate Linden water on surfaces via materials). These were noted as all having pre-requisites and potential limiters on them, so while they are not refused, mention of them here will be held over until LL have determined if and how they (and their pre-requisites) might fit into the overall roadmap.
  • Whilst concerns remain about Apple simply ceasing to support OpenGL, thus driving a potential need to switch the viewer away from using OpenGL to using Vulkan / MoltenVK, this is not seen as an immediate priority compared to moving ahead with further glTF work. Which is not to say LL won’t move the viewer to alternate graphics API as the glTF work progresses beyond scene import work (see below).

Likely Roadmap for glTF

  • Complete and deploy the current PBR materials work.
  • Resume work on real-time mirrors and terrain support for glTF materials. In brief, these comprise:
    • Mirrors: providing the means to have mirrors within scenes to reflect their immediate surroundings. These will leverage a “hero” reflection probe concept (512×512 resolution), with one such probe per scene being active for any given avatar, based on the avatar / camera distance from the mirror.
    • Terrain support: providing the means to apply glTF materials to terrain as a viewer-side effect to improve the appearance of the SL terrain. Note that this is not PBR terrain painting.
  • Alongside the mirrors / terrain work will be a period of PBR Materials maintenance work to fix reported bugs / those issues still open at the time of release.
  • Also start to develop a prototype for glTF scene import – with no overall time frame for the latter being indicated.
  • Once there is an initial prototype for glTF scene import, he Lab will proceed in much the same was as for PBR materials: an iterative development cycle which fully engages the user community / content creators.

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.