Add a backface culling option when saving to GLTF format

[kristen.browne@…]

GLTF materials have a backface culling flag that tells the renderer whether to enable that option. The default is true, but an option to make it false would help for non-closed surfaces.

From: "Browne, Kristen (NIH/NIAID) [C]"
Subject: RE: [EXTERNAL] Re: gltf smoothing attribute:
Date: May 11, 2023 at 5:04:39 PM PDT
To: Tom Goddard

I’m not too sure exactly how things are computed! I actually stumbled into this because when I was building the mesh repair workflow, I use the STL that is created from the GLB files. Those files were really faceted in the viewer because the “smoothing” information was stripped. Then it came up again when I needed to remove the default “smooth shading” preference in my renderings for devices etc. and saw that indeed this was being applied to the GLBs from ChimeraX . Troubleshooting errors in the mesh repair process I’ve been working on gave me the opportunity to really scrutinize the outputs in a way there just wasn’t time for before.

One other thing that would be a totally optional feature request, would be to have a ChimeraX GUI option when outputting a glb to turn backface culling off. By default, most viewers optimize performance by not rendering the backfaces. When Phil was creating custom models that had a patch of surface in ChimeraX, they looked invisible when put in the viewer when viewed from the back. Same on Babylon and other GLTF viewers for web. I fixed them for him by extruding a second face. I could also manually update the gltf setting for backface culling. It is a gltf property of the material as they even have a toggle for it in the Babylon inspector:
<image001.png>

This is something that we can also do on our end, but it might be of wider use to your users that are also wanting to export models that have a surface like this and view it in a glb viewer like Babylon. I leave it up to you if it’s something you would like to incorporate!

K

[kristen.browne@…]

One other example of how this is used is when Phil wants to  go inside a surface model.  This sometimes comes up when you dive in and look at a ribbon that inside the surface.  Once you're inside, depending on the development environment/viewer, you won't be able to see the surface anymore when you're inside.

-----Original Message-----
From: ChimeraX <ChimeraX-bugs-admin@cgl.ucsf.edu>
Sent: Thursday, May 11, 2023 8:11 PM
Cc: goddard@cgl.ucsf.edu; Browne, Kristen (NIH/NIAID) [C] <kristen.browne@nih.gov>
Subject: [EXTERNAL] [ChimeraX] #9001: Add a backface culling option when saving to GLTF format

#9001: Add a backface culling option when saving to GLTF format
------------------------------+----------------------------------
 Reporter:  kristen.browne@...  |               Owner:  Tom Goddard
     Type:  enhancement       |              Status:  assigned
 Priority:  moderate          |           Milestone:
Component:  Input/Output      |             Version:
 Keywords:                    |          Blocked By:
 Blocking:                    |  Notify when closed:
 Platform:  all               |             Project:  ChimeraX
------------------------------+----------------------------------
 GLTF materials have a backface culling flag that tells the renderer  whether to enable that option.  The default is true, but an option to make  it false would help for non-closed surfaces.

 From: "Browne, Kristen (NIH/NIAID) [C]"
 Subject: RE: [EXTERNAL] Re: gltf smoothing attribute:
 Date: May 11, 2023 at 5:04:39 PM PDT
 To: Tom Goddard

 I'm not too sure exactly how things are computed!  I actually stumbled  into this because when I was building the mesh repair workflow, I use the  STL that is created from the GLB files.  Those files were really faceted  in the viewer because the "smoothing" information was stripped.  Then it  came up again when I needed to remove the default "smooth shading"
 preference in my renderings for devices etc. and saw that indeed this was
 being applied to the GLBs from ChimeraX .   Troubleshooting errors in the
 mesh repair process I've been working on gave me the opportunity to really  scrutinize the outputs in a way there just wasn't time for before.

 One other thing that would be a totally optional feature request, would be  to have a ChimeraX GUI option when outputting a glb to turn backface  culling off.  By default, most viewers optimize performance by not  rendering the backfaces.  When Phil was creating custom models that had a  patch of surface in ChimeraX, they looked invisible when put in the viewer  when viewed from the back.  Same on Babylon and other GLTF viewers for  web.  I fixed them for him by extruding a second face.  I could also  manually update the gltf setting for backface culling.  It is a gltf  property of the material as they even have a toggle for it in the Babylon
 inspector:
 <image001.png>

 This is something that we can also do on our end, but it might be of wider  use to your users that are also wanting to export models that have a  surface like this and view it in a glb viewer like Babylon.  I leave it up  to you if it's something you would like to incorporate!

 K

--
Ticket URL: <https://www.rbvi.ucsf.edu/trac/ChimeraX/ticket/9001>
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[Tom Goddard]

Done.

I added a backfaceCulling option (default true) to the save command for gltf format. So using "save myscene.glb backfaceCulling false" will allow you to go inside surfaces and view the interior. Maybe that should be the default. But it is a standard graphics performance optimization to not render triangles seen on their inside sides. Changing that default so it does render those will slow rendering down a little which could reduce the size of model that can be viewed in VR. So for now I will leave the default as backfaceCulling true which is what the GLTF standard uses as the default.

If you wish to use this option in the NIH3D pipeline scripts for certain models, describe which ones and Eric can look at changing the scripts.

[kristen.browne@…]

I think this is great.  True should absolutely be the default, but this will let Phil set the option himself when he's exporting certain models that need to go in VR etc.

Thanks!


-----Original Message-----
From: ChimeraX <ChimeraX-bugs-admin@cgl.ucsf.edu>
Sent: Friday, May 12, 2023 9:06 PM
Cc: goddard@cgl.ucsf.edu; Browne, Kristen (NIH/NIAID) [C] <kristen.browne@nih.gov>; meng@cgl.ucsf.edu; pett@cgl.ucsf.edu
Subject: [EXTERNAL] Re: [ChimeraX] #9001: Add a backface culling option when saving to GLTF format

#9001: Add a backface culling option when saving to GLTF format
---------------------------------------+-------------------------
          Reporter:  kristen.browne@...  |      Owner:  Tom Goddard
              Type:  enhancement       |     Status:  closed
          Priority:  moderate          |  Milestone:
         Component:  Input/Output      |    Version:
        Resolution:  fixed             |   Keywords:
        Blocked By:                    |   Blocking:
Notify when closed:                    |   Platform:  all
           Project:  ChimeraX          |
---------------------------------------+-------------------------
Changes (by Tom Goddard):

 * cc: Elaine Meng, pett (added)
 * status:  assigned => closed
 * resolution:   => fixed


Comment:

 Done.

 I added a backfaceCulling option (default true) to the save command for  gltf format.  So using "save myscene.glb backfaceCulling false" will allow  you to go inside surfaces and view the interior.  Maybe that should be the  default.  But it is a standard graphics performance optimization to not  render triangles seen on their inside sides.  Changing that default so it  does render those will slow rendering down a little which could reduce the  size of model that can be viewed in VR.  So for now I will leave the  default as backfaceCulling true which is what the GLTF standard uses as  the default.

 If you wish to use this option in the NIH3D pipeline scripts for certain  models, describe which ones and Eric can look at changing the scripts.

--
Ticket URL: <https://www.rbvi.ucsf.edu/trac/ChimeraX/ticket/9001#comment:2>
ChimeraX <https://www.rbvi.ucsf.edu/chimerax/>
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CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and are confident the content is safe.