Which PBR is actually PBR?

gnoop

left is Painter  with specular quality Ultra and is same sbsar material (color and roughness) exported from Designer.    Same "panorama"   environment  with same exposure value .  

Painter in "low"  settings   makes it identical  to Designer.    So which  is actually Physically based for real ?    What matches Unreal  currently ? Does anyone have an idea?

Eric Chadwick

For real? Both

Matches Unreal? Let us know.

Any idea? Somewhat. Every real-time render is opinionated, they all make tradeoffs. Also, PBR shaders all have different approximations, because PBR is not a perfect science. It’s much much better than the old Diffuse/Specular/Guessing method. But it’s still open to interpretation, decisions need to be made for speed and efficiency reasons.

gnoop

Eric Chadwick said:

For real? Both

You can check it  yourself just by changing specular quality parameter in Painter .  Default "low" looks same as in Designer.   Ultra makes  any material shine  a lot.   Especially in mid grey roughness values.       

  Imo correct intensity and spread of highlight spot  is basically main feature why we once switched to PBR pipline, right?    So I wonder how could it be so different  with different implementation and still keep PBR  title. 

  In Designer  you just can't set it Ultra, there is no corresponding  settings.   And IMO Designer is misleading you currently.  It affects roughness value you  chose a lot .

  Since every game now considers Unreal as a golden standard   I wonder what settings people set in Painter to get same as in Unreal look? 

   I haven't much time currently to test it myself since in Untreal it all depends alot on exposure  settings and sky background   and I have no idea how make it perfectly matching  to "panorama" HDRi from Substance .      Hoped someone did it already.

Eric Chadwick

Different shaders use different specular lobes. Disney GGX is a commonly used one. Im guessing that’s why you’re seeing vastly different reflections at glancing angles… tools are probably using different ways to calculate how a roughness value will scatter the “rays” of light, and simulate the scattering of light that happens from micro-facet surfaces. 

Micro-facet reflection is what a roughness parameter is simulating, the effect of tons of very small randomly angled facets (think of sand paper up close, vs far away) and how they scatter a bunch of mostly parallel light rays (the sun for example).

”Roughness” is an approximation, an optimization, and there are different ways to simulate it, each with different tradeoffs.

gnoop

Eric Chadwick said:

Different shaders use different specular lobes.

Well. Looks like it same shader  there . What's different is  "low" 4 spp vs "Ultra" 255 spp .   My guess spp  is samples per pixel.    Not sure I still understand why it produces so drastically different  shine .      And why at all it should be based on number of samples in real time shader.

poopipe

Most likely it's related to the IBL sampling which can have a fairly significant impact on perceived roughness without actually breaking the maths - in theory it can interfere with the amount and diffusion of the light coming from the sky

It's something that can be worked around but I suspect that supporting panorama images rather than properly convolved cubemaps for the IBL makes that difficult - the maths are a bit beyond me when we get to this sort of thing tbh. 


I've not looked at the shader code for either application since they adopted the Adobe materials but previously the IBL sampling in Painter was a lot more sophisticated than what Designer offered  - I wouldn't be surprised if that was still the case

gnoop

I want to test same material in Unreal  just to check how it would be looking there . Unreal became a sort of  icone of ultimate truth nowadays . If it looks some way in Unreal  the reality should bend and follow.      Just to figure out what roughness values  are correct.

Does anyone know how  to make it illuminated by same pnorama HDRi  in Unreal with same intensity with auto-exposure off and on ?        I measured  sun altitude angle in this panorama .hdr file  using sphere projection  on a sphere  it's only 16 degree  to  a ground plane.

poopipe

The panoramas supplied with painter are fudged rather than properly calibrated so you'll be eyeballing it