Specular-Glossiness Pbr Material plugin to override METALLICWORKFLOW

Charge · July 31, 2023, 5:03pm

Hi,
I’d like to be able to switch modes from a metallic-roughness material to a specular glossy material on the fly. I’d also like to use a singular ORM texture for both, which currently forces the material into metallic-roughness mode.

In principle, when in specular-glossy mode I would like to get the:

Occlusion from the Red channel of the ORM texture (already possible in metallic mode)
Specular as an intensity/white value from the Green Channel (roughness in metallic mode)
Glossiness as an intensity/white value from the Blue Channel (metalness in metallic mode)

I was thinking of creating a MaterialPlugin in order to achieve this, and was hoping for some guidance from the forum.

It looks to me that the metal workflow is initiated by setting the define METALLICWORKFLOW. This happens if certain values are set within the PBR material.
Would I simply be able to:

#undef METALLICWORKFLOW in my plugin to enable the specular-glossy workflow?
Use the material plugin to set where it gets the colors for the specular-glossy workflow?

I realise there will be a number of headaches within the above steps, but I was wondering if there are any other major steps that I haven’t considered? Or any advice that you would recommend?

Thanks

carolhmj · July 31, 2023, 7:13pm

cc @Evgeni_Popov

Evgeni_Popov · August 1, 2023, 8:29am

It may work…

Here’s what is conditioned by METALLICWORKFLOW in the js code:

github.com

BabylonJS/Babylon.js/blob/master/packages/dev/core/src/Materials/PBR/pbrBaseMaterial.ts#L2178-L2198


      
          if (defines.METALLICWORKFLOW) {

              TmpColors.Color3[0].r = this._metallic === undefined || this._metallic === null ? 1 : this._metallic;

              TmpColors.Color3[0].g = this._roughness === undefined || this._roughness === null ? 1 : this._roughness;

              ubo.updateColor4("vReflectivityColor", TmpColors.Color3[0], 1);

          

              const ior = this.subSurface?._indexOfRefraction ?? 1.5;

              const outsideIOR = 1; // consider air as clear coat and other layers would remap in the shader.

          

              // We are here deriving our default reflectance from a common value for none metallic surface.

              // Based of the schlick fresnel approximation model

              // for dielectrics.

              const f0 = Math.pow((ior - outsideIOR) / (ior + outsideIOR), 2);

          

              // Tweak the default F0 and F90 based on our given setup

              this._metallicReflectanceColor.scaleToRef(f0 * this._metallicF0Factor, TmpColors.Color3[0]);

              const metallicF90 = this._metallicF0Factor;

          

              ubo.updateColor4("vMetallicReflectanceFactors", TmpColors.Color3[0], metallicF90);

          } else {

              ubo.updateColor4("vReflectivityColor", this._reflectivityColor, this._microSurface);

          }

So, if you undef METALLICWORKFLOW, you will need to set vReflectivityColor to the correct value in the plugin material’s bindForSubMesh method.

I don’t see any other problems so far, but it’s of course untested and unsupported, so do it at your own risk

Charge · August 1, 2023, 9:34am

Thank you, that was really useful information

Topic		Replies	Views
Is it possible to create specular glossiness workflow PBR material in NodeMaterial? Questions	12	1106	April 28, 2022
Best workflow for more control over specular reflections Questions	1	227	June 27, 2023
Metallic Roughness / Specular Glossiness gltf sample assets Questions	3	351	January 12, 2024
Metallic and roughness textures in PBR Questions material , pbr	2	458	December 4, 2023
MetallicRoughness workflow conversion to SpecularGlossiness Questions	4	129	April 19, 2024

Specular-Glossiness Pbr Material plugin to override METALLICWORKFLOW

Related topics