Change Details

**System Information** Operating system: Windows-10-10.0.19043-SP0 64 Bits Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.07 **Blender Version** Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: `rBf1cca3055776` Worked: (newest version of Blender that worked as expected) **Short description of error** The Principled BSDF in Blender uses the metalness workflow. This means that we don't have direct control over the F(0) reflectivity of the dielectric parts of the mesh, which is why Blenders Principled BSDF additionally also has a specular parameter to control the F(0) reflectivity of these areas. Since with metallic materials the F(0) reflectivity is directly controlled by the Base color this means that for metallic areas the specular parameter should not have any influence on the reflectivity of the material whatsoever. However it does, as by lowering the specular parameter on the Principled BSDF visibly reduces the reflectivity on the edges of metals in a physically unexplainable way. When setting the specular value to 0 the Principled BSDF then uses the F(0) value as reflectivity at all angles. I am not sure if this is a bug or a feature, but even if this were a feature there isn't a single source which mentions how the specular parameter influences the Fresnel equation (or in the case of the Principled BSDF Schlick's approximation) mathematically, so if you know where that would be documented please share it with us. **Exact steps for others to reproduce the error** {F12930396} Test file with cylinder, specular value increasing from bottom to top, raised to the 4th power to make effect more visible.

**System Information** Operating system: Windows-10-10.0.19043-SP0 64 Bits Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.07 **Blender Version** Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: `rBf1cca3055776` Worked: (newest version of Blender that worked as expected) **Short description of error** The Principled BSDF in Blender uses the metalness workflow. This means that we don't have direct control over the F(0) reflectivity of the dielectric parts of the mesh, which is why Blenders Principled BSDF additionally also has a specular parameter to control the F(0) reflectivity of these areas. Since with metallic materials the F(0) reflectivity is directly controlled by the Base color this means that for metallic areas the specular parameter should not have any influence on the reflectivity of the material whatsoever. However it does, as by lowering the specular parameter on the Principled BSDF visibly reduces the reflectivity on the edges of metals in a physically unexplainable way. When setting the specular value to 0 the Principled BSDF then uses the F(0) value as reflectivity at all angles. I am not sure if this is a bug or a feature, but even if this were a feature there isn't a single source which mentions how the specular parameter influences the Fresnel equation (or in the case of the Principled BSDF Schlick's approximation) mathematically, so if you know where that would be documented please share it with us. **Exact steps for others to reproduce the error** {F12930396} Test file with cylinder, specular value increasing from bottom to top, raised to the 4th power to make effect more visible. Now even if this were a bug I think, that we should keep it as, being able to control the Fresnel like this is a very handy feature however there is a problem, which is that the specular value does not control the reflectivity of the Principled BSDF if the transmission value is 1. In the below file for both planes the specular value increases from left to right, while the top has transmisson=1 and the bottom plane has metallic=1, the reflection of both planes have been reduced to show just the glossy reflection. {F12930429} As can be clearly seen on the bottom plane the glossy reflection increases with increasing specularity however on the top plane stays the same.

**System Information** Operating system: Windows-10-10.0.19043-SP0 64 Bits Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.07 **Blender Version** Broken: version: 3.0.0, branch: master, commit date: 2021-12-02 18:35, hash: `rBf1cca3055776` Worked: (newest version of Blender that worked as expected) **Short description of error** The Principled BSDF in Blender uses the metalness workflow. This means that we don't have direct control over the F(0) reflectivity of the dielectric parts of the mesh, which is why Blenders Principled BSDF additionally also has a specular parameter to control the F(0) reflectivity of these areas. Since with metallic materials the F(0) reflectivity is directly controlled by the Base color this means that for metallic areas the specular parameter should not have any influence on the reflectivity of the material whatsoever. However it does, as by lowering the specular parameter on the Principled BSDF visibly reduces the reflectivity on the edges of metals in a physically unexplainable way. When setting the specular value to 0 the Principled BSDF then uses the F(0) value as reflectivity at all angles. I am not sure if this is a bug or a feature, but even if this were a feature there isn't a single source which mentions how the specular parameter influences the Fresnel equation (or in the case of the Principled BSDF Schlick's approximation) mathematically, so if you know where that would be documented please share it with us. **Exact steps for others to reproduce the error** {F12930396} Test file with cylinder, specular value increasing from bottom to top, raised to the 4th power to make effect more visible. Now even if this were a bug I think, that we should keep it as, being able to control the Fresnel like this is a very handy feature however there is a problem, which is that the specular value does not control the reflectivity of the Principled BSDF if the transmission value is 1. In the below file for both planes the specular value increases from left to right, while the top has transmisson=1 and the bottom plane has metallic=1, the reflection of both planes have been reduced to show just the glossy reflection. {F12930429} As can be clearly seen on the bottom plane the glossy reflection increases with increasing specularity however on the top plane stays the same.