PBRLighting does not support per-vertex lighting?

Ali_RS · April 15, 2020, 9:15am

Hi

In Lighting.j3md we have a parameter to enable per-vertex lighting

jMonkeyEngine/jmonkeyengine/blob/b92e7a0abe88e0fea64d1249fcc61f5b420defa7/jme3-core/src/main/resources/Common/MatDefs/Light/Lighting.j3md#L7


MaterialDef Phong Lighting {
    MaterialParameters {
        // Compute vertex lighting in the shader
        // For better performance
        Boolean VertexLighting
        // Alpha threshold for fragment discarding
        Float AlphaDiscardThreshold 
        // Use the provided ambient, diffuse, and specular colors
        Boolean UseMaterialColors
        // Use vertex color as an additional diffuse color.
        Boolean UseVertexColor

but we do not have it in PBRLighting:

github.com

jMonkeyEngine/jmonkeyengine/blob/master/jme3-core/src/main/resources/Common/MatDefs/Light/PBRLighting.j3md

MaterialDef PBR Lighting {

    MaterialParameters {

        // Alpha threshold for fragment discarding
        Float AlphaDiscardThreshold (AlphaTestFallOff)

        //metalness of the material
        Float Metallic : 1.0
        //Roughness of the material
        Float Roughness : 1.0        
        // Base material color
        Color BaseColor : 1.0 1.0 1.0 1.0
        // The emissive color of the object
        Color Emissive        
        // the emissive power
        Float EmissivePower : 3.0        
        // the emissive intensity
        Float EmissiveIntensity : 2.0

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Does anybody know why PBRLighting does not support per-vertex lighting? And should we add it?

pspeed · April 15, 2020, 2:18pm

I can’t speak to whether or not it was an oversight but I guess per vertex lighting is going to be easier with phong lighting since in regular frag shading (non-vertex) you are just interpolating the light dir and and so interpreting a precalculated light value is not so bad.

I imagine it’s word on PBR where the IBL is being sampled, etc… I can’t imagine it looking really bad. I have no evidence that it’s true, though.

Could be that it’s just a lot more varyings to manage because the lighting calculations are not as simple in the fragment shader.

sailsman63 · April 15, 2020, 2:55pm

It doesn’t look as if it’s a matter of “Supporting” anything. I’m not a shader expert, but skimming through lighting.frag: this is just a flag for whether the Shader should rely on an externally generated pre-computed sum of the various lighting components , (per vertex) or generate the data itself. As the comment says, "For better performance"

I’d suspect that the way PBR works, this data has to be computed in the shader, so no “Option” to do things another way.

pspeed · April 15, 2020, 3:13pm

In lighting.j3md, if you select vertex lighting the lighting information is calculated per vertex and interpolated over the fragments. If vertex lighting is off then the lighting is calculated per fragment. Vertex lighting also skips bump mapping, normal maps, etc…

Considering that in PBR, the roughness, metalness, etc. are all directional on some level and definitely use the indirect lighting information, I suspect that vertex lighting would look very bad if these were interpolated over a whole scan line.