To Lambert or to not Lambert...

While publishing on mobile, is there a difference in performance in using Lambert or not using it and writing my own vert/frac?

Let's say I have a mesh that is not lit, and only take vertex color and/or a texture?

 

Thanks, was wondering. Any idea how much of a difference it is? Is there a way to write vertex lighting as efficient as possible? Frankly, the pixel shaders are rather destructive on iPhone 4.

 

Yeah, but the issue is we need to use vertex color, and not a texture, so I need to write custom stuff anyway.

 

You're probably aware of this, but just because I like to nitpick, "Lambert" is really just the part of lighting that does

Code (csharp):

1.  
2. NdotL = dot(normalizedSurfaceNormal, normalizedDirectionToIncomingLight);
3. litCol = albedo * lightCol * NdotL;
4.  

As soon as you do lighting you'll always have this term in there somewhere, whether custom vert/frag or built-in Surface Shaders, whether your lighting is per-vertex or per-pixel, whether you add a specular term or not.. Even for an alternative diffuse term "other than Lambert" such as Oren-Nayer this term is still in there somewhere!

Just to ensure that no further misconceptions about Lambert enter the airwaves

 

Well, doing lighting per vertex instead of per pixel mean I only do this math once per vertex instead of one per pixel. That's a HUGE performance boost. Does Lambert allow per-vertex lighting?

 

YES Lambert is just the albedo*NdotL formula, whether the N part is per-vertex normal or per-pixel normal is your choice essentially.

 

How am I suppose to set Lambert to not perform any light math per pixel?

 

At your current stage of understanding I'd suggest you use the built-in "VertexLit" surface shaders and the VertexLit (as opposed to Forward or Deferred) rendering path and you'll be good to go

If you do insist regardless on writing your own vert+frag shaders there's not much Unity or ShaderLab-specific to worry about, any of the 1000s of web tutorials on basic vertex lighting will do the trick and the Unity wiki I believe have all or most of the vertex-lit vert+frag shaders / templates you should realistically need.

If you run into a specific issue, you might wanna post a new specific question with your shader code that's troubling you