I want to avoid IBL (image based lighting), however my scenes are way too dark - especially close-to-mirror like surfaces, which get little contributions from other direct light sources in the scene.
So I was thinking that I should add some sort of scene light - with single color defined in the scene. How do I calculate the contribution of such light based on normal and view directions, material albedo, roughness and metallness, and the scene color? Is there any standard or typical equation for that?
Note that I would like it view-dependant.
Edit:
All the balls in this picture should have approximately the same apparent brightness, but the smooth metal balls are way darker.
I am using smith+ggx brdf, possibly modified. Here is the whole fragment shader: https://gist.github.com/malytomas/b882c27c324a4f27ff56780717c9e4b2#file-cage_shader_engine_standard-glsl_fragment-glsl-L347 Line 347 is where I would like to add additional term to compensate for the absence of IBL.