Physically Based Rendering: role of ambient light in BRDF

Question

I'm trying to figure out if my BRDF approach is correct or not.

// Calculate sun BRDF color
vec3 sunBrdf = brdf(tsLightSourceDir, tsEyeDir,
                    tsNormal, vtsTangent, vtsBinormal,
                    albedo.rgb,
                    NdotL, NdotV,
                    tRoughness, tMetallic, specular);

// brdf multiplied by incoming sun radiance -> color
vec3 irradiance = sunAmbientRadiance + sunDiffuseRadiance * NdotL;
vec3 brdfColor  = sunBrdf * irradiance;

// Add base ambient color
vec3 ambientColor = albedo.rgb * sunAmbientRadiance;
resultColor = ambientColor;

resultColor += brdfColor;

// Interpolate by shadow
resultColor = mix(ambientColor,
                  resultColor,
                  shadowAmount);

My question: I'm adding the ambient light 2x. 1x when calculating the ambient color and 1x by adding it to the amount of light coming into the BRDF.

I can't figure out if this is correct or not, since the BRDF needs the ambient light in my opinion since it's a part of the lighting that arrives onto the surface. But on the other hand, it's already calculated by multiplying it with the albedo color and added as a base color...

Any help is much appreciated!

Answer 1

The correct formula goes like this (in my opinion):

vec3 irradiance = sunDiffuseRadiance * NdotL;