Problem with Basic Diffuse Lighting

Question

So recently I have been learning how to implement Diffuse Lighting in DirectX and I have done so with the following code:

float4 PS(VS_OUTPUT input) : SV_TARGET
{
    input.normal = normalize(input.normal);

    float4 diffuse = ObjTexture.Sample(ObjSamplerState, input.TexCoord);

    float3 finalColor;

    finalColor = diffuse * light.ambient;
    finalColor += saturate(dot(light.dir, input.normal) * light.diffuse * diffuse);

    return float4(finalColor, diffuse.a);
}

which has produced the following results:

Before I progress any further with specular lighting I wanted to clean up my code a little so I re-implemented this with a function and few changes.

float3 DirectDiffuseBRDF(float3 diffuseAlbedo, float nDotL)
{
    return (diffuseAlbedo * nDotL);
}

float4 PS(VS_OUTPUT input) : SV_TARGET
{
    input.normal = normalize(input.normal);

    float4 diffuseAlbedo = ObjTexture.Sample(ObjSamplerState, input.TexCoord);

    float nDotL = saturate(dot(input.normal, light.dir));

    float3 diffuseLighting = DirectDiffuseBRDF(diffuseAlbedo, nDotL);

    return float4(diffuseLighting, diffuseAlbedo.a);
}

Which produces:

As you can see the modified code has it's diffuse lighting a little different compared to the original. What am I missing from the original code to get it back to normal?

Answer 1

I have combined the before and after code and came up with this:

float3 DirectDiffuseBRDF(float3 diffuseAlbedo, float nDotL)
{
    return (diffuseAlbedo * nDotL);
}

float4 PS(VS_OUTPUT input) : SV_TARGET
{
    input.normal = normalize(input.normal);

    float4 diffuseAlbedo = ObjTexture.Sample(ObjSamplerState, input.TexCoord);

    float nDotL = dot(input.normal, light.dir);

    float3 diffuseLighting = diffuseAlbedo * light.ambient;

    diffuseLighting += saturate(DirectDiffuseBRDF(diffuseAlbedo, nDotL) * light.ambient);

    return float4(diffuseLighting, diffuseAlbedo.a);
}

I haven't tested it but it should work.