Is it more qualitative to calculate light direction manually or using WorldSpaceLightDir(vertex)?

Questions & Answers
1

I’m wondering how to get best vizualization, and I calculate light direction in my vertex function using function WorldSpaceLightDir, and all the rest calculations are in the fragment function. However, I also could have calculated light direction in fragment function using: lightDir = normalize(_WorldSpaceLightPos0.xyz)(if we consider also point lights, code will be longer of course); . Which one gives best visual effects? Or is the difference negligible?

2

Decide yourself:

// Taken from \Unity\Editor\Data\CGIncludes\UnityCG.cginc

// Computes world space light direction, from world space position
inline float3 UnityWorldSpaceLightDir( in float3 worldPos )
{
	#ifndef USING_LIGHT_MULTI_COMPILE
		return _WorldSpaceLightPos0.xyz - worldPos * _WorldSpaceLightPos0.w;
	#else
		#ifndef USING_DIRECTIONAL_LIGHT
		return _WorldSpaceLightPos0.xyz - worldPos;
		#else
		return _WorldSpaceLightPos0.xyz;
		#endif
	#endif
}

// Computes world space light direction, from object space position
// *Legacy* Please use UnityWorldSpaceLightDir instead
inline float3 WorldSpaceLightDir( in float4 localPos )
{
	float3 worldPos = mul(_Object2World, localPos).xyz;
	return UnityWorldSpaceLightDir(worldPos);
}

If you only need directional lighting it’s probably simpler to use _WorldSpaceLightPos0.xyz directly.
Also note that WorldSpaceLightDir has a “Legacy note” so you shouldn’t use it at all ^^.