"Unity3D ShaderLab explain the development of actual combat" in Chapter 4 basic illumination model

Diffuse (Lambert)

• Lum = C * max(0, cos(L, N))
  • Lum: diffuse reflective brightness.
  • C: diffuse reflective intensity (diffuse reflective color).
  • L: direction of incident light.
  • N: normal direction.

Transmitting mirror (Phong)

• Lum = C * pow(max(0, cos(R, V)), gloss)
  • Lum: high brightness.
  • C: high light intensity (highlight color).
  • R: the direction of the reflected light.
  • V: viewing direction.
  • gloss: mirror smoothness.

Half-size vector (BlinnPhong)

• Lum = C * pow(max(0, cos(H, N)), gloss)
  • Lum: high brightness.
  • C: high light intensity (highlight color).
  • H: half-size vector.
  • N: normal direction.
  • gloss: mirror smoothness.

Function illumination inside Unity

• Forward under diffuse lighting function:

inline fixed4 LightingLambert(SurfaceOutput s, fixed3 lightDir, fixed atten){
	fixed diff = max(0, dot(s.Normal, lightDir));
	fixed4 c;
	c.rgb = s.Albedo * _LightColor0.rgb * (diff * atten * 2);
	c.a = s.Alpha;
	return c;
}

• Forward functions at high light:

inline fixed4 LightingBlinnPhong(SurfaceOutput s, fixed3 lightDir, half3 viewDir, fixed atten){
	half3 h = normalize(lightDir + viewDir);
	fixed diff = max(0, dot(s.Normal, lightDir));
	float nh = max(0, dot(s.Normal, h));
	float spec = pow(nh, s.Specular * 128.0) * s.Gloss;

	fixed4 c;
	c.rgb = (s.Albedo * _LightColor0.rgb * diff + _LightColor0.rgb * _SpecColor.rgb * spec) * (atten * 2);
	c.a = s.Alpha + _LightColor0.a * _SpecColor.a * spec * atten;
	return c;
}