法线贴图 (Normal Map)

Graphics

解包NormalMap (Unpack NormalMap)


x向量存在a通道，y在g通道。而那种黄色的法线贴图是x在r通道，y在g通道，如果把b加上就会变成常见的蓝紫色Normal。

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//UnityStandardUtils.cginc中的解包方法
half3 UnpackScaleNormal(half4 packednormal, half bumpScale)
{
	#if defined(UNITY_NO_DXT5nm)
		return packednormal.xyz * 2 - 1;
	#else
		half3 normal;
		normal.xy = (packednormal.wy * 2 - 1);
		#if (SHADER_TARGET >= 30)
			// SM2.0: instruction count limitation
			// SM2.0: normal scaler is not supported
			normal.xy *= bumpScale;
		#endif
		normal.z = sqrt(1.0 - saturate(dot(normal.xy, normal.xy)));
		return normal;
	#endif
}
   
half3 unpackedNormal = UnpackScaleNormal(tex2D(_BumpMap, i.uv.xy), _Bumpness);

转换到世界空间去 (From Tangent Space to World Space)

转换到世界空间需要到对应点在世界的转换矩阵。

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tangentWorld = normalize(
	mul(_Object2World, half4(v.tangent.xyz, 0.0)).xyz);
   
normalWorld = normalize(
	mul(half4(v.normal, 0.0), _World2Object).xyz);
   
bitangentWorld = normalize(
	cross(o.normalWorld, o.tangentWorld)
	* v.tangent.w);
   
half3x3 local2WorldTranspose = half3x3(
					tangentWorld,
					bitangentWorld,
					normalWorld
					);

关于Normal, Tangent和Bitangent（Binormal）的解释：
Tangent space matrix (TBN)
What are normal, tangent and binormal vectors and how are they used.

最后获得世界空间的Normal

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half3 normalDir = normalize(mul(unpackedNormal, local2WorldTranspose));
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