c – HLSL法线映射矩阵乘法

(顶点着色器)：

float4x4 gWorldMatrix;
float4x4 gWorldViewProjectionMatrix;

float4 gWorldLightPosition;
float4 gWorldCameraPosition;

struct VS_INPUT 
{
   float4 mPosition : POSITION;
   float3 mNormal: NORMAL;
   float3 mTangent: TANGENT;
   float3 mBinormal: BINORMAL;
   float2 mUV: TEXCOORD0;
};

struct VS_OUTPUT 
{
   float4 mPosition : POSITION;
   float2 mUV: TEXCOORD0;
   float3 mLightDir: TEXCOORD1;
   float3 mViewDir: TEXCOORD2;
   float3 T: TEXCOORD3;
   float3 B: TEXCOORD4;
   float3 N: TEXCOORD5;
};

VS_OUTPUT vs_main( VS_INPUT Input )
{
   VS_OUTPUT Output;

   Output.mPosition = mul( Input.mPosition,gWorldViewProjectionMatrix );

   Output.mUV = Input.mUV;

   float4 worldPosition = mul( Input.mPosition,gWorldMatrix );

   float3 lightDir = worldPosition.xyz - gWorldLightPosition.xyz;
   Output.mLightDir = normalize( lightDir );

   float3 viewDir = normalize( worldPosition.xyz - gWorldCameraPosition.xyz );
   Output.mViewDir = viewDir;

   //object space=>world space
   float3 worldNormal = mul( Input.mNormal,(float3x3)gWorldMatrix );
   Output.N = normalize( worldNormal );

   float3 worldTangent = mul( Input.mTangent,(float3x3)gWorldMatrix );
   Output.T = normalize( worldTangent );

   float3 worldBinormal = mul( Input.mBinormal,(float3x3)gWorldMatrix );
   Output.B = normalize( worldBinormal);

   return Output;
}

(Pixel Shader)

struct PS_INPUT
{
   float2 mUV : TEXCOORD0;
   float3 mLightDir: TEXCOORD1;
   float3 mViewDir: TEXCOORD2;
   float3 T: TEXCOORD3;
   float3 B: TEXCOORD4;
   float3 N: TEXCOORD5;
};

sampler2D DiffuseSampler;
sampler2D SpecularSampler;
sampler2D NormalSampler;

float3 gLightColor;

float4 ps_main(PS_INPUT Input) : COLOR
{
   //read normal from tex
   float3 tangentNormal = tex2D( NormalSampler,Input.mUV ).xyz;
   tangentNormal = normalize( tangentNormal * 2 - 1 ); //convert 0~1 to -1~+1.

   //read from vertex shader
   float3x3 TBN = float3x3( normalize(Input.T),normalize(Input.B),normalize(Input.N) ); //transforms world=>tangent space

   TBN = transpose( TBN ); //transform tangent space=>world

   float3 worldNormal = mul( TBN,tangentNormal ); //note: mat * scalar
   //(since TBN is row matrix)

   float3 lightDir = normalize( Input.mLightDir ); 
   float3 diffuse = saturate( dot(worldNormal,-lightDir) );

   float4 albedo = tex2D( DiffuseSampler,Input.mUV );
   diffuse = gLightColor * albedo.rgb * diffuse;

   float3 specular = 0;
   if ( diffuse.x > 0 )
   {
      float3 reflection = reflect( lightDir,worldNormal );
      float3 viewDir = normalize( Input.mViewDir );

      specular = saturate( dot(reflection,-viewDir) );
      specular = pow( specular,20.0f );

      //further adjustments to specular (since texture is 2D)
      float specularIntensity = tex2D( SpecularSampler,Input.mUV );
      specular *= specularIntensity * gLightColor;
   }

   float3 ambient = float3(0.1f,0.1f,0.1f) * albedo;

   return float4(ambient + diffuse + specular,1);
}

代码有效,但我不太明白为什么我需要这样做

TBN =转置(TBN);在像素着色器中.

我通过顶点着色器的TBN值是那些在世界空间中的值(因此为什么我乘以gWorldMatrix),但我被告知

float3x3 TBN = float3x3(normalize(Input.T),
normalize(Input.N));

转换world =>切线(曲面)空间.

为什么是这样？