Unity Shader 之 不锈钢（各向异性材质）

Unity Shader 之 不锈钢（各向异性材质）

常见的实现方案

• 思路：
  先求出半角向量halfVector
  再求法线方向与光照方向的点积NdotL
  半角向量与各向异性方向点积HdotA
  求出各向异性：
  sin(（半角向量与各向异性方向点积+偏移值）的弧度值 * 180)
  再根据各向异性求出反光强度spec
  最后与光照颜色等进行整合

• 主要代码：

  inline fixed4 LightingAnisotropic (SurfaceAnisoOutput s, fixed3 lightDir, half3 viewDir, fixed atten)  
  {  
      fixed3 halfVector = normalize(normalize(lightDir) + normalize(viewDir));//normalize()函数把向量转化成单位向量  
  
      float NdotL = saturate(dot(s.Normal, lightDir));  
  
      fixed HdotA = dot(normalize(s.Normal + s.AnisoDirection), halfVector);  
      float aniso = max(0, sin(radians((HdotA + _AnisoOffset) * 180f)));//radians()函数将角度值转换为弧度值   
  
      float spec = saturate(pow(aniso, s.Gloss * 128) * s.Specular);//saturate(x）函数   如果x小于0返回 0;如果x大于1返回1;否则返回x;把x限制在0-1  
  
  
      fixed4 c;  
      c.rgb = ((s.Albedo * _LightColor0.rgb * NdotL) + (_LightColor0.rgb * _SpecularColor.rgb * spec)) * (atten * 2);  
      c.a = 1.0;  
      return c;  
  
  }

• 效果图：
  

参考链接：http://blog.youkuaiyun.com/wolf96/article/details/41843973

本文的实现方案

• 公式：公式采用的是Ward 92年在 Measuring and modeling anisotropic reflection中提出的。
  各项异性材质是BRDF的一部分， 有关BRDF的论文很多， 这里推荐一篇Physically-Based Shading at Disney by Brent Burley, Walt Disney Animation Studios [Revised Aug 31, 2012. Corrected normalization factor in Equation 4.]， 在这篇论文中还讲到了关于各项异性的几篇文章包括Walter在2005年在 Notes on the Ward BRDF中提出了对Ward各项异性材质公式的一些优化算法， 以及Pacanowski在2012年在Oliver Salazar Celis中提出的关于各项异性材质的新的公式。 有兴趣的童鞋可以试试。

• 本文中用到的贴图
  
  

• Shader中的主要代码

float _Diffuse, _Specular;
float _Gloss;
float _AnisoX, _AnisoY, _AnisoAngle, _AnisoIntensity;
sampler2D _AnisoTexture; float4 _AnisoTexture_ST;

struct v2f
{
    float4 pos : SV_POSITION;
    float3 normal : NORMAL;
    float4 tangent : TANGENT;
    float4 worldPos : TEXCOORD0;
    float2 texcoord : TEXCOORD1;
    LIGHTING_COORDS(3, 4)
};

void vert(in appdata_tan v, out v2f output)
{
    output.pos = UnityObjectToClipPos(v.vertex);
    output.normal = v.normal;
    output.tangent = v.tangent;
    output.worldPos = mul(unity_ObjectToWorld, v.vertex);
    output.worldPos /= output.worldPos.w;
    output.texcoord = v.texcoord;
    TRANSFER_VERTEX_TO_FRAGMENT(output);
}

void frag(in v2f input, out float4 c : COLOR)
{
    c.rgb = 0;



    float3 lightColor = _LightColor0.rgb;
    float3 vertPos = input.worldPos.xyz;
    float3 lightPos = _WorldSpaceLightPos0.xyz;
    float3 normalDir = normalize(UnityObjectToWorldNormal(input.normal));
    float3 tangentDir = normalize(UnityObjectToWorldNormal(input.tangent));
    float3 bitangentDir = normalize(cross(tangentDir, normalDir));
    float3 anisoDir = normalize(UnpackNormal(tex2D(_AnisoTexture, input.texcoord)));
    float3 lightDir = lightPos - vertPos;
    if (_WorldSpaceLightPos0.w<0.001) lightDir = lightPos;
    float3 b = bitangentDir;
    float3 t = tangentDir;
    float3 n = normalDir;
    //if (anisoDir.z<0.99)
    {
        float Pi = 3.141592654;
        float3 anisoParam = tex2D(_AnisoTexture, TRANSFORM_TEX(input.texcoord, _AnisoTexture));
        _AnisoX = anisoParam.r;
        _AnisoY = anisoParam.g;
        _AnisoAngle = anisoParam.b * 180;

        //t = normalize(anisoDir.x * tangentDir + anisoDir.y * bitangentDir);
        t = t * cos(_AnisoAngle*Pi/180) + b * sin(_AnisoAngle*Pi/180);
        n = normalDir;
        b = normalize(cross(t,n));
    }
    float3 l = normalize(lightDir);
    float3 v = normalize(_WorldSpaceCameraPos.xyz - vertPos);               
    float3 h = normalize(l+v);              
    float3 dotLN = saturate(dot(l,n));
    float3 dotHN = saturate(dot(h,n));
    float3 dotHT = (dot(h,t));
    float3 dotHB = (dot(h,b));
    float3 dotVN = max(0.01,dot(v,n));

    // attenuate
    float attenuation = LIGHT_ATTENUATION(input);

    // diffuse
    float3 diffuse = dotLN * lightColor * _Diffuse;

    // specular
    float3 specular = pow(dotHN, _Gloss*256) * _Specular * lightColor;
    specular = _Specular * lightColor *  sqrt(dotLN/dotVN) * exp(-2 * (dotHT*dotHT/_AnisoX/_AnisoX + dotHB*dotHB/_AnisoY/_AnisoY)/(1+dotHN));

    // reflect 
    float3 rv = reflect(-v, n);
    rv -= t * dot(rv,t);
    float3 refl = 0;
    for (int i=0; i<0; i++) {
        float3 drv = rv + t*i*0.02;
        refl += UNITY_SAMPLE_TEXCUBE_LOD(unity_SpecCube0, drv, 0);
        drv = rv -t*i*0.02;
        refl += UNITY_SAMPLE_TEXCUBE_LOD(unity_SpecCube0, drv, 0);
    }
    refl /= 10;
    //refl =  UNITY_SAMPLE_TEXCUBE_LOD(unity_SpecCube0, reflect(-v, n), 0);

    //refl = UNITY_SAMPLE_TEXCUBE_LOD(unity_SpecCube0, rv, 0);


    c.rgb = attenuation * (diffuse + specular);
    #ifdef UNITY_PASS_FORWARDBASE
    c.rgb += refl*0.2;

    #endif
    //c.rgb = attenuation;
    //c.rgb = sqrt(dotLN/dotVN)/10;
    //c.rgb = 0;

    //c.rgb = specular;
    //c.rgb = 0;
    c.a = 0;
} 

• 效果图：
  
  
  

有需要完整工程的童鞋可以留言给我。