Direct3D 12——灯光——点光

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衰减

实现

//实现了一种线性衰减因子的计算方法，可将其应用于点光源于聚光灯 float CalcAttenuation(float d, float falloffStart, float falloffEnd) { 
    // Linear falloff. return saturate((falloffEnd-d) / (falloffEnd - falloffStart)); } //代替菲涅尔方程的石里克近似。此函数基于光向量L于表面法线n之间的夹角，并根据菲涅尔效应近似地计算出以n为法线的表面所反射光的百分比 // Schlick gives an approximation to Fresnel reflectance (see pg. 233 "Real-Time Rendering 3rd Ed."). // R0 = ( (n-1)/(n+1) )^2, where n is the index of refraction. float3 SchlickFresnel(float3 R0, float3 normal, float3 lightVec) { 
    float cosIncidentAngle = saturate(dot(normal, lightVec)); float f0 = 1.0f - cosIncidentAngle; float3 reflectPercent = R0 + (1.0f - R0)*(f0*f0*f0*f0*f0); return reflectPercent; } //计算反射到观察者眼中的光量，该值为漫反射光量于镜面反射光量的总和 float3 BlinnPhong(float3 lightStrength, float3 lightVec, float3 normal, float3 toEye, Material mat) { 
    //m由光泽度推导而来，而光泽度则根据粗糙度求得 const float m = mat.Shininess * 256.0f; float3 halfVec = normalize(toEye + lightVec); float roughnessFactor = (m + 8.0f)*pow(max(dot(halfVec, normal), 0.0f), m) / 8.0f; float3 fresnelFactor = SchlickFresnel(mat.FresnelR0, halfVec, lightVec); float3 specAlbedo = fresnelFactor*roughnessFactor; //尽管我们进行的是LDR（low dynamic range .低动态范围）渲染，但spec（镜面反射）公式得到 // 的结果仍会超出范围[0,1],因此现将其按比例缩小一些 // Our spec formula goes outside [0,1] range, but we are  // doing LDR rendering. So scale it down a bit. specAlbedo = specAlbedo / (specAlbedo + 1.0f); return (mat.DiffuseAlbedo.rgb + specAlbedo) * lightStrength; } //点光 float3 ComputePointLight(Light L, Material mat, float3 pos, float3 normal, float3 toEye) { 
    //自表面指向光源的向量  float3 lightVec = L.Position - pos; //由表面到光源的距离 float d = length(lightVec); //范围检测 if(d > L.FalloffEnd) return 0.0f; //对光向量进行规范化处理 lightVec /= d; //通过朗伯余弦定律按比例降低光强 // Scale light down by Lambert's cosine law. float ndotl = max(dot(lightVec, normal), 0.0f); float3 lightStrength = L.Strength * ndotl; //根据距离计算光的衰减  float att = CalcAttenuation(d, L.FalloffStart, L.FalloffEnd); lightStrength *= att; return BlinnPhong(lightStrength, lightVec, normal, toEye, mat); }