一些光照模型

一些光照模型

1.  Lambert

Diffuse Light

与视角无关

float NdotL = max(0.0, dot(s.Normal, lightDir));

float4 finalColor;

finalColor.rgb = s.Albedo * _LightColor0 * NdotL;

finalColor.a = s.Alpha;

return finalColor;

 折叠源码

fixed diff = max(0, dot(s.Normal, lightDir));

 

fixed4 c;

c.rgb = s.Albedo * _LightColor0 * diff * atten;

c.a = s.Alpha;

return c;

2. Half-Lambert

半条命起源

可以看清物体暗的部分的形状，因此物体显得更加扁平

float NdotL = max(0.0, dot(s.Normal, lightDir));

float HalfLambertDiffuse = pow(NdotL * 0.5 + 0.5, 2.0);

float4 finalColor;

finalColor.rgb = s.Albedo * _LightColor0 * HalfLambertDiffuse * atten;

finalColor.a = s.Alpha;

return finalColor;

3. Phong

表现高光效果

diffuse light and specular light

float NdotL = max(0, dot(s.Normal, lightDir));

 

float3 lightReflectDirection = reflect(-lightDir, s.Normal);

float RdotV = max(0, dot(lightReflectDirection, viewDir));

float spec = pow(RdotV, _SpecPower/4) * _SpecularColor;

 

float4 color;

color.rgb = (s.Albedo * _LightColor0.rgb * NdotL) + (_LightColor0.rgb * _SpecularColor.rgb * spec) * atten;

color.a = s.Alpha;

return color;

4. Blinn-Phong

建立在Phong的基础上。Phong计算light reflection vector ，而Blinn计算Half Direction替之，即灯光方向和视角方向的半角向量。
好处是高光更加柔和。

float NdotL = max(0, dot(s.Normal, lightDir));

 

float3 halfVector = normalize(lightDir + viewDir);

float NdotH = max(0, dot(s.Normal, halfVector));

float spec = pow(NdotH, _SpecPower) * _SpecularColor;

 

float4 color;

color.rgb = (s.Albedo * _LightColor0.rgb * NdotL) + (_LightColor0.rgb * _SpecularColor.rgb * spec) * atten;

color.a = s.Alpha;

return color;

5. PBR

完全基于物理的

6. Banded-lighting

将连续的灯光变为离散的一段一段的

float NdotL = max(0.0, dot(s.Normal, lightDir));

 

float lightBandsMultiplier = _LightSteps / 256;

float lightBandsAdditive = _LightSteps / 2;

fixed bandedNdotL = (floor((NdotL * 256 + lightBandsAdditive) / _LightSteps))

    * lightBandsMultiplier;

 

float3 lightingModel = bandedNdotL * s.Albedo;

float3 attenColor = atten * _LightColor0.rgb;

float4 finalDiffuse = float4(lightingModel * attenColor, 1);

return finalDiffuse;

7. Minnaert

特别适合天鹅绒或月亮，这类多孔可渗透性或纤维状的表面，这类表面会导致大量光反向散射

float3 viewDirection = viewDir;

float NdotL = max(0, dot(s.Normal, lightDir));

float NdotV = max(0, dot(s.Normal, viewDirection));

 

float3 minnaert = saturate(NdotL * pow(NdotL*NdotV, _Roughness));

 

float3 lightingModel = minnaert * s.Albedo;

float3 attenColor = atten * _LightColor0.rgb;

float4 finalDiffuse = float4(lightingModel * attenColor, 1);

return finalDiffuse;

8. Oren–Nayar

Lambert 光照模型，是一个让光线向各个角度都均匀辐射的模型。这个均匀实在太不可思议了，真实物体表面理应不是这样的。

在灯光方向不变的情况下，观察物体的角度不同，物体表面光强、颜色也会发生变化（一般粗糙物体正光光强比背光光强要强）。就是光线向各个角度并非均匀辐射。

Oren-Nayar model 这个主要来自于Michael Oren和Shree K. Nayar在SIGGRAPH94上发表的论文Generalization of Lambert’s Reflectance Model。里面通过统计的等手段总结出比较接近真实粗糙表面的数学公式

http://www1.cs.columbia.edu/CAVE/publications/pdfs/Oren_SIGGRAPH94.pdf

float roughness = _Roughness;

float roughnessSqr = roughness * roughness;

float3 o_n_fraction = roughnessSqr / (roughnessSqr + float3(0.33, 0.13, 0.09));

float3 oren_nayar = float3(1, 0, 0) + float3(-0.5, 0.17, 0.45) * o_n_fraction;

float3 viewDirection = viewDir;

float cos_ndotl = saturate(dot(s.Normal, lightDir));

float cos_ndotv = saturate(dot(s.Normal, viewDirection));

float oren_nayar_s = saturate(dot(lightDir, viewDirection)) - cos_ndotl * cos_ndotv;

oren_nayar_s /= lerp(max(cos_ndotl, cos_ndotv), 1, step(oren_nayar_s, 0));

 

 

//lighting and final diffuse

float attenuation = atten;

float3 lightingModel = s.Albedo * cos_ndotl * (oren_nayar.x + s.Albedo * oren_nayar.y + oren_nayar.z * oren_nayar_s);

float3 attenColor = attenuation * _LightColor0.rgb;

float4 finalDiffuse = float4(lightingModel * attenColor, 1);

return finalDiffuse;