This document discusses wrapped diffuse shading. It is used in Team Fortress 2 to provide a more subtle reflectance by wrapping a hemisphere around the shading model. Wrapped diffuse is similar to half Lambert shading and is commonly used to represent subsurface scattering and particle lighting. The wrapped function uses half Lambert to sample values from a 1D wrapped diffuse texture. Team Fortress 2 implements this by precomputing lighting calculations in a texture to improve performance. Code examples are provided for specular fresnel, primary specularity, rim fresnel, upward ambient rim, and mixing the components for the final shading result.

1. Wrapped Diffuse
이민웅
Shader Study

2. Wrapped Diffuse
• 팀 포트리스 2에서 사용
• subsurface scattering, area light source,
더 부드러운 reflectance 를 표현하기 위해
서 Hemisphere(반구)를 감싸는 셰이딩 모
델
Lambert
Wrapped Diffuse

3. Wrapped Diffuse
• HarfLambert 공식과 비슷함
– W=1이면, Half Lambert 공식
• Half Lambert와 유사하게 투과되는 느낌을
표현하는데 많이 사용
– 피부, 나뭇잎, 파티클 라이팅에 주로 사용
기본 Lambert Diffuse 공식
float diffuse = max(0, dot(normal, lightdirection));
기본 HalfLambert Diffuse 공식
float halflambert_term = dot(normal, lightdirection) * 0.5f + 0.5f
Wrapped Diffuse 공식
float diffuse = saturate((dot(normal, lightdirection) + OFFSET) / (1.0+OFFSET ));

4. Wrapped Diffuse
Wrapped SH 자세한 내용
http://blog.selfshadow.com/2011/12/31/righting-wrap-part-1/
http://blog.selfshadow.com/2012/01/07/righting-wrap-part-2/
Wrap Shading
www.iro.umontreal.ca/~derek/files/jgt_wrap.pdf

5. Wrapped Diffuse
• 팀 포트리스 방식
– Wrapped Function은 Half Lambert를 이용해서,
1D Wrapped Diffuse Texture에서 값을 얻어오
는것
– GPU Gems 16. Real-Time Approximation to
Subsurface Scattering
• Wrap Lighting 계산 내용을 미리 Texture로 저장하
여 사용함

6. WarpTex
Lambert
Half Lambert
Warping Function
Squared Half Lambert (Not used)
illuminance( P, n, PI)
{
Ln = normalize(L);
halflambert += .5*(Ln.nf)+.5;
float chl = clamp(halflambert,0.01,1);
accumulateMapColor = texture(warp,chl,0)*2;
hlsw_clrlght += Cl*accumulateMapColor;
}
diffusecolor = albedocolor * (Ka + hlsw_clrlght);
Light Color
Ambient
Albedo
Ka : ambient
Cl : LightColor
http://www.sfdm.scad.edu/faculty/mkesson/vsfx419/wip/spring11/eric_kurzmack/toon.html

7. Specular Fresnel
Mixed Specular
Primary Specularity
Rim Fresnel
Upward Ambient Rim
Final Mix
http://www.sfdm.scad.edu/faculty/mkesson/vsfx419/wip/spring11/eric_kurzmack/toon.html
Rim Specular

8. Code
Specular Fresnel
vector i= normalize(-I);
float fres=spline((nf.i),1,1,1,.95,.6,.6);
Primary Specularity
illuminance( P, n, PI/2)
{
Ln = normalize(L);
vector R = reflect(-Ln,nf);
ridot += clamp(max(0,(R.i)),.01,.99);
phngspec += (1-fres)*pow(ridot,specE);
}
Mixed Specular
illuminance( P, n, PI/2)
{
Ln = normalize(L);
vector R = reflect(-Ln,nf);
vector R2 = reflect(Ln,nf);
ridot += clamp(max(0,(R.i)),.01,.99);
ridot2 += clamp(max(0,(R2.i)),.01,.99);
phngspec += (1-fres)*pow(ridot,specE);
phngrim += rimfres*pow(ridot2,Krim);
phngmix += Cl*Ks*(max(phngrim,phngspec)*2);
}
speccolor = phngmix;
Rim Fresnel
vector i= normalize(-I);
float rimfres=pow((1-(nf.i)),2);
vector i= normalize(-I);
Upward Ambient Rim
float upward = clamp((nf.vector(0,1,0)),0,1);
float uprim= upward*rimfres*Kr*(Ka*5);
Rim Specular
illuminance( P, n, PI/2)
{
Ln = normalize(L);
vector R2 = reflect(Ln,nf);
ridot2 += clamp(max(0,(R2.i)),.01,.99);
phngrim += rimfres*pow(ridot2,Krim);
}
Final Mix
Ci = Oi*(diffusecolor+speccolor+uprim);

9. Q&A

10. 참고자료
• Wrap Shading :
http://www.iro.umontreal.ca/~derek/publication8.html
• Energy-Conserving Wrapped Diffuse
• Wrapped Diffuse와 팀포트리스 셰이딩 :
http://cagetu.egloos.com/5621806
• 팀포트리스 셰이딩 따라해보기 :
http://cagetu.egloos.com/4212681
• Energy Conservation in Games :
http://www.rorydriscoll.com/2009/01/25/energyconservation-in-games/
• http://www.gamedevforever.com/150
• http://cagetu.egloos.com/5621806