Sub-surface scattering hack ( comments wanted! )

string description = "Subsurface Scattering Hack";//------------------------------------float4x4 worldViewProj : WorldViewProjection;float4x4 world   : World;float4x4 worldInverseTranspose : WorldInverseTranspose;float4x4 viewInverse : ViewInverse;float4 LightPosition1 : POSITION<	string Object = "PointLight";	string UIName =  "Light 1";	string Space = "World";> 	= {1403.0f, 1441.0f, 1690.0f, 0.0f};float3 specColor<	string UIWidget = "color";	string UIName = "Specular Color";> = {0.9f, 0.9f, 1.0f};float3 lightColor<	string UIWidget = "color";	string UIName = "Light Color";> = {1.0f, 1.0f, 1.0f};float materialThickness<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 1.0f;	float UIStep = 0.01f;	string UIName = "Material Thickness Factor";> 	= 0.6f;float rimScalar<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 1.0f;	float UIStep = 0.01f;	string UIName = "Rim Light Strength";> 	= 1.0f;float extinctionCoefficientRed<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 1.0f;	float UIStep = 0.01f;	string UIName = "Extinction Coefficient, Red";> 	= 0.80f;float extinctionCoefficientBlue<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 1.0f;	float UIStep = 0.01f;	string UIName = "Extinction Coefficient, Blue";> 	= 0.12f;float extinctionCoefficientGreen<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 1.0f;	float UIStep = 0.01f;	string UIName = "Extinction Coefficient, Green";> 	= 0.20f;float specularPower<	string UIWidget = "Slider";	float UIMin = 0.0f;	float UIMax = 100.0f;	float UIStep = 0.50f;	string UIName = "Blinn Specular Power";> = 1.0f;texture diffuseTex;texture thicknessTex;texture normalTex;sampler normalSampler = sampler_state{	texture		= <normalTex>;	MinFilter	=	point;	MagFilter	=	point;	MipFilter	=	point;	AddressU	=	CLAMP;	AddressV	=	CLAMP;};sampler2D diffuseSampler = sampler_state{	Texture		=	<diffuseTex>;	MinFilter	=	Linear;	MagFilter	=	Linear;	MipFilter	=	Linear;	AddressU	=	WRAP;	AddressV	=	WRAP;};sampler2D thicknessSampler = sampler_state{	Texture		=	<diffuseTex>;	MinFilter	=	Linear;	MagFilter	=	Linear;	MipFilter	=	Linear;	AddressU	=	WRAP;	AddressV	=	WRAP;};struct VSOut{	float4 position			:	POSITION;	float2 texCoord			:	TEXCOORD0;	float3 worldNormal		:	TEXCOORD1;	float3 eyeVec     		:	TEXCOORD2;	float3 lightVec			:	TEXCOORD3;	float3 worldTangent		: 	TEXCOORD4;	float3 worldBinormal		: 	TEXCOORD5;	float3 vertPos			:	TEXCOORD6;};struct AppData {   	float4 position	:	POSITION;	float2 UV	:	TEXCOORD0;	float3 normal	:	NORMAL;	float3 tangent	: 	TANGENT;	float3 binormal	: 	BINORMAL;};VSOut SkinVS(AppData IN, uniform float4 lightPosition){	VSOut OUT;	OUT.worldNormal = normalize(mul(IN.normal, worldInverseTranspose).xyz);	OUT.worldTangent = normalize(mul(IN.tangent, worldInverseTranspose).xyz);	OUT.worldBinormal = normalize(mul(IN.binormal, worldInverseTranspose).xyz);	 	float3 worldSpacePos = mul(IN.position, world);	OUT.lightVec = lightPosition - worldSpacePos;	OUT.texCoord = IN.UV;	OUT.eyeVec = viewInverse[3].xyz - worldSpacePos;	OUT.position = mul(IN.position, worldViewProj);	OUT.vertPos = worldSpacePos;	return OUT;};float halfLambert(float3 vec1, float3 vec2){	float product = dot(vec1, vec2);	product *= 0.5;	product += 0.5;	return product;}float blinnPhongSpecular(float3 normalVec, float3 lightVec, float specPower){	float3 halfAngle = normalize(normalVec + lightVec);	return pow(saturate(dot(normalVec, halfAngle)), specPower);}float4 SkinPS(VSOut IN) : COLOR0{	float attenuation = (1.0f/distance(LightPosition1, IN.vertPos));	attenuation *= 10.0f;	float3 eyeVec 	= normalize(IN.eyeVec);	float3 lightVec = normalize(IN.lightVec.xyz);	float3 worldNormal = normalize(IN.worldNormal);	//float3 nMap = tex2D(normalSampler, IN.texCoord);	//worldNormal.x = dot(nMap.x, IN.worldTangent);	//worldNormal.y = dot(nMap.y, IN.worldBinormal);	//worldNormal.z = dot(nMap.z, IN.worldNormal);	float4 dotLN	= halfLambert(lightVec, worldNormal) * attenuation;	float3 indirectLightComponent = (float3)(materialThickness * max(0, dot(-worldNormal, lightVec)));	indirectLightComponent += materialThickness * halfLambert(-eyeVec, lightVec);	indirectLightComponent *= attenuation;	indirectLightComponent.r *= extinctionCoefficientRed;	indirectLightComponent.g *= extinctionCoefficientGreen;	indirectLightComponent.b *= extinctionCoefficientBlue;	indirectLightComponent.rgb *= tex2D(thicknessSampler, IN.texCoord).r;	float3 rim = (float3)(1.0f - max(0.0f, dot(worldNormal, eyeVec)));	rim *= rim;	dotLN *= tex2D(diffuseSampler, IN.texCoord);	float4 finalCol = dotLN + float4(indirectLightComponent, 1.0f);	rim *= max(0.0f, dot(worldNormal, lightVec)) * specColor;	finalCol.rgb += (rim * rimScalar * attenuation * finalCol.a);	finalCol.rgb += (blinnPhongSpecular(worldNormal, lightVec, specularPower) * attenuation * specColor * finalCol.a * 0.05f);	finalCol.rgb *= lightColor;	return float4(finalCol);};technique subSurfaceScattering{    pass p0     {				VertexShader		= compile vs_2_0 SkinVS(LightPosition1);		PixelShader			= compile ps_2_0 SkinPS();		ZEnable 			= true;		ZWriteEnable 		= true;		AlphaBlendEnable	= false;		SrcBlend 			= SrcAlpha;		DestBlend 			= InvSrcAlpha;		CullMode 			= CW; //None, CW, or CCW    }}

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Original post by samoth Thanks for the shader code, InvalidPointer. Unluckily, it'll take some work this weekend to get it to work, since FX Composer doesn't like something, it crashes right away :( I've been thinking about thickness and all for a while, there seems to be no easy way to get it perfect everywhere. Even a thickness map won't do, because no matter how you turn it, the ears will always be shaded wrong. There's of course the option to calculate per-pixel thicknes like in nVidia's "Luna" demo, but then we're not talking about a fast and efficient implementation any more (render several passes, blur, etc...). Also, the algorithm again is only an approximation. Mostly it doesn't matter much, but for example looking at the oral cavity from the side, it will produce a false "thick" result, when in fact it's mostly "empty" air with two thin layers of cheeks. So, I was wondering if shadow mapping the skull wouldn't be helpful, and still cheap enough (a single z-only render of a possibly much simplified model). The idea is to scale the head model down a bit, and remove/flatten ears and nose and render that into the shadow map. It probably doesn't even have to be perfectly anatomically accurate. So that will leave you with an "outer part" where there is skin and flesh (and rim light scattering), and an "inner part" where bones absorb all of the back light (regardless of thickness), so only scattering from incidential light and half-lambert lighting account to the colour. Thickness should not be something to worry about much then. Around the border, anything N dot V isn't a terribly bad approximation, since the normals will point more "sidewards" the thinner the cross-section. Now, in the "deeper" regions it does not work so well, but we have these masked out with the shadow map. Also, the disturbing artefacts when the ear is rim-lit although it obviously couldn't be (as the head is in the way) are gone.