float r = 1.0f/650e-9f; //red - 650nm	float g = 1.0f/610e-9f; //green - 610nm	float b = 1.0f/475e-9f; //blue - 475nm	float r2 = r*r;	float g2 = g*g;	float b2 = b*b;	float r4 = r2*r2;	float g4 = g2*g2;	float b4 = b2*b2;		//calculate rayleigh scattering coefficient	//br = (8pi^3(n^2 - 1)^2)/(3Nw^4)	//n = refractive index of air	//N = molecular density	//w = wavelength of light	float n = 1.0002926f;	float N = 2.545e25f;	float temp = 8.0f*D3DX_PI*D3DX_PI*D3DX_PI/(3.0f*N);	float temp2 = (n*n - 1.0f)*(n*n - 1.0f);	m_rayleigh.x = temp*temp2*r4;	m_rayleigh.y = temp*temp2*g4;	m_rayleigh.z = temp*temp2*b4;	//calculate mie scattering coefficient	//bm = 0.424*c*pi*(4pi^2/w^2)*K	//c = (0.6544*T - 0.6510)*10^-16	//	T = turbidity	//w = wavelength of light	//K ~ 0.67 (varies with colour)	float T = 555e-9f;	float c = (0.6544f*T - 0.6510f)*1e-16f;	temp = 0.67f*0.424f*c*D3DX_PI;	m_mie.x = temp*(4.0f*D3DX_PI*D3DX_PI*r2);	m_mie.y = temp*(4.0f*D3DX_PI*D3DX_PI*g2);	m_mie.z = temp*(4.0f*D3DX_PI*D3DX_PI*b2);	//store henyey greenstein constants	//HG = (1 - g^2)/(4pi(1 + g^2 - 2g*cos(theta)^3/2)	//g = directionality constant	g = 0.55f;	m_hg.x = 1.0f - g*g;	m_hg.y = 1.0f + g*g;	m_hg.z = 2.0f*g;	m_hg.w = 4.0f*D3DX_PI;	//store scaled scattering coefficients for phase functions	m_rayleigh2 = m_rayleigh * 3.0f/(16.0f*D3DX_PI);	m_mie2 = m_mie/(4.0f*D3DX_PI);		//store constant in inscattering function	m_inscatter.x = 1.0f/(m_rayleigh.x + m_mie.x);	m_inscatter.y = 1.0f/(m_rayleigh.y + m_mie.y);	m_inscatter.z = 1.0f/(m_rayleigh.z + m_mie.z);

float4x4 world;float4x4 viewProj;float4 sun; //sunlight colour + intensityfloat3 lightDir; //sunlight directionfloat3 rayleigh; //rayleigh coefficientfloat3 rayleigh2; //rayleigh * phase coefficientfloat3 mie; //mie coefficientfloat3 mie2; //mie * phase coefficientfloat4 hg; //henyey greenstein phase function constantsfloat3 inscatter; //inscattering coefficientstruct vsin{    float3 pos : POSITION;    float3 norm: NORMAL;    float2 tex : TEXCOORD0; //optical depth in y};struct vsout {    float4 final : POSITION;    float4 colour : COLOR0;};void VS(in vsin input, out vsout output) {    //transform to world space    output.final = mul(float4(input.pos, 1.0), world);    //transform to homogenous view space    output.final = mul(output.final, viewProj);    //transform norm to world space    input.norm = mul(input.norm, (float3x3) world);    //calculate angle between view vector and sun direction    //viewer at centre of dome, so view vector = norm    float2 viewAngle;    viewAngle.x = dot(-lightDir, input.norm);    //calculate scaled viewing angle for rayleigh scattering function    //3/16pi * rayleigh * (2 + 0.5*cos2(theta))    viewAngle.y = 2.0 + 0.5*(viewAngle.x * viewAngle.x);    //calculate extinction terms    //1.0f - e^(-(rayleigh + mie) * ray length)    float3 extinction = 1.0 - exp((-rayleigh + mie)*input.tex.y);    //calculate henyey greenstein mie scattering approximation    //m = (1 - g^2)/(4pi(1 + g^2 + 2gcos(theta))^(3/2))    //hg = {1 - g^2, 1 + g^2, 2g, 4pi};    float temp = hg.x/(hg.w*pow(hg.y + hg.z*viewAngle.x, 1.5));    //calculate inscattering    //(r(theta) + m(theta))/(r + m)*sun*extinction;    float3 r = rayleigh2 * viewAngle.y;    float3 m = mie2 * temp;        float3 i = (r + m)*inscatter*sun.xyz*extinction;    i *= sun.w; //multiply by sun intensity    //output the final colour    float4 colour = {i.x, i.y, i.z, 1.0};    output.colour = colour;}struct psin {    float4 colour : COLOR0;};float4 PS(in psin input) : COLOR {    return input.colour;}technique sky {    pass P0 {        VertexShader = compile vs_2_0 VS();        PixelShader = compile ps_1_1 PS();    }}