Atmospheric Scattering (Sean O'Neill - GPU Gems2)

float fInnerRadius = 10.0f;float fOuterRadius = 10.25f;   float fScale = 1 / (fOuterRadius - fInnerRadius);float fScaleDepth = 0.0125f;            //0.25f;//(fOuterRadius - fInnerRadius) / 2.0f;float fScaleOverScaleDepth = 16.0f;     //fScale / fScaleDepth;//      float fScaleOverScaleDepth = fScale / fScaleDepth;float fRayMult = 0.002f;float fMieMult = 0.0015f;float fkr4PI = fRayMult * 4.0f * (float)Math.PI;float fkm4PI = fMieMult * 4.0f * (float)Math.PI;float fKrESun = fRayMult * sun.GetIntensity();float fKmESun = fMieMult * sun.GetIntensity();float g = -0.991f;//      float fSkydomeRadius = 1500;float fSkydomeRadius = (6.378e6f) + 200000;int iNumSamples = 4;Vector3 vecCamera = camera.Position;vecCamera /= fSkydomeRadius;vecCamera.Y += fInnerRadius;vecCamera.X = 0;vecCamera.Z = 0;

float4x4 WorldViewProj;float3 v3LightDir;		// Light directionfloat3 v3CameraPos;		// Camera's current positionfloat3 v3InvWavelength;	// 1 / pow(wavelength, 4) for RGB channelsfloat fCameraHeight;float fCameraHeight2;float fInnerRadius;float fInnerRadius2;float fOuterRadius;float fOuterRadius2;// Scattering parametersfloat KrESun;			// Kr * ESunfloat KmESun;			// Km * ESunfloat Kr4PI;			// Kr * 4 * PIfloat Km4PI;			// Km * 4 * PI// Phase functionfloat g;float g2;float fScale;			// 1 / (outerRadius - innerRadius) = 4 herefloat fScaleDepth;		// Where the average atmosphere density is foundfloat fScaleOverScaleDepth;	// scale / scaleDepthfloat fSkydomeRadius;	// Skydome radius (allows us to normalize skydome distances etc)float fExposure;	// Exposure parameter for pixel shaderint numSamples;float samples;// Application to vertex structurestruct a2v{	float4 Position : POSITION0;};// Vertex to pixel shader structurestruct v2p{	float4 Position			: POSITION0;	float3 Direction		: TEXCOORD0;	float4 RayleighColor    : TEXCOORD1;	float4 MieColor			: TEXCOORD2;	//float4 RayleighColor	: COLOR;	//float4 MieColor		: COLOR;	};float scale(float cos){	float x = 1.0 - cos;	return fScaleDepth * exp(-0.00287 + x*(0.459 + x*(3.83 + x*(-6.80 + x*5.25))));}void RenderSkyVS(in a2v IN, out v2p OUT){	// Transform to clipspace	OUT.Position = mul(IN.Position, WorldViewProj);		// Get the ray from the camera to the vertex, and it's length (far point)	float3 v3Pos = IN.Position / fSkydomeRadius;	//v3Pos.y += 1;	v3Pos.y += fInnerRadius;	float3 v3Ray = v3Pos - v3CameraPos;	float fFar = length(v3Ray);	v3Ray /= fFar;		// Calculate the ray's starting position, then calculate its scattering offset	float3 v3Start = v3CameraPos;	float fHeight = length(v3Start);	float fDepth = exp(fScaleOverScaleDepth * (fInnerRadius - fCameraHeight));	float fStartAngle = dot(v3Ray, v3Start) / fHeight;	float fStartOffset = fDepth * scale(fStartAngle);				// Init loop variables	float fSampleLength = fFar / samples;	float fScaledLength = fSampleLength * fScale;	float3 v3SampleRay = v3Ray * fSampleLength;	float3 v3SamplePoint = v3Start + v3SampleRay * 0.5f;		// Loop the ray	float3 color;	for (int i = 0; i < numSamples; i++)	{		float fHeight = length(v3SamplePoint);		float fDepth = exp(fScaleOverScaleDepth * (fInnerRadius-fHeight));				float fLightAngle = dot(v3LightDir, v3SamplePoint) / fHeight;		float fCameraAngle = dot(v3Ray, v3SamplePoint) / fHeight;				float fScatter = (fStartOffset + fDepth*(scale(fLightAngle) - scale(fCameraAngle)));		float3 v3Attenuate = exp(-fScatter * (v3InvWavelength * Kr4PI + Km4PI));				// Accumulate color		v3Attenuate *= (fDepth * fScaledLength);		color += v3Attenuate;				// Next sample point		v3SamplePoint += v3SampleRay;	}		// Finally, scale the Mie and Rayleigh colors	OUT.RayleighColor.xyz = color * (v3InvWavelength * KrESun);	OUT.RayleighColor.w = 1.0f;	OUT.MieColor.xyz = color * KmESun;	OUT.MieColor.w = 1.0f;	OUT.Direction = v3CameraPos - v3Pos;}float4 RenderSkyPS(in v2p IN) : COLOR0{	float cos = dot(v3LightDir, IN.Direction) / length(IN.Direction);		//float rayleighPhase = 0.75 * (1.0 + cos*cos);	float rayleighPhase = 0.75 * (2.0 + 0.5 * cos*cos);		float miePhase = 1.5f * ((1.0f - g2) / (2.0f + g2)) *					 (1.0f + cos*cos) / pow(1.0f + g2 - 2.0f * g * cos, 1.5f);	// exposure => 1.0 - exp(-fExposure * color)	return 1 - exp(-fExposure * (rayleighPhase * IN.RayleighColor + miePhase * IN.MieColor));}technique RenderSky{	pass p0	{			VertexShader = compile vs_2_0 RenderSkyVS();		PixelShader = compile ps_2_0 RenderSkyPS();		ZWriteEnable = 0;	}	}

D3DXVECTOR4 vecCamera = *objRenderer->GetCameraPos();	D3DXMATRIX matWVP;	D3DXMatrixTranslation(&matWVP, -vecCamera.x, 0, -vecCamera.z);	D3DXMatrixMultiply(&matWVP, &matWVP, objRenderer->GetViewMatrix());	D3DXMatrixMultiply(&matWVP, &matWVP, objRenderer->GetProjectionMatrix());	// Scattering Sky Parameters	D3DXVECTOR4 vSunDir = m_pAtmosphere->GetDirection();	D3DXVECTOR4 vSunColourIntensity = m_pAtmosphere->GetColorAndIntensity();	float fInnerRadius = m_pAtmosphere->GetInnerRadius();	float fOuterRadius = m_pAtmosphere->GetOuterRadius();	float fScale = m_pAtmosphere->GetScale();	float fScaleDepth = m_pAtmosphere->GetScaleDepth();	float fScaleOverScaleDepth = m_pAtmosphere->GetScaleOverScaleDepth();	float g = m_pAtmosphere->GetHeyseyG();	float fkr4PI = m_pAtmosphere->GetKr4PI();	float fkm4PI = m_pAtmosphere->GetKm4PI();	float fKrESun = m_pAtmosphere->GetKrEsun();	float fKmESun = m_pAtmosphere->GetKmEsun();		vecCamera.x = 0;	vecCamera.z = 0;	vecCamera.y /= fSkydomeRadius;		// Set to unit scale	vecCamera.y *= fInnerRadius;		// Set to scale being used	vecCamera.y += fInnerRadius;		// Scale based on the actual Inner Radius of Earth	pSkydomeScatterFX->SetMatrix(m_pWorldViewProj, &matWVP);	pSkydomeScatterFX->SetVector(m_pv3LightDir, &vSunDir);	pSkydomeScatterFX->SetVector(m_pv3CameraPos, &vecCamera);	pSkydomeScatterFX->SetVector(m_pv3InvWavelength, m_pAtmosphere->GetInvWavelength());	pSkydomeScatterFX->SetFloat(m_pfCameraHeight,vecCamera.y);	pSkydomeScatterFX->SetFloat(m_pfCameraHeight2,vecCamera.y*vecCamera.y);	pSkydomeScatterFX->SetFloat(m_pfInnerRadius, fInnerRadius);	pSkydomeScatterFX->SetFloat(m_pfInnerRadius2, fInnerRadius * fInnerRadius);	pSkydomeScatterFX->SetFloat(m_pfOuterRadius, fOuterRadius);	pSkydomeScatterFX->SetFloat(m_pfOuterRadius2, fOuterRadius * fOuterRadius);	pSkydomeScatterFX->SetFloat(m_pKrESun,fKrESun);	pSkydomeScatterFX->SetFloat(m_pKmESun,fKmESun);	pSkydomeScatterFX->SetFloat(m_pKr4PI, fkr4PI);	pSkydomeScatterFX->SetFloat(m_pKm4PI, fkm4PI);	pSkydomeScatterFX->SetFloat(m_pg, g);	pSkydomeScatterFX->SetFloat(m_pg2, g*g);	pSkydomeScatterFX->SetFloat(m_pfScale, fScale);	pSkydomeScatterFX->SetFloat(m_pScaleDepth, fScaleDepth);	pSkydomeScatterFX->SetFloat(m_pScaleOverScaleDepth, fScaleOverScaleDepth);	pSkydomeScatterFX->SetFloat(m_pfSkydomeRadius, fSkydomeRadius);	pSkydomeScatterFX->SetInt(m_pnumSamples, iNumSamples);	pSkydomeScatterFX->SetInt(m_psamples, iNumSamples);	pSkydomeScatterFX->SetFloat(m_pfExposure, fExposure);

if (FAILED(objRenderer->GetD3Device()->CreateVertexDeclaration(skydomevertex_decl, &objSkydomeVertexDecl)))		return ;	void *ptrD3DBuffer;	// Marco - skydome generator that only creates what is necessary	// Radius = PlanetRadius + 200000	// Y offset is PlanetRadius	// Don't need anything below the horizon (i.e. Y < 0)	int nRings = 160;	int nSegments = 20;	// set vertex count and index count 	DWORD dwVertices = ( nRings + 1 ) * ( nSegments + 1 ) ;	DWORD dwIndices = 2 * nRings * ( nSegments + 1 ) ;	// Create the vertex buffer	if (FAILED(objRenderer->GetD3Device()->CreateVertexBuffer(iVertSize * dwVertices,		D3DUSAGE_WRITEONLY, 0, D3DPOOL_MANAGED , &l_pSkydomeVertices, NULL)))	{		return;	}	// Create the index buffer	if (FAILED(objRenderer->GetD3Device()->CreateIndexBuffer(dwIndices * sizeof(WORD),		0, D3DFMT_INDEX16, D3DPOOL_MANAGED, &l_pSkydomeIndices, NULL)))	{		return;	}	// Lock the vertex buffer	if (FAILED(l_pSkydomeVertices->Lock(0, 0, &ptrD3DBuffer, 0)))	{		return;	}	VertexSkydome* pVertex= (VertexSkydome*)ptrD3DBuffer;	// lock the index buffer 	if (FAILED(l_pSkydomeIndices->Lock(0, 0, &ptrD3DBuffer, 0)))		return;	WORD * pIndices = (WORD*)ptrD3DBuffer;	// Establish constants used in sphere generation		float fDeltaRingAngle = ( D3DX_PI / nRings );	float fDeltaSegAngle = ( 2.0f * D3DX_PI / nSegments );	WORD wVerticeIndex = 0 ; 	// Generate the group of rings for the sphere	for( int ring = 0; ring < nRings + 1 ; ring++ )	{		float r0 = sinf ( ring * fDeltaRingAngle );		float y0 = cosf ( ring * fDeltaRingAngle );		// Generate the group of segments for the current ring		for( int seg = 0; seg < nSegments + 1 ; seg++ )		{			float x0 = r0 * sinf( seg * fDeltaSegAngle );			float z0 = r0 * cosf( seg * fDeltaSegAngle );			// Add one vertices to the strip which makes up the sphere			pVertex->posX = x0 * fSkydomeRadius;			pVertex->posY = y0 * fSkydomeRadius - fSkydomeYAdjust;			pVertex->posZ = z0 * fSkydomeRadius;			pVertex ++;			// add two indices except for last ring 			if ( ring != nRings ) 			{				* pIndices = wVerticeIndex + ( WORD ) ( nSegments + 1 ) ; 				pIndices ++ ;				* pIndices = wVerticeIndex ; 				pIndices ++ ;				wVerticeIndex ++ ; 			} ; 		} ; // end for seg 	} // end for ring 	iNumSkydomeVerts = dwVertices;	l_pSkydomeVertices->Unlock();	iSkydomePrimitives = wVerticeIndex / 2;	l_pSkydomeIndices->Unlock();