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Migi0027

DX11 DX11 - Volume Rendering - Article Misunderstanding

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Migi0027    4628

Hi guys! Again... ohmy.png

 

So I'm trying to follow an article/tutorial on volume rendering from GraphicsRunner (Great!) [ http://graphicsrunner.blogspot.dk/2009/01/volume-rendering-101.html ].

 

But there is something which I don't understand, which is the following:

 

 

 

We could always calculate the intersection of the ray from the eye to the current pixel position with the cube by performing a ray-cube intersection in the shader. But a better and faster way to do this is to render the positions of the front and back facing triangles of the cube to textures. This easily gives us the starting and end positions of the ray, and in the shader we simply sample the textures to find the sampling ray.

 

So I understand that I have to render the back and front culled positions to individual textures, which I am doing and it works (It looks fine), but does he mean render the depth model into view + projected space, or to render it as a texture that can be sampled onto the cube with the cubes respective texture coordinates?

 

Thanks, as always.

-MIGI0027

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Jason Z    6434

I read that post a while back, and what he is doing is storing the end points of a segment that would be created by passing a ray through the volume, and then using those end points to do the ray marching through the volume.  So what you need to do is look at his comparison function and figure out how he performs the iterative step.

 

In my volume rendering implementation in Hieroglyph 3, I use the texture space coordinates and step through the texture that way.  If you wanted to do that, you would find the 3D texture coordinate at the pixel location for the front and back faces, and store them accordingly.  Then you can simply step from the front value to the back value and do a texture lookup at each step, looking for the intersection with the isosurface.

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Migi0027    4628

Still testing and changing.

 

If useful, here is the shader:

cbuffer ConstantObjectBuffer : register (b0)
{
	matrix worldMatrix;

	float3 StepSize;
	float Iterations;

	float4 ScaleFactor;
};

#define Side 2

cbuffer ConstantFrameBuffer : register (b1)
{
	
	matrix viewMatrix;
	matrix projectionMatrix;

	float3 eyepos;
	float cppad;

	float4 lightvec;
	float4 lightcol;

	float FogStart;
	float FogEnd;
	float2 __space;

	float3 FogColor;
	float shadows;

	float SpecularIntensity;
	float3 pad3;
	float4 SpecularColor;
}

//***************************************************//
//                 VERTEX SHADER                     //
//***************************************************//

struct VOut
{
    float4 position : SV_POSITION;
    float3 texC		: TEXCOORD0;
    float4 pos		: TEXCOORD1;
    float2 texcoord : TEXCOORD2;
    float3 normal   : NORM;
};

struct GlobalIn
{
	float4 position : POSITION;
	float4 normal : NORMAL;
	float2 texcoord : TEXCOORD;
	float4 tangent : TANGENT;
};
	
**CE_RESERVED_SHADER[INPUTS]**

Texture3D t_VolData : register(t0);
Texture2D t_TransFront : register(t1);
Texture2D t_TransBack : register(t2);

SamplerState ss;

VOut VShader(GlobalIn input)
{
    VOut output;

    input.position.w = 1.0f;
	output.texcoord = input.texcoord;

	// Calculate the position of the vertex against the world, view, and projection matrices.
    output.position = mul(input.position, worldMatrix);
    output.position = mul(output.position, viewMatrix);
    output.position = mul(output.position, projectionMatrix);

	output.texC = input.position;
    output.pos = output.position;
    output.normal = mul(float4(input.normal.xyz,0), worldMatrix);
	
    return output;
}

//***************************************************//
//                 PIXEL SHADER                      //
//***************************************************//

struct POut
{
	float4 Diffuse  : SV_Target0;
	float4 Position : SV_Target1;
	float4 Depth    : SV_Target2;
	float4 Normals  : SV_Target3;
	float4 Lighting : SV_Target4;
};

// Functions
float4 GetVRaycast(VOut input)
{
	//calculate projective texture coordinates
    //used to project the front and back position textures onto the cube
    float2 texC = input.pos.xy /= input.pos.w;
	texC.x =  0.5f*texC.x + 0.5f; 
	texC.y = -0.5f*texC.y + 0.5f;  
 
    float3 front = t_TransFront.Sample(ss, texC).xyz;
    float3 back = t_TransBack.Sample(ss, texC).xyz;
 
    float3 dir = normalize(back - front);
    float4 pos = float4(front, 0);
 
    float4 dst = float4(0, 0, 0, 0);
    float4 src = 0;
 
    float value = 0;
 
    float3 Step = dir * StepSize;
 
    for(int i = 0; i < 32; i++)
    {
        pos.w = 0;
        value = t_VolData.Sample(ss, pos).r;
             
        src = (float4)value;
        src.a *= .5f; //reduce the alpha to have a more transparent result 
         
        //Front to back blending
        // dst.rgb = dst.rgb + (1 - dst.a) * src.a * src.rgb
        // dst.a   = dst.a   + (1 - dst.a) * src.a     
        src.rgb *= src.a;
        dst = (1.0f - dst.a)*src + dst;     
     
        //break from the loop when alpha gets high enough
        if(dst.a >= .95f)
            break; 
     
        //advance the current position
        pos.xyz += Step;
     
        //break if the position is greater than <1, 1, 1>
        if(pos.x > 1.0f || pos.y > 1.0f || pos.z > 1.0f)
            break;
    }
 
    return dst;
}

POut PShader(VOut input)
{
	POut output;

	// Depth
	output.Depth = float4(0, 0, 0, 1.0f);

	// Normals
	output.Normals = float4(normalize(input.normal), 1);
	output.Position = float4(0, 0, 0, 1);
	output.Lighting = float4(1, 1, 1, 1);

	output.Diffuse = GetVRaycast(input);

	return output;
}

Thanks!

-MIGI0027

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Migi0027    4628

Can somebody confirm that this is an Ok way of loading a volume texture:

// Will be filled and returned
	ID3D11ShaderResourceView* pSRV = NULL;
 
	// Build the texture header descriptor
	D3D11_TEXTURE3D_DESC descTex;
	descTex.Width = width;
	descTex.Height = height;
	descTex.Depth = depth;
	descTex.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
	descTex.Usage = D3D11_USAGE_DEFAULT;
	descTex.BindFlags = D3D11_BIND_SHADER_RESOURCE | D3D11_BIND_RENDER_TARGET;
	descTex.CPUAccessFlags = 0;
	descTex.MipLevels = 1;
	descTex.MiscFlags = D3D10_RESOURCE_MISC_GENERATE_MIPS;

	// Load Data into Memory
	const int size = height*width*depth;

	// Initialize memory
    unsigned int* pVolume = new unsigned int[size];

	// Load into memory
	FILE* pFile = fopen ( (const char*)filePath.c_str() , (const char*)"rb" );
	fread(pVolume,sizeof(unsigned int), size, pFile);
    fclose(pFile);
 
	// Resource data descriptor, with depth
	D3D11_SUBRESOURCE_DATA data ;
	data.pSysMem = pVolume;
	data.SysMemPitch = 1.0f * width;
	data.SysMemSlicePitch = width * height * 1;

	/*_until(r, depth)
	{
		// Fetch Data

		memset( &data[r], 0, sizeof(D3D11_SUBRESOURCE_DATA));
		data[r].pSysMem = pData;
		data[r].SysMemPitch = 4 * width;
	}*/
 
	// Create the 3d texture from data
	ID3D11Texture3D * pTexture = NULL;
	HV( pDevice->CreateTexture3D( &descTex, &data, &pTexture ));
 
	// Create resource view descriptor
	D3D11_SHADER_RESOURCE_VIEW_DESC srvDesc;
	srvDesc.Format = descTex.Format;
	srvDesc.ViewDimension = D3D11_SRV_DIMENSION_TEXTURE3D;

	srvDesc.Texture3D.MostDetailedMip = 0;
	srvDesc.Texture3D.MipLevels = D3D11_RESOURCE_MISC_GENERATE_MIPS;

	// Create the shader resource view
	HV( pDevice->CreateShaderResourceView( pTexture, &srvDesc, &pSRV ));
 
	return pSRV;

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unbird    8335
One thing: Your pitches are wrong. For RGBA8 a texel is 4 bytes in size, so
data.SysMemPitch = width * 4;
data.SysMemSlicePitch = width * height * 4;
And the pitches are uints, not floats (the compiler likely warns you here).

I'm probably sounding like a broken record now but I recommend using PIX/graphics debugger to see if resources are loaded/initialized fine.

PS: Oh, and thanks for the first link. That's quite a resourceful site. And it's mostly C# biggrin.png

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Migi0027    4628

Ok, so I'm just going to post all the code in case that I did something stupid as usual. tongue.png

 

Back, Front map rendering:

cbuffer ConstantObjectBuffer : register (b0)
{
	matrix worldMatrix;

	float pad_f;
	float instance;
	float2 pad_v2;
};

cbuffer ConstantFrameBuffer : register (b1)
{
	matrix viewMatrix;
	matrix projectionMatrix;
};


struct VOut
{
    float4 position : SV_POSITION;
    float3 texC		: TEXCOORD0;
    float4 pos		: TEXCOORD1;
};

Texture2D t_alphamap : register(t0);
Texture2D t_dffalpha : register(t1);
SamplerState ss;

VOut VShader(float4 position : POSITION, float4 normal : NORMAL, float2 texcoord : TEXCOORD, float3 instancePosition : INSTANCEPOS)
{
    VOut output;

	if (instance == 1)
	{
		position.x += instancePosition.x;
		position.y += instancePosition.y;
		position.z += instancePosition.z;
	}

    position.w = 1.0f;
	position = position * float4(1, 1, 1, 1);

	// Calculate the position of the vertex against the world, view, and projection matrices.
    output.position = mul(position, worldMatrix);
    output.position = mul(output.position, viewMatrix);
    output.position = mul(output.position, projectionMatrix);

	output.texC = position;
    output.pos = output.position;

    return output;
}

float4 PShader(VOut input) : SV_TARGET
{
	return float4(input.texC, 1.0f);
}

Code for volume rendering:

//*******CONFIGURE OBJECT BUFFER
	bff_PrObject.worldMatrix = world;
	bff_PrObject.Iterations = 24;

	//*******CALCULATE PROPERTIES

	float mStepScale = 1.0f;

	float maxSize = (float)max(volume->m_pVolumeData.m_Width, max(volume->m_pVolumeData.m_Height, volume->m_pVolumeData.m_Depth));
	bff_PrObject.StepSize = D3DXVECTOR3(1.0f / volume->m_pVolumeData.m_Width, 1.0f / volume->m_pVolumeData.m_Height, 1.0f / volume->m_pVolumeData.m_Depth);
	bff_PrObject.Iterations = (int)maxSize * (1.0f / mStepScale);

	D3DXVECTOR3 sizes = D3DXVECTOR3(volume->m_pVolumeData.m_Width, volume->m_pVolumeData.m_Height, volume->m_pVolumeData.m_Depth);
	D3DXVECTOR3 ratios = D3DXVECTOR3(1, 1, 1);

	D3DXVECTOR3 r(sizes.x * ratios.x, sizes.y * ratios.y, sizes.z * ratios.z);
	
	D3DXVECTOR3 c1 = (D3DXVECTOR3(1, 1, 1) * maxSize);
	D3DXVECTOR3 d(c1.x / r.x, c1.y / r.y, c1.z / r.z);

	bff_PrObject.ScaleFactor = D3DXVECTOR4( 1.0f / d.x, 1.0f / d.y, 1.0f / d.z, 1.0f );

	//*******SMART SEND ALL BUFFERS
	devcon->UpdateSubresource(pCBuffer[0], 0, 0, &bff_PrObject, NULL, NULL);
	devcon->UpdateSubresource(pCBuffer[1], 0, 0, &bff_PrFrame, NULL, NULL);

	devcon->VSSetConstantBuffers(0, 2, pCBuffer);
	devcon->PSSetConstantBuffers(0, 2, pCBuffer);

	//*******SEND RESOURCES
	ID3D11ShaderResourceView 
		*front = volume->transHolder.m_pFront.GetShaderResourceView(), 
		*back = volume->transHolder.m_pBack.GetShaderResourceView();

	devcon->PSSetShaderResources(0, 1, &volume->m_pVolumeData.pTexture);
	devcon->PSSetShaderResources(1, 1, &front);
	devcon->PSSetShaderResources(2, 1, &back);

	FOREACH (volume->Parameters.Parameters.size())
	{
		devcon->PSSetShaderResources(volume->Parameters.Parameters[i].slot, 1, &volume->Parameters.Parameters[i].resource);
	}

	//*******PREPARE PASS
	Pass.Prepare(devcon, rastManager);

	devcon->DrawIndexed(bf.IndexCount, 0, 0);

	//*******CLEAN UP
	ID3D11ShaderResourceView *n = NULL;
	FOREACH (volume->Parameters.Parameters.size())
	{
		devcon->PSSetShaderResources(volume->Parameters.Parameters[i].slot, 1, &n);
	}
	
	devcon->PSSetShaderResources(0, 1, &n);
	devcon->DSSetShaderResources(1, 1, &n);
	devcon->DSSetShaderResources(2, 1, &n);

Shader code for volume:

cbuffer ConstantObjectBuffer : register (b0)
{
	matrix worldMatrix;

	float3 StepSize;
	float Iterations;

	float4 ScaleFactor;
};

#define Side 2

cbuffer ConstantFrameBuffer : register (b1)
{
	
	matrix viewMatrix;
	matrix projectionMatrix;

	float3 eyepos;
	float cppad;

	float4 lightvec;
	float4 lightcol;

	float FogStart;
	float FogEnd;
	float2 __space;

	float3 FogColor;
	float shadows;

	float SpecularIntensity;
	float3 pad3;
	float4 SpecularColor;
}

//***************************************************//
//                 VERTEX SHADER                     //
//***************************************************//

struct VOut
{
    float4 position : SV_POSITION;
	float3 texC		: TEXCOORD0;
    float4 pos		: TEXCOORD1;
	float2 texcoord : TEXCOORD2;
	float3 normal   : NORM;

	**CE_RESERVED_SHADER[LINKAGE]**
};

struct GlobalIn
{
	float4 position : POSITION;
	float4 normal : NORMAL;
	float2 texcoord : TEXCOORD;
	float4 tangent : TANGENT;
};
	
**CE_RESERVED_SHADER[INPUTS]**

Texture3D t_VolData : register(t0);
Texture2D t_TransFront : register(t1);
Texture2D t_TransBack : register(t2);

sampler3D VolumeS = sampler_state
{
	Texture = <t_VolData>;
	MinFilter = LINEAR;
	MagFilter = LINEAR;
	MipFilter = LINEAR;
	
	AddressU = Border;				// border sampling in U
    AddressV = Border;				// border sampling in V
    AddressW = Border;
    BorderColor = float4(0,0,0,0);	// outside of border should be black
};

SamplerState ss;

VOut VShader(GlobalIn input)
{
    VOut output;

    input.position.w = 1.0f;
	output.texcoord = input.texcoord;

	**CE_RESERVED_SHADER[PREVERTEX]**

	// Calculate the position of the vertex against the world, view, and projection matrices.
    output.position = mul(input.position, worldMatrix);
    output.position = mul(output.position, viewMatrix);
    output.position = mul(output.position, projectionMatrix);

	output.texC = input.position;
    output.pos = output.position;
    output.normal = mul(float4(input.normal.xyz,0), worldMatrix);

	**CE_RESERVED_SHADER[VERTEX]**
	
    return output;
}

//***************************************************//
//                 PIXEL SHADER                      //
//***************************************************//

struct POut
{
	float4 Diffuse  : SV_Target0;
	float4 Position : SV_Target1;
	float4 Depth    : SV_Target2;
	float4 Normals  : SV_Target3;
	float4 Lighting : SV_Target4;
};

// Functions
float4 GetVRaycast(VOut input)
{
	//calculate projective texture coordinates
    //used to project the front and back position textures onto the cube
    float2 texC = input.pos.xy /= input.pos.w;
	texC.x =  0.5f*texC.x + 0.5f; 
	texC.y = -0.5f*texC.y + 0.5f;  
 
    float3 front = t_TransFront.Sample(ss, texC).xyz;
    float3 back = t_TransBack.Sample(ss, texC).xyz;
 
    float3 dir = normalize(back - front);
    float4 pos = float4(front, 0);
 
    float4 dst = float4(0, 0, 0, 0);
    float4 src = 0;
 
    float value = 0;
 
    float3 Step = dir * StepSize;
 
    for(int i = 0; i < 32; i++)
    {
        pos.w = 0;
        value = t_VolData.Sample(ss, pos).r;
             
        src = (float4)value;
        src.a *= .5f; //reduce the alpha to have a more transparent result 
         
        //Front to back blending
        // dst.rgb = dst.rgb + (1 - dst.a) * src.a * src.rgb
        // dst.a   = dst.a   + (1 - dst.a) * src.a     
        src.rgb *= src.a;
        dst = (1.0f - dst.a)*src + dst;     
     
        //break from the loop when alpha gets high enough
        if(dst.a >= .95f)
            break; 
     
        //advance the current position
        pos.xyz += Step;
     
        //break if the position is greater than <1, 1, 1>
        if(pos.x > 1.0f || pos.y > 1.0f || pos.z > 1.0f)
            break;
    }
 
    return dst;
}

POut PShader(VOut input)
{
	POut output;

	// Depth
	output.Depth = float4(0, 0, 0, 1.0f);

	// Normals
	output.Normals = float4(normalize(input.normal), 1);
	output.Position = float4(0, 0, 0, 1);
	output.Lighting = float4(1, 1, 1, 1);

	**CE_RESERVED_SHADER[PIXEL]**

	output.Diffuse = GetVRaycast(input);

	return output;
}

PS. Don't mind the weird things like **CE...

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Migi0027    4628

I usually don't work with for loops in shaders, but this one requires so.

 

But when I don't use a constant in the loop max, then the compilation takes hell of a while, hasn't compiled yet, so I stopped the program.

So changing to this:

for(int i = 0; i < Iterations; i++)

Why is that so?

 

EDIT: Well the compiler is trying to unroll an infinite loop, so it fails...

-MIGI0027

Edited by Migi0027

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Migi0027    4628

Nah stuff is still wrong, the reason for the foot to look better is because I cheated a bit:

for(int i = 0; i < Iterations; i++)
    {
        pos.w = 0;
        value = t_VolData.SampleLevel(ss, pos/4.1f, 1).r; // See that /4.1f, that the naughty stuff

It is supposed to look like this:

 

foot_thumb%5B11%5D.png?imgmax=800

 

 

Any help on this while I battle on?

-MIGI0027

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Styves    1792

A few things:

 

  • What format is your back/front textures? If it's 8bit you should scale to 0-1 range for output (if you're using HDR values then you should be fine).
  • Your position should be in texture space. That is, bias and scale it from [-1, 1] to [0, 1] (pos * 0.5 + 0.5) when you read your texture.

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      float3 randVec = _noise * 2.0f - 1.0f; // noise: vec: {[0;1], [0;1], 0} float3 tangent = normalize(randVec - normalVS * dot(randVec, normalVS)); float3 bitangent = cross(tangent, normalVS); float3x3 TBN = float3x3(tangent, bitangent, normalVS); float occlusion = 0.0; for (int i = 0; i < kernelSize; ++i) { float3 samplePos = samples[i].xyz; // samples: {[-1;1], [-1;1], [0;1]} samplePos = mul(samplePos, TBN); samplePos = positionVS.xyz + samplePos * ssaoRadius; float4 offset = float4(samplePos, 1.0f); offset = mul(offset, projectionMatrix); offset.xy /= offset.w; offset.y = -offset.y; offset.xy = offset.xy * 0.5f + 0.5f; float sampleDepth = tex_4.Sample(textureSampler, offset.xy).a; sampleDepth = vsPosFromDepth(sampleDepth, offset.xy).z; const float threshold = 0.025f; float rangeCheck = abs(positionVS.z - sampleDepth) < ssaoRadius ? 1.0 : 0.0; occlusion += (sampleDepth <= samplePos.z + threshold ? 1.0 : 0.0) * rangeCheck; } occlusion = saturate(1 - (occlusion / kernelSize)); And current result: http://imgur.com/UX2X1fc
      I will really appreciate for any advice!
    • By isu diss
       I'm trying to code Rayleigh part of Nishita's model (Display Method of the Sky Color Taking into Account Multiple Scattering). I get black screen no colors. Can anyone find the issue for me?
       
      #define InnerRadius 6320000 #define OutterRadius 6420000 #define PI 3.141592653 #define Isteps 20 #define Ksteps 10 static float3 RayleighCoeffs = float3(6.55e-6, 1.73e-5, 2.30e-5); RWTexture2D<float4> SkyColors : register (u0); cbuffer CSCONSTANTBUF : register( b0 ) { float fHeight; float3 vSunDir; } float Density(float Height) { return exp(-Height/8340); } float RaySphereIntersection(float3 RayOrigin, float3 RayDirection, float3 SphereOrigin, float Radius) { float t1, t0; float3 L = SphereOrigin - RayOrigin; float tCA = dot(L, RayDirection); if (tCA < 0) return -1; float lenL = length(L); float D2 = (lenL*lenL) - (tCA*tCA); float Radius2 = (Radius*Radius); if (D2<=Radius2) { float tHC = sqrt(Radius2 - D2); t0 = tCA-tHC; t1 = tCA+tHC; } else return -1; return t1; } float RayleighPhaseFunction(float cosTheta) { return ((3/(16*PI))*(1+cosTheta*cosTheta)); } float OpticalDepth(float3 StartPosition, float3 EndPosition) { float3 Direction = normalize(EndPosition - StartPosition); float RayLength = RaySphereIntersection(StartPosition, Direction, float3(0, 0, 0), OutterRadius); float SampleLength = RayLength / Isteps; float3 tmpPos = StartPosition + 0.5 * SampleLength * Direction; float tmp; for (int i=0; i<Isteps; i++) { tmp += Density(length(tmpPos)-InnerRadius); tmpPos += SampleLength * Direction; } return tmp*SampleLength; } static float fExposure = -2; float3 HDR( float3 LDR) { return 1.0f - exp( fExposure * LDR ); } [numthreads(32, 32, 1)] //disptach 8, 8, 1 it's 256 by 256 image void ComputeSky(uint3 DTID : SV_DispatchThreadID) { float X = ((2 * DTID.x) / 255) - 1; float Y = 1 - ((2 * DTID.y) / 255); float r = sqrt(((X*X)+(Y*Y))); float Theta = r * (PI); float Phi = atan2(Y, X); static float3 Eye = float3(0, 10, 0); float ViewOD = 0, SunOD = 0, tmpDensity = 0; float3 Attenuation = 0, tmp = 0, Irgb = 0; //if (r<=1) { float3 ViewDir = normalize(float3(sin(Theta)*cos(Phi), cos(Theta),sin(Theta)*sin(Phi) )); float ViewRayLength = RaySphereIntersection(Eye, ViewDir, float3(0, 0, 0), OutterRadius); float SampleLength = ViewRayLength / Ksteps; //vSunDir = normalize(vSunDir); float cosTheta = dot(normalize(vSunDir), ViewDir); float3 tmpPos = Eye + 0.5 * SampleLength * ViewDir; for(int k=0; k<Ksteps; k++) { float SunRayLength = RaySphereIntersection(tmpPos, vSunDir, float3(0, 0, 0), OutterRadius); float3 TopAtmosphere = tmpPos + SunRayLength*vSunDir; ViewOD = OpticalDepth(Eye, tmpPos); SunOD = OpticalDepth(tmpPos, TopAtmosphere); tmpDensity = Density(length(tmpPos)-InnerRadius); Attenuation = exp(-RayleighCoeffs*(ViewOD+SunOD)); tmp += tmpDensity*Attenuation; tmpPos += SampleLength * ViewDir; } Irgb = RayleighCoeffs*RayleighPhaseFunction(cosTheta)*tmp*SampleLength; SkyColors[DTID.xy] = float4(Irgb, 1); } }  
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