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Migi0027

DX11
DX11 - Volume Rendering - Article Misunderstanding

23 posts in this topic

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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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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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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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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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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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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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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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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I see that the repeating pattern dissapears when scaling the vertices (3rd party program), to 1/4th of the original size. But then the resolution is terrible.

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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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