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Linear depth buffer for rendering shadows

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I have created a depth buffer with a shader resource view to use for only depth based shadows.
I render the world using only depth as it is seen from each shadowcasting light source.
The problem is that the depth buffer seems to be non linear by default.

Can I make the buffer linear without compability problems?

It there a fast function that can convert it to the real depth in HLSL?

Initialization of the depth buffer:
[code]
// Depth buffer
D3D11_TEXTURE2D_DESC DepthTextureDescription = {
NewWidth,//UINT Width;
NewHeight,//UINT Height;
1,//UINT MipLevels;
1,//UINT ArraySize;
DXGI_FORMAT_R32_TYPELESS,//DXGI_FORMAT Format;
1, 0,//DXGI_SAMPLE_DESC SampleDesc;
D3D11_USAGE_DEFAULT,//D3D11_USAGE Usage;
D3D11_BIND_DEPTH_STENCIL | D3D11_BIND_SHADER_RESOURCE,//UINT BindFlags;
0,//UINT CPUAccessFlags;
0//UINT MiscFlags;
};

// Depth buffer
if (m_pd3dDevice->CreateTexture2D( &DepthTextureDescription, NULL, &Surface->DepthBuffer ) != S_OK) {
::MessageBoxW(NULL,L"Could not create the depth atlas.",L"Internal error!",NULL);
}

// Depth I/O
D3D11_DEPTH_STENCIL_VIEW_DESC DepthIODescription = {
DXGI_FORMAT_D32_FLOAT,
D3D11_DSV_DIMENSION_TEXTURE2D,
0
};
if (m_pd3dDevice->CreateDepthStencilView( Surface->DepthBuffer, &DepthIODescription, &Surface->DepthInputAndOutput ) != S_OK) {
::MessageBoxW(NULL,L"Could not create depth stencil view for the depth atlas.",L"Internal error!",NULL);
}

// Depth output
D3D11_SHADER_RESOURCE_VIEW_DESC TextureOutputDescription = {
DXGI_FORMAT_R32_FLOAT,
D3D11_SRV_DIMENSION_TEXTURE2D,
0,
0
};
TextureOutputDescription.Texture2D.MipLevels = 1;
if (m_pd3dDevice->CreateShaderResourceView( Surface->DepthBuffer, &TextureOutputDescription, &Surface->DepthOutput ) != S_OK) {
::MessageBoxW(NULL,L"Could not create shader resource view for the depth atlas.",L"Internal error!",NULL);
}
[/code]

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If you want to store linear depth you have to create a render target and write linear depth to it using a shader.
Or at least, I never saw a way to do it with DepthStencilViews

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[quote name='TiagoCosta' timestamp='1309122334' post='4827996']If you want to store linear depth you have to create a render target and write linear depth to it using a shader.<br />Or at least, I never saw a way to do it with DepthStencilViews[/quote]

I have seen shadows being done with only a depth buffer in the DirectX SDK but I can't figure out how it works.

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[quote name='Dawoodoz' timestamp='1309122871' post='4828001']
[quote name='TiagoCosta' timestamp='1309122334' post='4827996']If you want to store linear depth you have to create a render target and write linear depth to it using a shader.<br />Or at least, I never saw a way to do it with DepthStencilViews[/quote]

I have seen shadows being done with only a depth buffer in the DirectX SDK but I can't figure out how it works.
[/quote]

Well, in my "engine" I render shadows with non-linear depth...

Why cant you use non-linear depth?
[url="http://wiki.gamedev.net/index.php/D3DBook:Shadows"][url="http://wiki.gamedev.net/index.php/D3DBook:Shadow_Maps"]
Check this link for some info on Shadow mapping[/url][/url]

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Check here for HLSL code to write linear depth: http://www.mvps.org/directx/articles/linear_z/linearz.htm

Note however that depth buffer precision is going to fall off closer to the near plane, which may give highy undesirable results.

Most shadow mapping samples you'll see will use the depth buffer, but there's no golden rule saying that you [i]have[/i] to, and you can in fact write regular non-linear depth (which could also double-up as a Z-prepass) to your depth buffer but write out the shadow info to a different render target.

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[quote name='TiagoCosta' timestamp='1309124355' post='4828007']
Why cant you use non-linear depth?
[/quote]

I don't know what non linear scale that is used by default nor how I can convert to and from it.
I must compare this unknown scale with a depth value from a linear matrix multiplication.

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[quote name='Dawoodoz' timestamp='1309125412' post='4828014']
I must compare this unknown scale with a depth value from a linear matrix multiplication.
[/quote]

No you don't.

You create the shadow map depth buffer using the object world matrix and the light view projection matrix right?

So, the values that you want to compare are the value stored in the depth buffer and a new non-linear depth calculated using the object matrix and the light view projection matrix...:cool:

EDIT: Dont forget that you have to divide the object xyz by the w to complete the projection before comparing!!!!

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[quote name='MJP' timestamp='1309134432' post='4828044']
[code]
// DepthBuffer is your depth-stencil buffer, Projection is your float4x4 projection matrix
float zw = DepthBuffer.Load(pixelCoord);
float linearZ = Projection._43 / (zw - Projection._33);
[/code]
[/quote]

The shadows are now working using that method. :)

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