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Generating mipmaps automatically

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#1 jajcek   Members   


Posted 30 December 2012 - 02:43 PM


I am completely new to the mipmapping technique. I have read some documents over the MSDN, but somehow I cannot connect all of the pieces together.

I'd like to have generated mipmaps for my terrain. I have a DDS texture which is loaded by using:

HRESULT CreateDDSTextureFromFile( _In_ ID3D11Device*, _In_z_ const wchar_t*,  _Out_opt_ ID3D11Resource**, _Out_opt_ ID3D11ShaderResourceView**, _In_ size_t maxsize = 0 )

from DirectXTK. So, by reading the document http://msdn.microsoft.com/en-us/library/windows/desktop/bb205131(v=vs.85).aspx I wrote such code:

_result = CreateDDSTextureFromFile( device, filename, &_texture, NULL );
_texture->GetType( &type );
if( type == D3D11_RESOURCE_DIMENSION_TEXTURE2D ) {    
    D3D11_TEXTURE2D_DESC desc;    
    ID3D11Texture2D *pTexture2D = (ID3D11Texture2D*)_texture;    
    pTexture2D->GetDesc( &desc );    
    srvDesc.Format = desc.Format;    
    srvDesc.ViewDimension = D3D11_SRV_DIMENSION_TEXTURE2D;    
    srvDesc.Texture2D.MipLevels = desc.MipLevels; // when I put here 0 I can't see my terrain    
    srvDesc.Texture2D.MostDetailedMip = desc.MipLevels - 1;    
    ID3D11ShaderResourceView *pSRView = NULL;    device->CreateShaderResourceView( _texture, &srvDesc, &m_texture );}

after that, in the place where I pass resources to shaders I put:

// ...

deviceContext->Unmap( m_lightBuffer, 0 );

// here is what I add, the "texture" is the "m_texture" from the code above
deviceContext->GenerateMips( texture ); 

deviceContext->PSSetConstantBuffers( 0, 1, &m_lightBuffer ); 
deviceContext->PSSetShaderResources(0, 1, &texture); 

// ...

but it doesn't work, when I put to MipLevels 0 as it was written in some document to generate mipmaps my terrain doesn't show up. When I leave it with desc.MipLevels there are no mipmaps. What step did I overlook?

Thank you.

#2 MJP   Moderators   


Posted 30 December 2012 - 08:37 PM

Okay you have a few problems here:


1. If you look at the source for the DDS texture loader, you'll see that it creates the texture with the number of mipmaps present in the DDS file. So if it has a full mip chain in the file the texture will have the full mip chain, however if there's only one mip level then your texture will only have 1 mip level. You can't alter the number of mip levels by creating a new shader resource view, the shader resource view can only view the mips that are available in the texture resource.

2. If you read the docs for GenerateMips it says that it can only be called with a texture that was created with D3D11_BIND_RENDER_TARGET and D3D11_RESOURCE_MISC_GENERATE_MIPS. The DDS texture loader does not do this, so it will fail. You should create your device with the D3D11_CREATE_DEVICE_DEBUG flag, which will cause D3D to output error messages when you do things like this.


3. 0 is not a valid parameter for the MipLevels member when creating a shader resource view for a Texture2D. Like I said before, an SRV cannot modify a texture: it just views some portion of a texture. By specifying 0, you're saying "I don't want to be able to view any mip levels of this texture" which obviously doesn't make sense, which is why it's not valid. You should create the device with DEBUG flag, and/or check the return value of CreateShaderResourceView so that you know when a call fails.

When you say "MipLevels 0 as it was written in some document to generate mipmaps", you're probably referring to the documentation for D3D11_TEXTURE2D_DESC which is a completely different structure passed to a different function. The DDS texture loader is what calls CreateTexture2D, so you'll either need to modify that code or create a new texture and copy the data for the first mip level to your new texture. If you do either of those, then you can create the texture with the full mipchain as well as the flags needed for GenerateMips to be called.

#3 jajcek   Members   


Posted 31 December 2012 - 02:57 AM

Thank you for your answer. I have finally solved it an I thought that it will be good to share this to others that are using DirectXTK.
The DirectXTK has another function:

HRESULT CreateDDSTextureFromFileEx( _In_ ID3D11Device* d3dDevice,
                                        _In_z_ const wchar_t* szFileName,
                                        _In_ size_t maxsize,
                                        _In_ D3D11_USAGE usage,
                                        _In_ unsigned int bindFlags,
                                        _In_ unsigned int cpuAccessFlags,
                                        _In_ unsigned int miscFlags,
                                        _In_ bool forceSRGB,
                                        _Out_opt_ ID3D11Resource** texture,
                                        _Out_opt_ ID3D11ShaderResourceView** textureView

to this function I can pass the required flags, as you said the D3D11_BIND_RENDER_TARGET and the D3D11_RESOURCE_MISC_GENERATE_MIPS.

I have created a DDS with custom mipmaps that differs a lot from the original picture, so I could clearly see that on a terrain. When I called GenerateMips the mipmaps from DDS has been hid by the generated ones (I think so :D), so it means that it finally works.

Edited by jajcek, 31 December 2012 - 03:00 AM.

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