MipMapCount == 0 ? #43

Activity

1. mikeeheler commented on Dec 20, 2016

   

   Mike Eheler (mikeeheler)

   on Dec 20, 2016

   Author

   More actions

   Adding to this I have also noticed the DDS_HEADER.dwCaps DDSCAPS_MIPMAP flag. DirectXTexDDS.cpp sets this flag if dwMipMapCount is > 1, a truly mipmapped texture, while it basically always sets DDS_HEADER_FLAGS_MIPMAP and sets DDS_HEADER.dwMipMapCount to 1 or more.
2. Chuck Walbourn (walbourn)

   added

   question

   on Dec 21, 2016
3. walbourn commented on Dec 21, 2016

   

   Chuck Walbourn (walbourn)

   on Dec 21, 2016

   Last edited by walbourn

   Collaborator

   More actions

   The DDS file format is not particularly well specified. I have made sure the basics are on MSDN, but it's largely a matter of trying to match "What does the legacy D3DX9, D3DX10, and/or D3DX11 library do?". In some places where the original behavior was a little lose, I tried to be a bit more consistent with DirectXTex.

   In the original D3DX9 code it writes DDS headers as follows:

   DDS_HEADER Header;
   memset(&Header, 0x00, sizeof(DDS_HEADER));
   
   Header.dwSize   = sizeof(DDS_HEADER);
   Header.dwFlags  = DDS_DDSD_HEIGHT | DDS_DDSD_WIDTH | DDS_DDSD_PIXELFORMAT | DDS_DDSD_CAPS;
   Header.dwHeight = (DWORD) m_uHeight;
   Header.dwWidth  = (DWORD) m_uWidth;
   Header.ddpf     = pFormatDDPF->ddpf;
   Header.dwCaps   = DDS_CAPS_TEXTURE;
   
   if(pFormatDDPF->ddpf.dwFlags & (DDS_DDPF_ALPHAPIXELS | DDS_DDPF_ALPHA))
       Header.dwCaps |= DDS_CAPS_ALPHA;
   
   if(pFormatDDPF->ddpf.dwFlags & (DDS_DDPF_PALETTEINDEXED8))
       Header.dwCaps |= DDS_CAPS_PALETTE;
   
   if(m_pMip)
   {
       Header.dwFlags |= DDS_DDSD_MIPMAPCOUNT;
       Header.dwMipMapCount = (DWORD) uMipLevels;
       Header.dwCaps |= DDS_CAPS_COMPLEX | DDS_CAPS_MIPMAP;
   }
   
   if(m_pFace)
   {
       Header.dwCaps |= DDS_CAPS_COMPLEX;
       Header.dwCaps2 |= DDS_CAPS2_CUBEMAP | DDS_CAPS2_CUBEMAP_ALLFACES;
   }
   
   if(m_uDepth > 1)
   {
       Header.dwFlags |= DDS_DDSD_DEPTH;
       Header.dwDepth = (DWORD) m_uDepth;
       Header.dwCaps2 |= DDS_CAPS2_VOLUME;
   }
   

   When reading DDS files, D3DX9 does this with respect to the mipmaps (it reads dwMipMapCount whether or not the flags included DDS_DDSD_MIPMAPCOUNT, treating 0 as 1).

   // Grok levels
   UINT cMipLevels;
   cMipLevels = (UINT) pHeader->dwMipMapCount;
   
   if(0 == cMipLevels)
       cMipLevels = 1
   

   Therefore that's the behavior I implemented for DirectXTex.

   The writing code was rewritten for D3DX10 (and carried forward to D3DX11) to add the DX10 extension header but it does the same basic thing. Here's writing a DDS header (you'll note it doesn't bother setting DDS_DDSD_MIPMAPCOUNT at all).

   ZeroMemory(&fileHeader, sizeof(fileHeader));
   fileHeader.dwMagic = MAKEFOURCC('D', 'D', 'S', ' ');
   fileHeader.header.ddpf = pFormat->ddpf;
   fileHeader.header.dwCaps = DDS_CAPS_TEXTURE;
   if (m_cMipmaps > 1)
       fileHeader.header.dwCaps |= DDS_CAPS_MIPMAP;
   
   fileHeader.header.dwFlags |= DDS_DDSD_HEIGHT | DDS_DDSD_WIDTH;
   fileHeader.header.dwWidth = m_Width;
   fileHeader.header.dwHeight = m_Height;
   fileHeader.header.dwLinearSize = m_Stride;
   fileHeader.header.dwDepth = m_Depth;
   fileHeader.header.dwMipMapCount = m_cMipmaps;
   fileHeader.header.dwSize = sizeof(DDS_HEADER);
   
   switch(m_ResType)
   {
   case D3D10_RESOURCE_DIMENSION_TEXTURE3D:
       fileHeader.header.dwFlags |= DDS_DDSD_DEPTH;
       fileHeader.header.dwCaps |= DDS_CAPS_COMPLEX;
       fileHeader.header.dwCaps2 |= DDS_CAPS2_VOLUME;
       break;
   
   case D3D10_RESOURCE_DIMENSION_TEXTURE2D:
       if (m_bIsCubemap)
       {
           fileHeader.header.dwCaps |= DDS_CAPS_COMPLEX; 
           fileHeader.header.dwCaps2 |= DDS_CAPS2_CUBEMAP | DDS_CAPS2_CUBEMAP_ALLFACES;
       }
       break;
   
   case D3D10_RESOURCE_DIMENSION_TEXTURE1D:
       break;
   
   default:
       VNASSERT(0);
       break;
   }
   

   The D3DX10 and D3DX11 header parsing code is the same as it was in D3DX9 with respect to the mipmapcount.

   The DirectXTex texconv behavior is also based on the legacy DirectX SDK command-line tool of the same name, which is why it defaults to generating all mipmaps (i.e. -m 0) when writing out a DDS file.
4. Chuck Walbourn (walbourn)

   closed this as completedon Dec 21, 2016
5. mikeeheler commented on Dec 21, 2016

   

   Mike Eheler (mikeeheler)

   on Dec 21, 2016

   Author

   More actions

   Great! Thank you for the thorough response, Chuck. It's very appreciated.