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DX11 Locking lowest mip levels of a DXT texture

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Hi, I'm writing a cross platform engine (GL, GL ES, DX9, DX10, DX11), I've got a Texture class with a Lock and Unlock method, in directX, depending on the pool & usage some textures can be locked directly and some cannot and must use a temporary "staging" texture ( or surface for locking a single mip level ), this works perfectly, except with DX9...

In (more or less) pseudo code this look like this (Considering only the particular case of a DXT texture in D3DPOOL_DEFAULT which cannot be locked directly):

Texture::Lock( u32 _mipLevel )
u32 mipWidth, mipHeight;
GetMipMapDimensions( _mipLevel, mipWidth, mipHeight );

//DX9 complains about creating DXT textures less than 4x4 in size
mipWidth = Max( mipWidth, 4 );
mipHeight = Max( mipHeight, 4 );

pDevice->CreateTexture( mipWidth, mipHeight,
1,//mip maps
&m_pStagingTexture, NULL );

m_pStagingTexture->Lock( ... );

Texture::Unlock( u32 _mipLevel )
if( m_pStagingTexture )
m_pStagingTexture->UnlockRect( 0 );

IDirect3DSurface9* pStagingSurface;
IDirect3DSurface9* pDestSurface;

m_pStagingTexture->GetSurfaceLevel( 0, &pStagingSurface );

((IDirect3DTexture9*)m_pTex)->GetSurfaceLevel( _mipLevel, &pDestSurface );

//Here I also tried to call UpdateSurface with various parameters for pSourceRect and pDestinationPoint instead of NULL, with no success :(
pDevice->UpdateSurface( pStagingSurface, NULL, pDestSurface, NULL );

SAFE_RELEASE( m_pStagingTexture )



This works nicely for uncompressed formats, but this breaks when locking the lowest mip levels (1x1 and 2x2) because of the DXT 4x4 block size

if TRY_FORCING_MINIMUM_STAGING_TEX_SIZE is NOT defined I get "Direct3D9: (ERROR) :DXT Formats require width/height to be a multiple of 4. CreateTexture failed." while creating the staging texture

if TRY_FORCING_MINIMUM_STAGING_TEX_SIZE is defined I get "Direct3D9: (ERROR) :pRect doesn't fit inside the surface" while calling UpdateSurface

I think I could get away by creating a staging texture with the full mip chain instead of only the mip level I'm locking and then using UpdateTexture instead of UpdateSurface but this would be very sub-optimal as well as making my code kind-of ugly

Do you know a solution to this problem ? ( I could eventually use D3DPOOL_MANAGED textures and lock them directly, but I'd rather avoid that solution if possible )

Thanks in advance

Florent Tournade

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