//-------------------------------------------------------------------------------------
bool _IsAlphaAllOpaqueBC( _In_ const Image& cImage )
{
if ( !cImage.pixels )
return false;
// Image must be a multiple of 4 (degenerate cases of 1x1, 1x2, 2x1, and 2x2 are allowed)
size_t width = cImage.width;
if ( (width % 4) != 0 )
{
if ( width != 1 && width != 2 )
return false;
}
size_t height = cImage.height;
if ( (height % 4) != 0 )
{
if ( height != 1 && height != 2 )
return false;
}
// Promote "typeless" BC formats
DXGI_FORMAT cformat;
switch( cImage.format )
{
case DXGI_FORMAT_BC1_TYPELESS: cformat = DXGI_FORMAT_BC1_UNORM; break;
case DXGI_FORMAT_BC2_TYPELESS: cformat = DXGI_FORMAT_BC2_UNORM; break;
case DXGI_FORMAT_BC3_TYPELESS: cformat = DXGI_FORMAT_BC3_UNORM; break;
case DXGI_FORMAT_BC7_TYPELESS: cformat = DXGI_FORMAT_BC7_UNORM; break;
default: cformat = cImage.format; break;
}
// Determine BC format decoder
BC_DECODE pfDecode;
size_t sbpp;
switch(cformat)
{
case DXGI_FORMAT_BC1_UNORM:
case DXGI_FORMAT_BC1_UNORM_SRGB: pfDecode = D3DXDecodeBC1; sbpp = 8; break;
case DXGI_FORMAT_BC2_UNORM:
case DXGI_FORMAT_BC2_UNORM_SRGB: pfDecode = D3DXDecodeBC2; sbpp = 16; break;
case DXGI_FORMAT_BC3_UNORM:
case DXGI_FORMAT_BC3_UNORM_SRGB: pfDecode = D3DXDecodeBC3; sbpp = 16; break;
case DXGI_FORMAT_BC7_UNORM:
case DXGI_FORMAT_BC7_UNORM_SRGB: pfDecode = D3DXDecodeBC7; sbpp = 16; break;
default:
// BC4, BC5, and BC6 don't have alpha channels
return false;
}
// Scan blocks for non-opaque alpha
static const XMVECTORF32 threshold = { 0.99f, 0.99f, 0.99f, 0.99f };
XMVECTOR temp[16];
const uint8_t *pPixels = cImage.pixels;
for( size_t h=0; h < cImage.height; h += 4 )
{
const uint8_t *ptr = pPixels;
for( size_t count = 0; count < cImage.rowPitch; count += sbpp )
{
pfDecode( temp, ptr );
for( size_t j = 0; j < 16; ++j )
{
XMVECTOR alpha = XMVectorSplatW( temp[j] );
if ( XMVector4Less( alpha, threshold ) )
return false;
}
ptr += sbpp;
}
pPixels += cImage.rowPitch;
}
return true;
}
//-------------------------------------------------------------------------------------
bool _IsAlphaAllOpaqueBC( _In_ const Image& cImage )
{
if ( !cImage.pixels )
return false;
// Promote "typeless" BC formats
DXGI_FORMAT cformat;
switch( cImage.format )
{
case DXGI_FORMAT_BC1_TYPELESS: cformat = DXGI_FORMAT_BC1_UNORM; break;
case DXGI_FORMAT_BC2_TYPELESS: cformat = DXGI_FORMAT_BC2_UNORM; break;
case DXGI_FORMAT_BC3_TYPELESS: cformat = DXGI_FORMAT_BC3_UNORM; break;
case DXGI_FORMAT_BC7_TYPELESS: cformat = DXGI_FORMAT_BC7_UNORM; break;
default: cformat = cImage.format; break;
}
// Determine BC format decoder
BC_DECODE pfDecode;
size_t sbpp;
switch(cformat)
{
case DXGI_FORMAT_BC1_UNORM:
case DXGI_FORMAT_BC1_UNORM_SRGB: pfDecode = D3DXDecodeBC1; sbpp = 8; break;
case DXGI_FORMAT_BC2_UNORM:
case DXGI_FORMAT_BC2_UNORM_SRGB: pfDecode = D3DXDecodeBC2; sbpp = 16; break;
case DXGI_FORMAT_BC3_UNORM:
case DXGI_FORMAT_BC3_UNORM_SRGB: pfDecode = D3DXDecodeBC3; sbpp = 16; break;
case DXGI_FORMAT_BC7_UNORM:
case DXGI_FORMAT_BC7_UNORM_SRGB: pfDecode = D3DXDecodeBC7; sbpp = 16; break;
default:
// BC4, BC5, and BC6 don't have alpha channels
return false;
}
// Scan blocks for non-opaque alpha
static const XMVECTORF32 threshold = { 0.99f, 0.99f, 0.99f, 0.99f };
XMVECTOR temp[16];
const uint8_t *pPixels = cImage.pixels;
for( size_t h = 0; h < cImage.height; h += 4 )
{
const uint8_t *ptr = pPixels;
size_t ph = std::min<size_t>( 4, cImage.height - h );
size_t w = 0;
for( size_t count = 0; count < cImage.rowPitch; count += sbpp, w += 4 )
{
pfDecode( temp, ptr );
size_t pw = std::min<size_t>( 4, cImage.width - w );
assert( pw > 0 && ph > 0 );
if ( pw == 4 && ph == 4 )
{
// Full blocks
for( size_t j = 0; j < 16; ++j )
{
XMVECTOR alpha = XMVectorSplatW( temp[j] );
if ( XMVector4Less( alpha, threshold ) )
return false;
}
}
else
{
// Handle partial blocks
for( size_t y = 0; y < ph; ++y )
{
for( size_t x = 0; x < pw; ++x )
{
XMVECTOR alpha = XMVectorSplatW( temp[ y * 4 + x ] );
if ( XMVector4Less( alpha, threshold ) )
return false;
}
}
}
ptr += sbpp;
}
pPixels += cImage.rowPitch;
}
return true;
}
