349 lines
8 KiB
C++
349 lines
8 KiB
C++
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/* -----------------------------------------------------------------------------
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Copyright (c) 2006 Simon Brown si@sjbrown.co.uk
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Permission is hereby granted, free of charge, to any person obtaining
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a copy of this software and associated documentation files (the
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"Software"), to deal in the Software without restriction, including
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without limitation the rights to use, copy, modify, merge, publish,
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distribute, sublicense, and/or sell copies of the Software, and to
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permit persons to whom the Software is furnished to do so, subject to
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the following conditions:
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The above copyright notice and this permission notice shall be included
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in all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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-------------------------------------------------------------------------- */
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#include "alpha.h"
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#include <algorithm>
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namespace squish {
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static int FloatToInt( float a, int limit )
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{
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// use ANSI round-to-zero behaviour to get round-to-nearest
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int i = ( int )( a + 0.5f );
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// clamp to the limit
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if( i < 0 )
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i = 0;
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else if( i > limit )
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i = limit;
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// done
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return i;
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}
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void CompressAlphaDxt3( u8 const* rgba, int mask, void* block )
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{
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u8* bytes = reinterpret_cast< u8* >( block );
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// quantise and pack the alpha values pairwise
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for( int i = 0; i < 8; ++i )
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{
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// quantise down to 4 bits
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float alpha1 = ( float )rgba[8*i + 3] * ( 15.0f/255.0f );
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float alpha2 = ( float )rgba[8*i + 7] * ( 15.0f/255.0f );
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int quant1 = FloatToInt( alpha1, 15 );
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int quant2 = FloatToInt( alpha2, 15 );
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// set alpha to zero where masked
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int bit1 = 1 << ( 2*i );
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int bit2 = 1 << ( 2*i + 1 );
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if( ( mask & bit1 ) == 0 )
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quant1 = 0;
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if( ( mask & bit2 ) == 0 )
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quant2 = 0;
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// pack into the byte
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bytes[i] = ( u8 )( quant1 | ( quant2 << 4 ) );
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}
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}
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void DecompressAlphaDxt3( u8* rgba, void const* block )
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{
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u8 const* bytes = reinterpret_cast< u8 const* >( block );
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// unpack the alpha values pairwise
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for( int i = 0; i < 8; ++i )
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{
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// quantise down to 4 bits
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u8 quant = bytes[i];
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// unpack the values
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u8 lo = quant & 0x0f;
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u8 hi = quant & 0xf0;
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// convert back up to bytes
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rgba[8*i + 3] = lo | ( lo << 4 );
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rgba[8*i + 7] = hi | ( hi >> 4 );
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}
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}
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static void FixRange( int& min, int& max, int steps )
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{
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if( max - min < steps )
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max = std::min( min + steps, 255 );
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if( max - min < steps )
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min = std::max( 0, max - steps );
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}
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static int FitCodes( u8 const* rgba, int mask, u8 const* codes, u8* indices )
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{
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// fit each alpha value to the codebook
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int err = 0;
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for( int i = 0; i < 16; ++i )
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{
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// check this pixel is valid
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int bit = 1 << i;
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if( ( mask & bit ) == 0 )
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{
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// use the first code
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indices[i] = 0;
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continue;
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}
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// find the least error and corresponding index
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int value = rgba[4*i + 3];
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int least = 2147483647; //INT_MAX
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int index = 0;
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for( int j = 0; j < 8; ++j )
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{
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// get the squared error from this code
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int dist = ( int )value - ( int )codes[j];
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dist *= dist;
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// compare with the best so far
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if( dist < least )
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{
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least = dist;
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index = j;
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}
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}
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// save this index and accumulate the error
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indices[i] = ( u8 )index;
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err += least;
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}
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// return the total error
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return err;
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}
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static void WriteAlphaBlock( int alpha0, int alpha1, u8 const* indices, void* block )
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{
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u8* bytes = reinterpret_cast< u8* >( block );
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// write the first two bytes
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bytes[0] = ( u8 )alpha0;
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bytes[1] = ( u8 )alpha1;
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// pack the indices with 3 bits each
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u8* dest = bytes + 2;
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u8 const* src = indices;
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for( int i = 0; i < 2; ++i )
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{
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// pack 8 3-bit values
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int value = 0;
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for( int j = 0; j < 8; ++j )
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{
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int index = *src++;
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value |= ( index << 3*j );
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}
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// store in 3 bytes
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for( int j = 0; j < 3; ++j )
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{
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int byte = ( value >> 8*j ) & 0xff;
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*dest++ = ( u8 )byte;
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}
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}
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}
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static void WriteAlphaBlock5( int alpha0, int alpha1, u8 const* indices, void* block )
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{
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// check the relative values of the endpoints
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if( alpha0 > alpha1 )
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{
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// swap the indices
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u8 swapped[16];
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for( int i = 0; i < 16; ++i )
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{
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u8 index = indices[i];
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if( index == 0 )
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swapped[i] = 1;
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else if( index == 1 )
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swapped[i] = 0;
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else if( index <= 5 )
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swapped[i] = 7 - index;
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else
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swapped[i] = index;
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}
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// write the block
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WriteAlphaBlock( alpha1, alpha0, swapped, block );
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}
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else
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{
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// write the block
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WriteAlphaBlock( alpha0, alpha1, indices, block );
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}
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}
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static void WriteAlphaBlock7( int alpha0, int alpha1, u8 const* indices, void* block )
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{
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// check the relative values of the endpoints
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if( alpha0 < alpha1 )
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{
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// swap the indices
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u8 swapped[16];
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for( int i = 0; i < 16; ++i )
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{
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u8 index = indices[i];
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if( index == 0 )
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swapped[i] = 1;
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else if( index == 1 )
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swapped[i] = 0;
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else
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swapped[i] = 9 - index;
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}
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// write the block
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WriteAlphaBlock( alpha1, alpha0, swapped, block );
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}
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else
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{
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// write the block
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WriteAlphaBlock( alpha0, alpha1, indices, block );
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}
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}
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void CompressAlphaDxt5( u8 const* rgba, int mask, void* block )
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{
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// get the range for 5-alpha and 7-alpha interpolation
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int min5 = 255;
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int max5 = 0;
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int min7 = 255;
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int max7 = 0;
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for( int i = 0; i < 16; ++i )
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{
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// check this pixel is valid
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int bit = 1 << i;
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if( ( mask & bit ) == 0 )
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continue;
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// incorporate into the min/max
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int value = rgba[4*i + 3];
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if( value < min7 )
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min7 = value;
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if( value > max7 )
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max7 = value;
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if( value != 0 && value < min5 )
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min5 = value;
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if( value != 255 && value > max5 )
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max5 = value;
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}
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// handle the case that no valid range was found
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if( min5 > max5 )
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min5 = max5;
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if( min7 > max7 )
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min7 = max7;
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// fix the range to be the minimum in each case
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FixRange( min5, max5, 5 );
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FixRange( min7, max7, 7 );
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// set up the 5-alpha code book
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u8 codes5[8];
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codes5[0] = ( u8 )min5;
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codes5[1] = ( u8 )max5;
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for( int i = 1; i < 5; ++i )
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codes5[1 + i] = ( u8 )( ( ( 5 - i )*min5 + i*max5 )/5 );
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codes5[6] = 0;
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codes5[7] = 255;
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// set up the 7-alpha code book
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u8 codes7[8];
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codes7[0] = ( u8 )min7;
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codes7[1] = ( u8 )max7;
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for( int i = 1; i < 7; ++i )
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codes7[1 + i] = ( u8 )( ( ( 7 - i )*min7 + i*max7 )/7 );
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// fit the data to both code books
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u8 indices5[16];
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u8 indices7[16];
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int err5 = FitCodes( rgba, mask, codes5, indices5 );
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int err7 = FitCodes( rgba, mask, codes7, indices7 );
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// save the block with least error
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if( err5 <= err7 )
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WriteAlphaBlock5( min5, max5, indices5, block );
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else
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WriteAlphaBlock7( min7, max7, indices7, block );
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}
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void DecompressAlphaDxt5( u8* rgba, void const* block )
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{
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// get the two alpha values
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u8 const* bytes = reinterpret_cast< u8 const* >( block );
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int alpha0 = bytes[0];
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int alpha1 = bytes[1];
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// compare the values to build the codebook
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u8 codes[8];
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codes[0] = ( u8 )alpha0;
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codes[1] = ( u8 )alpha1;
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if( alpha0 <= alpha1 )
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{
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// use 5-alpha codebook
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for( int i = 1; i < 5; ++i )
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codes[1 + i] = ( u8 )( ( ( 5 - i )*alpha0 + i*alpha1 )/5 );
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codes[6] = 0;
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codes[7] = 255;
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}
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else
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{
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// use 7-alpha codebook
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for( int i = 1; i < 7; ++i )
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codes[1 + i] = ( u8 )( ( ( 7 - i )*alpha0 + i*alpha1 )/7 );
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}
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// decode the indices
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u8 indices[16];
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u8 const* src = bytes + 2;
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u8* dest = indices;
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for( int i = 0; i < 2; ++i )
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{
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// grab 3 bytes
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int value = 0;
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for( int j = 0; j < 3; ++j )
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{
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int byte = *src++;
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value |= ( byte << 8*j );
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}
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// unpack 8 3-bit values from it
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for( int j = 0; j < 8; ++j )
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{
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int index = ( value >> 3*j ) & 0x7;
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*dest++ = ( u8 )index;
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}
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}
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// write out the indexed codebook values
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for( int i = 0; i < 16; ++i )
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rgba[4*i + 3] = codes[indices[i]];
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}
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} // namespace squish
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