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