File: colourblock.cpp

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/* -----------------------------------------------------------------------------

    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 "colourblock.h"

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;
}

static int FloatTo565( Vec3::Arg colour )
{
    // get the components in the correct range
    int r = FloatToInt( 31.0f*colour.X(), 31 );
    int g = FloatToInt( 63.0f*colour.Y(), 63 );
    int b = FloatToInt( 31.0f*colour.Z(), 31 );

    // pack into a single value
    return ( r << 11 ) | ( g << 5 ) | b;
}

static void WriteColourBlock( int a, int b, u8* indices, void* block )
{
    // get the block as bytes
    u8* bytes = ( u8* )block;

    // write the endpoints
    bytes[0] = ( u8 )( a & 0xff );
    bytes[1] = ( u8 )( a >> 8 );
    bytes[2] = ( u8 )( b & 0xff );
    bytes[3] = ( u8 )( b >> 8 );

    // write the indices
    for( int i = 0; i < 4; ++i )
    {
        u8 const* ind = indices + 4*i;
        bytes[4 + i] = ind[0] | ( ind[1] << 2 ) | ( ind[2] << 4 ) | ( ind[3] << 6 );
    }
}

void WriteColourBlock3( Vec3::Arg start, Vec3::Arg end, u8 const* indices, void* block )
{
    // get the packed values
    int a = FloatTo565( start );
    int b = FloatTo565( end );

    // remap the indices
    u8 remapped[16];
    if( a <= b )
    {
        // use the indices directly
        for( int i = 0; i < 16; ++i )
            remapped[i] = indices[i];
    }
    else
    {
        // swap a and b
        std::swap( a, b );
        for( int i = 0; i < 16; ++i )
        {
            if( indices[i] == 0 )
                remapped[i] = 1;
            else if( indices[i] == 1 )
                remapped[i] = 0;
            else
                remapped[i] = indices[i];
        }
    }

    // write the block
    WriteColourBlock( a, b, remapped, block );
}

void WriteColourBlock4( Vec3::Arg start, Vec3::Arg end, u8 const* indices, void* block )
{
    // get the packed values
    int a = FloatTo565( start );
    int b = FloatTo565( end );

    // remap the indices
    u8 remapped[16];
    if( a < b )
    {
        // swap a and b
        std::swap( a, b );
        for( int i = 0; i < 16; ++i )
            remapped[i] = ( indices[i] ^ 0x1 ) & 0x3;
    }
    else if( a == b )
    {
        // use index 0
        for( int i = 0; i < 16; ++i )
            remapped[i] = 0;
    }
    else
    {
        // use the indices directly
        for( int i = 0; i < 16; ++i )
            remapped[i] = indices[i];
    }

    // write the block
    WriteColourBlock( a, b, remapped, block );
}

static int Unpack565( u8 const* packed, u8* colour )
{
    // build the packed value
    int value = ( int )packed[0] | ( ( int )packed[1] << 8 );

    // get the components in the stored range
    u8 red = ( u8 )( ( value >> 11 ) & 0x1f );
    u8 green = ( u8 )( ( value >> 5 ) & 0x3f );
    u8 blue = ( u8 )( value & 0x1f );

    // scale up to 8 bits
    colour[0] = ( red << 3 ) | ( red >> 2 );
    colour[1] = ( green << 2 ) | ( green >> 4 );
    colour[2] = ( blue << 3 ) | ( blue >> 2 );
    colour[3] = 255;

    // return the value
    return value;
}

void DecompressColour( u8* rgba, void const* block, bool isDxt1 )
{
    // get the block bytes
    u8 const* bytes = reinterpret_cast< u8 const* >( block );

    // unpack the endpoints
    u8 codes[16];
    int a = Unpack565( bytes, codes );
    int b = Unpack565( bytes + 2, codes + 4 );

    // generate the midpoints
    for( int i = 0; i < 3; ++i )
    {
        int c = codes[i];
        int d = codes[4 + i];

        if( isDxt1 && a <= b )
        {
            codes[8 + i] = ( u8 )( ( c + d )/2 );
            codes[12 + i] = 0;
        }
        else
        {
            codes[8 + i] = ( u8 )( ( 2*c + d )/3 );
            codes[12 + i] = ( u8 )( ( c + 2*d )/3 );
        }
    }

    // fill in alpha for the intermediate values
    codes[8 + 3] = 255;
    codes[12 + 3] = ( isDxt1 && a <= b ) ? 0 : 255;

    // unpack the indices
    u8 indices[16];
    for( int i = 0; i < 4; ++i )
    {
        u8* ind = indices + 4*i;
        u8 packed = bytes[4 + i];

        ind[0] = packed & 0x3;
        ind[1] = ( packed >> 2 ) & 0x3;
        ind[2] = ( packed >> 4 ) & 0x3;
        ind[3] = ( packed >> 6 ) & 0x3;
    }

    // store out the colours
    for( int i = 0; i < 16; ++i )
    {
        u8 offset = 4*indices[i];
        for( int j = 0; j < 4; ++j )
            rgba[4*i + j] = codes[offset + j];
    }
}

} // namespace squish