axmol/cocos2dx/platform/third_party/common/s3tc/s3tc.cpp

/****************************************************************************
 Copyright (c) 2010 cocos2d-x.org
 
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#include "s3tc.h"

void s3tc_decode_block(uint8_t **block_data,
                       uint32_t *decode_block_data,
                       unsigned int stride,
                       bool oneBitAlphaFlag,
                       uint64_t alpha,
                       S3TCDecodeFlag decodeFlag)
{
    unsigned int colorValue0 = 0 , colorValue1 = 0, initAlpha = (!oneBitAlphaFlag * 255u) << 24;
    unsigned int rb0 = 0, rb1 = 0, rb2 = 0, rb3 = 0, g0 = 0, g1 = 0, g2 = 0, g3 = 0;
    
    uint32_t colors[4], pixelsIndex = 0;
    
    /* load the two color values*/
    memcpy((void *)&colorValue0, *block_data, 2);
    (*block_data) += 2;
    
    memcpy((void *)&colorValue1, *block_data, 2);
    (*block_data) += 2;
    
    /* the channel is r5g6b5 , 16 bits */
    rb0  = (colorValue0<<19 | colorValue0>>8) & 0xf800f8;
    rb1  = (colorValue1<<19 | colorValue1>>8) & 0xf800f8;
    g0   =         (colorValue0 <<5) & 0x00fc00;
    g1   =         (colorValue1 <<5) & 0x00fc00;
    g0  +=         (g0 >>6) & 0x000300;
    g1  +=         (g1 >>6) & 0x000300;
    
    colors[0] = rb0 + g0 + initAlpha;
    colors[1] = rb1 + g1 + initAlpha;
    
    /* interpolate the other two color values */
    if (colorValue0 > colorValue1 || oneBitAlphaFlag)
    {
        rb2 = (((2*rb0+rb1) * 21) >> 6) & 0xff00ff;
        rb3 = (((2*rb1+rb0) * 21) >> 6) & 0xff00ff;
        g2  = (((2*g0 +g1 ) * 21) >> 6) & 0x00ff00;
        g3  = (((2*g1 +g0 ) * 21) >> 6) & 0x00ff00;
        colors[3] = rb3 + g3 + initAlpha;
    }
    else
    {
        rb2 = ((rb0+rb1) >> 1) & 0xff00ff;
        g2  = ((g0 +g1 ) >> 1) & 0x00ff00;
        colors[3] = 0;
    }
    colors[2] = rb2 + g2 + initAlpha;
    
    /*read the pixelsIndex , 2bits per pixel, 4 bytes */
    memcpy((void*)&pixelsIndex, *block_data, 4);
    (*block_data) += 4;
    
    if( S3TCDecodeFlag::dxt5 == decodeFlag)
    {
        //dxt5 use interpolate alpha
        // 8-Alpha block: derive the other six alphas.
        // Bit code 000 = alpha0, 001 = alpha1, other are interpolated.
        
        unsigned int alphaArray[8];
        
        alphaArray[0] = (alpha )& 0xff ;
        alphaArray[1] = (alpha >> 8)& 0xff ;
        
        if(alphaArray[0] >= alphaArray[1])
        {
            alphaArray[2] = (alphaArray[0]*6 + alphaArray[1]*1)/7;
            alphaArray[3] = (alphaArray[0]*5 + alphaArray[1]*2)/7;
            alphaArray[4] = (alphaArray[0]*4 + alphaArray[1]*3)/7;
            alphaArray[5] = (alphaArray[0]*3 + alphaArray[1]*4)/7;
            alphaArray[6] = (alphaArray[0]*2 + alphaArray[1]*5)/7;
            alphaArray[7] = (alphaArray[0]*1 + alphaArray[1]*6)/7;
        }
        else if(alphaArray[0] < alphaArray[1])
        {
            alphaArray[2] = (alphaArray[0]*4 + alphaArray[1]*1)/5;
            alphaArray[3] = (alphaArray[0]*3 + alphaArray[1]*2)/5;
            alphaArray[4] = (alphaArray[0]*2 + alphaArray[1]*3)/5;
            alphaArray[5] = (alphaArray[0]*1 + alphaArray[1]*4)/5;
            alphaArray[6] = 0;
            alphaArray[7] = 255;
        }
        
        // read the flowing 48bit indices (16*3)
        alpha >>= 16;
        
        for (int y=0; y<4; y++)
        {
            for (int x=0; x<4; x++)
            {
                decode_block_data[x] = (alphaArray[alpha & 5] <<24) + colors[pixelsIndex & 3];
                pixelsIndex >>= 2;
                alpha >>= 3;
            }
            decode_block_data += stride;
        }
    } //if (dxt5 == comFlag)
    else
    { //dxt1 dxt3 use explicit alpha
        for (int y=0; y<4; y++)
        {
            for (int x=0; x<4; x++)
            {
                initAlpha   = (alpha & 0x0f) << 28;
                initAlpha   += initAlpha >> 4;
                decode_block_data[x] = initAlpha + colors[pixelsIndex& 3];
                pixelsIndex >>= 2;
                alpha       >>= 4;
            }
            decode_block_data += stride;
        }
    }
}

void s3tc_decode(uint8_t *encode_data,             //in_data
                 uint8_t *decode_data,             //out_data
                 const unsigned int pixelsWidth,
                 const unsigned int pixelsHeight,
                 S3TCDecodeFlag decodeFlag)
{
    uint32_t *decode_block_data = (uint32_t *)decode_data;
    for( int block_y =0 ; block_y < pixelsHeight/4; block_y++,decode_block_data += 3*pixelsWidth)   //stride = 3*width
    {
        for( int block_x =0 ; block_x < pixelsWidth/4; block_x++,decode_block_data += 4)            //skip 4 pixels
        {
            uint64_t blockAlpha = 0;
            
            switch (decodeFlag) {
                case S3TCDecodeFlag::dxt1:
                {
                    s3tc_decode_block(&encode_data, decode_block_data, pixelsWidth, 0, 0LL, S3TCDecodeFlag::dxt1);
                }
                    break;
                case S3TCDecodeFlag::dxt3:
                {
                    memcpy((void *)&blockAlpha, encode_data, 8);
                    encode_data +=8;
                    s3tc_decode_block(&encode_data, decode_block_data, pixelsWidth, 1, blockAlpha,S3TCDecodeFlag::dxt3);
                }
                    break;
                case S3TCDecodeFlag::dxt5:
                {
                    memcpy((void *)&blockAlpha, encode_data , 8);
                    encode_data += 8;
                    s3tc_decode_block(&encode_data, decode_block_data, pixelsWidth, 1, blockAlpha, S3TCDecodeFlag::dxt5);
                }
                    break;
                default:
                    break;
            }//switch
        }//for block_x
    }//for block_y
}