// from kis_image.cc

void KisImage::convertTileToPixmap(KisLayer *lay, int tileNo, QPixmap *pix)
{
    /* Copy the composite image into a QImage so it can be 
    converted to a QPixmap.  Note: surprisingly it is not quicker 
    to render directly into a QImage probably due to the CPU cache, 
    it's also useless wrt (writing?) to other colour spaces  */
    
// too confusing - easier to use variables with color names
#if 0
    uchar *ptr0 = lay->channelMem(2, tileNo, 0, 0); // blue
    uchar *ptr1 = lay->channelMem(1, tileNo, 0, 0); // green
    uchar *ptr2 = lay->channelMem(0, tileNo, 0, 0); // red
#endif

    uchar *ptrBlue  = lay->channelMem(2, tileNo, 0, 0); // blue
    uchar *ptrGreen = lay->channelMem(1, tileNo, 0, 0); // green
    uchar *ptrRed   = lay->channelMem(0, tileNo, 0, 0); // red
    uchar *ptrAlpha = 0;
    
    if (m_cMode == cm_RGBA)    
         ptrAlpha = lay->channelMem(3, tileNo, 0, 0); // alpha
        
    for(int y = 0; y < TILE_SIZE; y++)
    {
// this directly equates what is in each channel to a QImage scanline
// offset backwards to front which hardcodes it to littlendian architecture
#if 0
        uchar *ptr = m_img.scanLine(y);
	    for(int x = TILE_SIZE; x; x--)
	    {
	        *ptr++ = *ptr0++; // blue
	        *ptr++ = *ptr1++; // green
	        *ptr++ = *ptr2++; // red
	        ptr++;  // alpha - ptr incremented, but value not used here
	    }
#endif

// this may be somewhat more inefficient for littlendian systems but 
// should also work with bigendian. It lets Qt determine the color values
// for each channel which automatically takes into account endianness for
// 32 bit images like these.  The intermediate variable can be removed
// later with the pointer increment taking place inside the qRgb( )
// phrase, I think, achieving the same performance.

        uchar iblue, ired, igreen, ialpha;
        
        uint *ptr = (uint *)m_img.scanLine(y);
	    for(int x = TILE_SIZE; x; x--)
	    {
            iblue   = *ptrBlue++;
            igreen  = *ptrGreen++;
            ired    = *ptrRed++;
                       
            if (m_cMode == cm_RGBA)
            {
                ialpha  = *ptrAlpha++;          

                // note - to duplicate (sortof) bigendian bug on littleendian
                // system, comment out next line and uncomment out the
                // one after - for testing only - john
                *ptr = qRgba(ired, igreen, iblue, ialpha);
                //*ptr = qRgb(ired, igreen, 255 - ialpha);
            }    
            else
            {    
                *ptr = qRgb(ired, igreen, iblue);
            }    
                
            ptr++; 
	    }
    }

    // Construct the relevant pixmap
    convertImageToPixmap(&m_img, pix);
}