[Gdal-dev] Fix for PNG byte order problems under x86

[Robert Osfield]

Hi,

When working with a 16bit PNG file under x86 I found a problem with the 
endianess, looking into this issue revealled that PNG is stored as the 
network byte order/MSB, whereas x86 is LSB.  The libpng library has a 
png_set_swap() method for forcing a swap, but you have to call it explitily 
to enable it to correct the endianess for you.

In the file frmts/png/pngdataset.cpp I added:

#if CPL_LSB        
    // png are stored as MSB/big endian, so we'll need to swap bytes if on a
    // LSB/little endian machine.
    if (poDS->nBitDepth>8)
        png_set_swap(poDS->hPNG);
#endif

File attached.

Regards,
Robert.



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