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From: jim@ncd.COM (Jim Fulton)
Newsgroups: comp.windows.x
Subject: Re: XImages
Message-ID: <9012121928.AA08593@hansen.com>
Date: 12 Dec 90 11:28:19 GMT
References: <927@attc.UUCP>
Sender: daemon@athena.mit.edu (Mr Background)
Organization: Network Computing Devices, Mountain View, CA
Lines: 39


    For image bit order, MSBfirst/LSBfirst are crystal clear. But when
    it comes to byte order ...

If it helps, here's a description that I wrote up recently:


Definitions:

        BitmapPad specifies the number of bits to which each glyph scanline
	will be padded.  This value will always be greater than or equal to
	BitmapUnit.

        BitmapUnit specifies the number of bits that should be treated as a
	unit for swapping.

        ImageByteOrder specifies whether the Most- or Least-Significant Byte
	of each bitmap-unit will be returned first.

        BitmapBitOrder specifies whether the left-most bit in each glyph
	bitmap-unit is stored in the Most- or Least-Significant Bit of
	transmitted bitmap-unit.


Algorithm:

        Each scanline is padded to a multiple of the number of bits
        specified by BitmapPad.  The scanline is then
        divided into a sequence of BitmapUnit bits.  The bits of
        each unit are then swapped such that the left-most pixel is
        stored in the most- or least-significant bit, according to
        BitmapBitOrder.  The bytes of each unit are then
        swapped such that the most- or least-significant byte is transmitted
	first, according to ImageByteOrder.


					Jim Fulton
					Network Computing Devices
					jim@ncd.com