Need a reference to X protocol documentation for shapemask in transparent xpm

Alan Coopersmith alan.coopersmith at
Mon Oct 28 16:47:03 CET 2013

The X protocol specifications are posted to:

The protocol itself does not cover XPM's, but requires clients to translate
images from whatever format they are stored in to the server's raw image data
format (the "picture rgb" as you call it).

If using the core protocol, "transparency" in images is indeed done with a 1
bit mask.   The Render extension to the protocol allows storing translucency
information as an alpha channel in the image itself.

I don't know why you'd see the picture rgb data twice - that seems like a bug
in the software sending the data to the server.

	-Alan Coopersmith-              alan.coopersmith at
	 Oracle Solaris Engineering -

On 10/28/13 03:24 AM, Michael Enke wrote:
> Hi all,
> I want to know how transparent xpm's are exchanged between X Client and
> Server.
> What I've seen coming over the wire is:
> a: The picture rgb
> b: The shape mask
> c: The picture rgb again.
> 1: Wonder that the shape mask uses width / 2 bytes per row, means width
> * 4 bits per row
>      even the shapemask information is stored only in width * 1 bits per
> row and the rest is discarded.
> 2: Why the rgb is transferred twice (a-b-c) and not only b-c or a-b?
> Where I can find this in the protocol or library specifications?
> Thank you,
> Michael
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