About xcompmgr

Keith Packard keithp at keithp.com
Sun Mar 14 22:16:59 EET 2004

Around 21 o'clock on Feb 17, Giacomo Di Ciocco wrote:

> I was working on xcompmgr and I was wondering about the range of TRANS_OPACITY 
> and SHADOW_OPACITY, can please someone tell me ?

I'm afraid it's something of a mess right now.  I've got something 
reasonable in my local copy of xcompmgr for these properties, but I've 
broken other stuff so badly that I don't want to commit the changes.

The basic idea is that there is a new _NET_WM window property:


It's a CARD32 property that ranges from 0x00000000 (transparent) through 
0xffffffff (opaque).

For windows which set this property, xcompmgr uses it for the opacity
value.  It has a default policy for windows without this property set;
those which are 'override redirect' get opacity 0xc0000000, otherwise they
are opaque.

It tracks changes to this property, so windows can actually change their 
opacity on the fly.

Window managers need to monitor this property on the application window 
and forward the value to the frame so that xcompmgr can see it.  They are 
also welcome to frob the value themselves if they like.

I've stuck my current xcompmgr.c sources at


I need to add convolution filters to Render so that I can use this version 
of the code and get fuzzy shadows; the sharp shadows are really 


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