EWMH proposal for _NET_WM_WINDOW_OPACITY

[Keith Packard]

Around 13 o'clock on Dec 18, Billy Biggs wrote:

>  My argument is that if I have a window with an alpha channel, and I
> have to multiply that by a constant value before compositing it, why not
> let me divide by 32768 (easy) instead of by 65535 (hard).

Whatever.  It's all done within Render anyways, so all that's necessary is 
to convert the one value to an alpha value inside a Picture.  The main 
reason for just using the whole range of 32-bit values is that there are 
no invalid values this way, so there can't be an error to try and signal.

We could just as easily use an 8 or 16 bit value, but it didn't seem 
useful to permit that.

I guess my main question is whether the specification is clear enough and
whether it fits the style of EWMH.  I think the semantics are reasonable.

-keith