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From: steve@hpcvlx.cv.hp.com (Steve Hiebert)
Newsgroups: comp.sys.hp
Subject: Re: X in overlay planes on HP SRX machines.
Message-ID: <101950069@hpcvlx.cv.hp.com>
Date: 5 Dec 89 23:51:00 GMT
References: <1052@esatst.yc.estec.nl>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 50

> 1) Accelerated graphics using the 98721 cannot be performed within
> an X window.  The suggested solution is to run X in the overlay
> planes, and have the accelerated graphics run in the image planes,
> with a 'transparent' X window suitable placed.  Could some HP person
> tell me if this is likely to change in future releases of the
> system, or is it some restriction due to the hardware involved?

It's a hardware restriction.  When using the accelerator on a
98720/98721 SRX, X cannot control where the drawing takes place.  The
98730/98731 TSRX has hardware clipping support and multiple
accelerators to allow multiple/obscurable/movable/accelerated (MOMA)
windows.

Support for combined image and overlay windows (i.e., multiple visuals
on the same screen) on the TSRX began as of HP-UX 6.5.

> 2) Given 1), I have to ensure that the 'Transparent' colour is
> always available in the colormap for the overlay planes.  How do I
> do this, given that we are running xdm?  I.e.  can I force the
> colormap to contain transparent without changing the colormap from
> within my application.

It's a color just like any other color.  You probably could write a
client that sets its resources to RetainPermanent and allocates
transparent as a read only colormap entry.  If another colormap is
installed, you will most likely lose your transparent color until your
original map is re-installed

> 3) According to the documentation, the colormap for the overlay
> planes only supports the 3 primary and secondary colours, plus black
> & white.  Again, is this a hardware restriction, or is it likely to
> change in future releases?  It would be nice to have softer colours
> available for the windows in the overlay planes, rather than the
> garish ones available now.

Hmm, I would have thought it would be 5 colors + transparent + black +
white.  Is the documentation saying 3 primary + 3 secondary + black +
white?  The overlay planes are 3 bits deep on the SRX which gives the
hardware limit of 8 colors.  The bits do not feed into a lookup table -
they are fed directly to the CRT guns.  We special case the
transparent color (0,0,1) and use it to set the overlays to
subordinate + black (the overlays blend with the image planes when
subordinate).  The thinking was that, given the hardware limits, (0,0,1)
is indistinguishable from (0,0,0) anyway and so could be used to trigger
transparency.

Steve Hiebert
Hewlett-Packard Co.

Disclaimer:  I am speaking for myself and not for Hewlett-Packard Co.