Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!ZERMATT.LCS.MIT.EDU!RWS
From: RWS@ZERMATT.LCS.MIT.EDU (Robert Scheifler)
Newsgroups: comp.windows.x
Subject: Re: Multiple screens and multiple visuals
Message-ID: <19880826215713.0.RWS@KILLINGTON.LCS.MIT.EDU>
Date: 26 Aug 88 21:57:00 GMT
References: <142@masscomp.UUCP>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 35


    Date: 26 Aug 88 14:00:48 GMT
    From: masscomp!black@uunet.uu.net  (Sam Black)

    For example, our 28-plane display supports (basicallly) 4 24-plane DirectColor
    visuals on screen 0 (4 concurrent colormaps), and a a 2-plane StaticGray visual
    on screen 1 to support the 2 overlay planes.  Likewise, our 12-plane display
    supports 1 10-plane PseudoColor visual, 4 8-plane PseudoColor visuals (subsets
    of the 10-plane visual to simulate 4 hardware colormaps), and a 2-plane
    StaticGray visual on screen 1 to support the 2 overlay planes.

You seem to imply that you need a visual per colormap.  Can you explain
this?  Why isn't it sufficient to just provide one visual and multiple
colormaps?

    First of all, it created unnecessary exposure events.  When an overlay window
    gets unmapped, the underlying graphics need not be redrawn.  Implemented as a
    visual, it was forced to be redrawn.

There is no a priori reason I know of why this is required, except perhaps
that the sample server implementation might not provide adequate internal
support.  Can you explain what "forced" means?

    The other problem had to do with overlay planes in general.  Since overlay
    planes always appear OVER the normal graphics, overlay windows always visually
    "obscure" graphics windows, although they may be lower in the stacking order.
    With separate screens, the stacking orders are disjoint, so the input focus
    is screen-dependent.

I'm again confused.  Although overlay planes appear over normal
graphics, if you have per-pixel enable capability you can certainly set
the control planes so that they only appear over when they are actually
higher in the stacking order, and allow the normal graphics to show
through when they are lower.  It requires appropriate hooks in some
server layers, but I don't see why it can't be done.  Can you explain?