X11 backing store
Harold L Hunt II
huntharo@msu.edu
Tue Jul 23 12:27:00 GMT 2002
Hans Werner Strube wrote:
> If X11 graphics programs request backing store, for instance, with
> drawattr.backing_store = Always;
> XChangeWindowAttributes(display, drawable, CWBackingStore, &drawattr);
> this seems to have no effect. The same program works correctly in Solaris
> (SPARC) and IRIX (MIPS).
> The memory of my graphics card (8 MB, Rage Mobility) appears sufficient,
> since the whole screen would only use 2.3 MB with 24 bits/pixel. It would
> be desirable to have this possibility to avoid explicit redrawing after
> a portion of the window has been covered or the window has been iconized
> and reopened.
>
Hans,
The amount of memory on your video card is not relevant. All
Cygwin/XFree86 graphics operations are computed in system memory and
only the resulting pixels are transferred to the screen.
Cygwin/XFree86 has support for backing store, but it is not enabled by
default. You have to pass the ``+bs'' parameter to XWin.exe to enable
backing store support:
XWin +bs
We have not confirmed whether the backing store actually performs to
specification. I just ran XWin with the backing store enabled and xterm
running under the mwm window manager failed to redraw its client area
correctly when I moved one xterm over another xterm. I cannot tell you
if this is a bug with general XFree86 code, with Cygwin-specific XFree86
code, with mwm, or with xterm.
I have seen various posting that seem to indicate that backing store
support is not trusted anymore... perhaps it is no longer being
maintained. It is also possible that I have simply misread or
misremembered things. Maybe backing store support is still fully
maintained and perhaps we are simply not using it correctly.
Harold
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