| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 1628.1 | Backing store is not guaranteed | MELTIN::dick | Gvriel::Schoeller | Wed Oct 25 1989 12:43 | 19 |
| Les,
X11R3 lists backing store as a standard capability. However, not all servers
support it and even if they do they may run out of backing store resources and
refuse the request. Therefore, your customer can not uniformly rely on the
availablity of backing store.
If backing store is refused, your customer can try getting a pixmap and
drawing in that and then setting that pixmap as the background pixmap of the
window.
If the server is unable to create the requested pixmap then you are back
around to handling expose events. What that really means is if you insist
on backing store (and/or pixmap creation) in order for your program to run
at all, you will have a higher probability of failure than if you also
include expose handling has your last chance mechanism.
Dick
|
| 1628.2 | < Only DECstation > | EVTIS2::TISSERAND | Jean-Marc TISSERAND TSC FRANCE | Wed Oct 25 1989 12:58 | 12 |
|
None of the DIGITAL VAXstations running DECwindows V1.0 supports
backing store. Only the DECstation MIT server's windows code includes
conditional support for backing store and save under.
Hope this help.
Jean-Marc.
|
| 1628.3 | | PSW::WINALSKI | Careful with that VAX, Eugene | Thu Oct 26 1989 15:32 | 9 |
| RE: .0
Even on the DECstation, backing store is not guaranteed. That is an intentional
feature of the X protocol. X applications cannot rely on backing store always
being there. They may still be called on at any time to redraw any arbitrary
part of their windows.
--PSW
|
| 1628.4 | | KERNEL::CARLETONL | The Urban Spaceman II | Fri Oct 27 1989 05:27 | 10 |
| Okay,
Backing store is not guaranteed, okay.
But, can the cust avoid the redraw if backing store is available
and given to him? (He is using DECstation)
Les
|
| 1628.5 | You don't get the exposure event ... | DAVIS::peter | | Fri Oct 27 1989 10:41 | 3 |
| If the server does provide backing store, then the application simply
doesn't get the exposure event, so it doesn't have to redraw. Simple, eh?
|
| 1628.6 | | FK::FRED | So sue me. | Fri Oct 27 1989 20:27 | 33 |
| It's a useless feature for an application that *needs* a bitmap backup.
The application must always maintain it's own backing store regardless
of the server ability to do it (!).
Something that I have been talking to the DECwindows/VMS server
developers about is how to make backing-store useful. The idea
is simple:
1) Need to be able to identify the feature availability from the
application program. This is either via a simple extension,
or as part of the vendor information.
2) If backing store is requested as "always", then either:
a) The window cannot be created unless backing store
is available for it.
or
b) There is a way to query after window creation to
determine the status of backing store on the window.
3) If backing store is granted, then it will never be withdrawn
from the window for any reason (i.e. no memory panics on the
backing-store pixmaps).
Since backing-store may show up in the existing VMS servers in the next
year, and since currently #3 is true. Then all that is needed is to
solve #1 or #2. This will "probably" be thru a server extension (yuk)
even if that means I have to write it... XUIS *needs* backing-store.
_Fred
|