Re: XSetBackgroundPixmap question
On Sat, 2012-05-19 at 23:00 +0100, Glynn Clements wrote: I've encountered code which uses a background pixmap to implement a persistent screen, and drawing to the pixmap then calling XClearWindow (without calling XSetWindowBackgroundPixmap in between) results in the updated pixmap contents appearing in the window. So it appears to use reference counting or similar. Any code which does this is being inadvisably friendly with the implementation. From the protocol spec: Subsequent drawing into the background or border pixmap has an undefined effect on the window state. The server might or might not make a copy of the pixmap. The sample implementation (at least at the dix level) has always done the current behaviour of taking a reference on the pixmap, but the sample implementation is not the only X server ever written. - ajax signature.asc Description: This is a digitally signed message part ___ xorg@lists.x.org: X.Org support Archives: http://lists.freedesktop.org/archives/xorg Info: http://lists.x.org/mailman/listinfo/xorg Your subscription address: arch...@mail-archive.com
Re: XSetBackgroundPixmap question
Am 20.05.2012 05:30, schrieb Keith Packard: Glynn Clements gl...@gclements.plus.com writes: That seems to imply that the X server makes a copy of the pixmap data rather than keeping a reference to the original pixmap. However, I don't believe that's how the X.org server actually implements it. No, it keeps a reference, but not through the Pixmap ID, so while the client can destroy the ID, the server holds a reference to the underlying Pixmap structure itself. No copy is made. Hello keith, i am not an X11 expert, and i am not sure that i understand your answer. So far i understand the problem was how to free the old one and the answer is there is no need to free since you should set the pixmap like this: newpm=xcreatepix() XSetWindowBackgroundPixmap(newpm) xfreepixmap(newpm) Is that what you are saying ? re, wh ___ xorg@lists.x.org: X.Org support Archives: http://lists.freedesktop.org/archives/xorg Info: http://lists.x.org/mailman/listinfo/xorg Your subscription address: arch...@mail-archive.com
Re: XSetBackgroundPixmap question
[I presume that you mean XSetWindowBackgroundPixmap; there is no Xlib function named XSetBackgroundPixmap.] James Buren wrote: When using this Xlib function to set a new background pixmap, how does the old one get freed? If I am setting the root window's background pixmap, I don't know how I can get the XID of the old one. If it is a window I created, I can cache it but that seems overkill if I'm just wanting to discard the old one. Can someone direct me to how I am supposed to free the old background pixmap? Thanks. The manual page for XSetWindowBackgroundPixmap says: The XSetWindowBackgroundPixmap function sets the background pixmap of the window to the specified pixmap. The background pixmap can immediately be freed if no further explicit references to it are to be made. That seems to imply that the X server makes a copy of the pixmap data rather than keeping a reference to the original pixmap. However, I don't believe that's how the X.org server actually implements it. I've encountered code which uses a background pixmap to implement a persistent screen, and drawing to the pixmap then calling XClearWindow (without calling XSetWindowBackgroundPixmap in between) results in the updated pixmap contents appearing in the window. So it appears to use reference counting or similar. The combination of the documentation and the observed behaviour implies that the X server *may* copy the pixmap data or it may just keep a reference. Either way, deleting the pixmap after setting it should be fine, but modifying a pixmap which has been used as a background pixmap has undefined behaviour. Regardless of the implementation, there isn't any way to query the current background pixmap. The background_pixmap field in the XSetWindowAttributes structure used by XChangeWindowAttributes isn't present in the XWindowAttributes structure used by XGetWindowAttributes. -- Glynn Clements gl...@gclements.plus.com ___ xorg@lists.x.org: X.Org support Archives: http://lists.freedesktop.org/archives/xorg Info: http://lists.x.org/mailman/listinfo/xorg Your subscription address: arch...@mail-archive.com
Re: XSetBackgroundPixmap question
Wow, that was fast. Thanks. Some other questions I've been having. I've been considering using the XRender extension and I've noticed the documentation is nearly non-existent. What advantages does it offer over older Xlib drawing API? At the very least, it seems to offer more complex graphics operations like scaling and alpha blending. ___ xorg@lists.x.org: X.Org support Archives: http://lists.freedesktop.org/archives/xorg Info: http://lists.x.org/mailman/listinfo/xorg Your subscription address: arch...@mail-archive.com
Re: XSetBackgroundPixmap question
James Buren r...@ymail.com writes: Wow, that was fast. Thanks. Some other questions I've been having. I've been considering using the XRender extension and I've noticed the documentation is nearly non-existent. What advantages does it offer over older Xlib drawing API? At the very least, it seems to offer more complex graphics operations like scaling and alpha blending. You should look at cairo instead -- it nicely wraps the render extension with a pretty postscript-like API. -- keith.pack...@intel.com pgpAzRRJkjwIZ.pgp Description: PGP signature ___ xorg@lists.x.org: X.Org support Archives: http://lists.freedesktop.org/archives/xorg Info: http://lists.x.org/mailman/listinfo/xorg Your subscription address: arch...@mail-archive.com
Re: XSetBackgroundPixmap question
The combination of the documentation and the observed behaviour implies that the X server *may* copy the pixmap data or it may just keep a reference. Either way, deleting the pixmap after setting it should be fine, but modifying a pixmap which has been used as a background pixmap has undefined behaviour. What is undefined behavior? Modifying a pixmap that is still used as a background pixmap, modifying a pixmap that was used as a background pixmap but has since been replaced, or both of these cases? ___ xorg@lists.x.org: X.Org support Archives: http://lists.freedesktop.org/archives/xorg Info: http://lists.x.org/mailman/listinfo/xorg Your subscription address: arch...@mail-archive.com
