X11::Protocol::XSetRoot(3) set root window background


use X11::Protocol::XSetRoot;
X11::Protocol::XSetRoot->set_background (color => 'green');
# or given $X, but which then can't be used any more
(X => $X,
pixmap => $pixmap_xid,
pixmap_allocated_colors => 1);


This module sets the X root window background in the style of the "xsetroot" program.

The simplest use is a named colour interpreted by the server's usual "AllocNamedColor()" or a 1 to 4 digit hex string like ``#RRGGBB'' or ``#RRRRGGGGBBBB''.

                               (color => 'green');
                               (color => '#FF0000'); # red

A pattern can be set with a pixmap. A pixmap the size of the screen can give a full background picture.

    # draw $pixmap with say $X->black_pixel and $X->white_pixel,
    # then set it with
                               (X      => $X,
                                pixmap => $pixmap);

"set_background()" takes ownership of the given $pixmap and frees it with "FreePixmap()" once put into the window background.

Setting the root to a pixmap drawn by a program is the main use for this module. If you just want a solid colour then that can be done easily enough with the actual "xsetroot" program.

Retained Resources

Allocated pixel colours and any "use_esetroot" preserve pixels and pixmap with "SetCloseDownMode('RetainPermanent')" and leave root window properties "_XSETROOT_ID" or "ESETROOT_PMAP_ID" ready to released by "KillClient()" at a future background change.

In these cases the $X connection cannot be used any more since a further background change and consequent "KillClient()" could occur at any time, perhaps immediately.

If a "pixmap" is given then if it contains any allocated pixels ("AllocColor()" etc) then this should be indicated with the "pixmap_allocated_colors" option. (Allocated pixels are noticed automatically for "pixel" and "color" options.)

    # AllocColor colours, draw $pixmap with them, then
                               (X      => $X,
                                pixmap => $pixmap,
                                pixmap_allocated_colors => 1);
    # don't use $X any more

The easiest thing is to close an $X connection immediately after a "set_background()". Perhaps there could be a return value to say whether a retain was done and so the connection cannot be used again. Or perhaps if in the future "X11::Protocol" had an explicit "$X->close()" then that could be done here so a closed connection would indicate it cannot be used further.

If the root visual is static such as "TrueColor" then there's no colour allocation as such ("AllocColor()" is just a lookup). In this case "set_background()" knows there's no need for "RetainPermanent" for colours, only for pixmaps.

If the "color" or "pixel" options are the screen "black_pixel" or "white_pixel" then those pixels exist permanently in the root colormap and "set_background()" knows there's no need for "RetainPermanent". Similarly if the server has the TOG-CUP extension (see X11::Protocol::Ext::TOG_CUP) then any reserved pixels listed there are recognised as permanent.

Virtual Root

"XSetRoot" looks for "__SWM_VROOT" using X11::Protocol::WM "root_to_virtual_root()" and acts on that when applicable. Such a virtual root is used by "amiwm", "swm" and "tvtwm" window managers and the "xscreensaver" program.

Alas the enlightenment window manager uses a background window covering the root window. This stops most root window programs from working, including XSetRoot here.


The "Esetroot" program and various compatible programs such as "fvwm-root" use different properties than "xsetroot". The "Esetroot" method records the root pixmap ready for use by programs such as "Eterm", for example to implement pseudo-transparency ("Eterm --trans", which is what the method was designed for).

The "set_background()" option "use_esetroot" uses the "Esetroot" style rather than the default "xsetroot" style. If this is given with "pixel" or "color" options then "set_background()" makes a 1x1 pixmap to give a solid colour.

"set_background()" always deletes and kills (as appropriate) both the "xsetroot" and "Esetroot" properties since both are superseded by a new background.

For reference, to use "Eterm --trans" (as of its version 0.9.6 March 2011) an "Esetroot" background should be present at "Eterm" startup and should not be removed later (or set to ``None''). It doesn't notice a later "Esetroot" or re-install. In practice this means "Esetroot" before running "Eterm" and then all future background changes in "Esetroot" style.

The advantage of the "Esetroot" method is that the root pixmap is available for client programs to use in creative ways. If the client draws some of the root pixmap as its own background then it can appear semi-transparent without the SHAPE extension, and perhaps do some visual effects like shading or dithering.

For comparison the "xsetroot" style means the root pixmap is not available to client programs and therefore in principle allows the server to apply it to the hardware and never refer to it again. In practice that might not occur, if for example on multiple console ``virtual terminals'' the server must give up the hardware when switched away.


"X11::Protocol::XSetRoot->set_background (key=>value, ...)"
Set the root window background to a pixmap or colour. The key/value parameters are

    X        => X11::Protocol object
    display  => string ":0.0" etc
    screen   => integer, eg. 0
    root     => XID of root window
    color    => string
    pixel    => integer pixel value
    pixmap   => XID of pixmap to display, or "None"
    pixmap_allocated_colors => boolean, default false
    use_esetroot => boolean, default false

The server is given by an "X" connection object, or a "display" name to connect to, or the default is the "DISPLAY" environment variable.

The root window is given by "root" or "screen", or the default is the default screen in $X either per "$X->choose_screen()" or the default from the display name.

The background to show is given by a colour name, pixel value, or pixmap. "color" can be anything understood by the server "AllocNamedColor()", plus 1 to 4 digit hex

    blue              named colours
    #RGB              hex digits

"pixel" is an integer pixel value in the root window colormap. It's automatically recognised as allocated or not (the screen pre-defined black or white and TOG-CUP reserved pixels are permanent and so reckoned not allocated).

"pixmap" is an XID integer. "set_background()" takes ownership of this pixmap and will "FreePixmap()" once installed. ``None'' or 0 means no pixmap, which gives the server's default root background (usually a black and white weave pattern).

"pixmap_allocated_colors" should be true if any of the pixels in "pixmap" were allocated with "AllocColor()" etc, as opposed to just the screen pre-defined black and white pixels (and any TOG-CUP permanent pixels).

"use_esetroot" means use the root window properties in the style of "Esetroot". This allows programs such as "Eterm" to use the root background for ``pseudo-transparency'' or in other creative ways.

When an allocated pixel or a pixmap with allocated pixels is set as the background the "_XSETROOT_ID" mechanism described above means the $X connection could be killed by another "xsetroot" at any time, perhaps immediately, and for that reason $X should not be used any more. The easiest way is to make "set_background()" the last thing done on $X.

Setting an allocated "pixel" or any "pixmap" can only be done on a $X connection as such, not with the "display" option. This is because retaining the colours with the "_XSETROOT_ID" mechanism can only be done from the client connection which created the resources, not a new separate client connection.


For "xsetroot", if colours in the root window background are allocated by "AllocColor()" etc then "_XSETROOT_ID" is a pixmap XID which can be killed by "KillClient()" to free those colours when the root background is replaced. "_XSETROOT_ID" is only a 1x1 dummy pixmap, it's not the actual root background pixmap.
For "Esetroot" style, this is the current root window background pixmap. It might be set by an "Esetroot" which has run and exited, or it might be set by a window manager or similar which is still running.

Client programs can use this to combine the root background into their own window in interesting ways. Listen to "PropertyNotify" on the root window for background changes. Note that since this pixmap belongs to another client it could be freed at any time, so protocol errors when copying or drawing from it should generally be ignored, or cause a fallback to some default.

For "Esetroot" style, this is the same as "_XROOTPMAP_ID" if that pixmap was created by "Esetroot" and saved by "SetCloseDownMode('RetainPermanent')". This should be freed by "KillClient()" if the background is replaced.

The specification <http://www.eterm.org/docs/view.php?doc=ref#trans> advises killing "ESETROOT_PMAP_ID" only when equal to "_XROOTPMAP_ID". Probably it's safer to always kill "ESETROOT_PMAP_ID" if replacing its value, to be sure of not leaking resources. But perhaps if both "ESETROOT_PMAP_ID" and "_XROOTPMAP_ID" exist then they are always equal.


The default X server.


/etc/X11/rgb.txt on the server, being the usual colour names database for the "color" option above.


Copyright 2010, 2011, 2012, 2013 Kevin Ryde

X11-Protocol-Other is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

X11-Protocol-Other is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

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