HOWTO: (GDM) Show the user wallpaper/background color, while logging in

[kirsis]

EDIT: An improved, multi-user friendly version available on page 3. Clickity:
http://ubuntuforums.org/showthread.p...33#post5427233
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One of my pet peeves with GDM has been that after logging in, it always turns the screen to a certain color (default = light brown, though this can be changed).

I feel that showing the users wallpaper or the users background color, while starting up the session, feels more polished. Here's how to achieve it, if you feel the same way:

1) We need the install the package xloadimage, which contains the app 'xsetbg'

sudo aptitude install xloadimage

2) Create the script that will set the background immediately after entering your username/password:

sudo gedit /etc/gdm/PostLogin/Default

Paste the following code in this file:

#!/bin/sh
#
# Note that output goes into the .xsession-errors file for easy debugging
#
# Extract the wallpaper filename
WALLPAPER="`cat ~/.gconf/desktop/gnome/background/%gconf.xml | sed -n -e 'N
s/^[ \t]*<entry name="picture_filename".*\n[ \t]*<stringvalue>\(.*\)<\/stringvalue>.*$/\1/ip'`"

# Check if the wallpaper file exists. If yes - draw it, if no - use primary background color
if [ -e "$WALLPAPER" ] && [ -f "$WALLPAPER" ] ; then
	xsetbg -onroot "$WALLPAPER"
else
	
	PRIMARY_COLOR="`cat ~/.gconf/desktop/gnome/background/%gconf.xml | sed -n -e 'N
s/^[ \t]*<entry name="primary_color".*\n[ \t]*<stringvalue>\(.*\)<\/stringvalue>.*$/\1/ip'`"
	xsetroot -cursor_name left_ptr -solid "$PRIMARY_COLOR"
fi

exit 0

(P.S. If you have a tiled background, add the '-tile' switch to the line that executes 'xsetbg')

This script will check for a wallpaper setting, and use 'xsetbg' to draw it to the root window. If a wallpaper image does not exist, it will fill the screen with the desktop background color.


Don't forget to make this script executable:

sudo chmod +x /etc/gdm/PostLogin/Default

Now the only step left is to remove the /etc/gdm/PreSession/Default file. This is the file that sets the root window color and it executes after the PostLogin file, so just move it out of the way:

sudo mv -v /etc/gdm/PreSession/Default /etc/gdm/PreSession/Default.bak

There you go. Now while logging in you should be seeing your background color/wallpaper, instead of the gdm background color.

Problems

There are three problems that this script doesn't or can't handle.

1) If you use a gradient as your desktop background, it will not be displayed. The screen will be filled with just one color (the primary color in the gradient)

2) If your wallpaper is scaled to fit, I suggest you resize it so that it matches your desktop as this script will not do that for you. You can, in theory, use the '-background' switch, coupled with '-border black', '-smooth' and (for png's) '-gamma 2.0', but I've found that 'xsetbg' can't properly scale to fit a lot of images (depending on their resolution, it may leave empty vertical/horizontal space at the edges) and the quality of scaled images is sub-par. I suggest you just resize the wallpaper to fit your resolution in GIMP.

3) If you use desktop effects then at one point the desktop might turn black. I haven't figured out yet, how to avoid this.





There you go, I hope this is useful for somebody
(Tested on Hardy Heron, but should work on older versions too.)


Update: Instructions on how to reverse the modifications

If for some reason the script isn't working out for you (due to the black screen problem or for whatever other reason), you can revert the effect with:

sudo rm /etc/gdm/PostLogin/Default
sudo mv /etc/gdm/PreSession/Default.bak /etc/gdm/PreSession/Default

The first line deletes the file that sets the background and the other line restores the original gdm script.

[aashay]

Originally Posted by kirsis Don't forget to make this script executable: sudo chmod +x /etc/gdm/PreSession/Default

Shouldn't this be the PostSession file?

[kirsis]

Damn, ADHD strikes again

The PostLogin/Default file has to be executable, thanks for catching that

[Eclipse.]

I have been looking for something like this for ages.

I even asked for something simliar to be intergrated into gutsy at the time.

Thanks.

[liquid circuit]

Worked perfectly (after I resized my wallpaper to my resolution, as you suggested)!!! I have compiz enabled, and the graphical blinks/redraws are minimal (using a ATI Radeon 9200).

[kirsis]

Glad you like it, guys

The compiz effect differs from PC to PC. For me the screen turns black for a few seconds, but for my buddy, who is also using this trick + compiz, the screen doesn't turn black at any point.

[MeURi]

I'm running Hardy, and I already get this "effect" out of the box, by just setting the login background as my desktop background (speaking of colors)

Instead, following your how-to just gives me a black screen until gnome is fully loaded

Btw: I too noticed that compiz turns the background black, but it happens just sometimes

[kirsis]

Setting the log in screen background to your desktop doesnt work as nicely for multiple users on one computer. This way every user sees his/her wallpaper + you dont have to think about matching gdm themes/backgrounds

It's odd that you got a persistent black screen. Is your desktop background color set to black (if its not using a wallpaper)? It appears to me that xsetbg fails to find your wallpaper and instead sets your desktop to the primary background color.

If your background color is not black, then it must be some external effect, because AFAIK if xsetbg failed, you should be seeing what you always saw before it.


At any rate, you can revert to your previous configuration with:

sudo rm /etc/gdm/PostLogin/Default
sudo mv /etc/gdm/PreSession/Default.bak /etc/gdm/PreSession/Default

[gsiliceo]

Why is this nasty hack needed when in feisty the wallpaper worked right?

[kirsis]

Originally Posted by gsiliceo Why is this nasty hack needed when in feisty the wallpaper worked right?

Well if the wallpaper works just right for you, then why are you in this thread in the first place? Obviously it doesn't work "just right" for everybody.

Worked for me like a dream

Glad to hear that