[ZLM] 

The script below was written in October 2002, nowadays I would use [TWAPI] to change the desktop background:

http://twapi.sourceforge.net/ui.html#set_desktop_wallpaper
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This script sets the daily User Friendly strip as my desktop background. 
I post it here because it may be useful to someone. 
It uses [http] to download the image, [Img] to convert the gif to bmp and [ffidl] to call Windows API.

The difficult part was locating the information about the Windows API. 
Please tell me if there is any obvious way to improve this.

Keywords:  Setting Windows Desktop background, SystemParametersInfo , 
SPIF_SENDCHANGE , SPIF_UPDATEINIFILE , SPIF_SENDWININICHANGE

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 package require http
 package require Img
 load ffidl05.dll     
 set target_page "http://www.userfriendly.org" ; # the page to molest
 set gif_image_path "c:\\gif.gif"              ; # download the image here..
 set bmp_image_path "c:\\bmp.bmp"       ; # ... and feed Windows with this

 #Sugar is sweet ...
 proc between { start "and" end "in" text} {
    set string_start  [string first $start $text]
    set string_end    [string first $end $text $string_start]
    set start_removed [string replace [string range $text $string_start $string_end] 0 [expr [string length $start ]-1] ]
    return [string replace $start_removed end end ]
 }
 
 #I'm behind a proxy here, I must configure it...
 http::config -proxyhost 172.29.153.41 -proxyport 8080
 #... now I can get the initial page
 set html [http::data [http::geturl $target_page]]
 #Image size parameters change, get the whole <IMG> first:
 set url [between "<IMG ALT=\"Latest Strip\"" and "</A>" in $html]
 #I only want the image url...
 set url [between "SRC=\"" and "\">" in $url]
 #...and write the image to a file:
 set gif_file [open $gif_image_path w+] 
 http::geturl $url -blocksize 1024 -channel $gif_file
 close $gif_file
 #I have to convert to BMP to be able to use the Windows API call
 set image [image create photo -file $gif_image_path]
 $image write $bmp_image_path -format bmp
 #this fiddles with user32.dll and refreshes the background immediately
 ffidl::callout dll_SystemParametersInfo {int int pointer-utf8 int} int       [ffidl::symbol user32.dll  SystemParametersInfoA]
 dll_SystemParametersInfo 20 0 $bmp_image_path 3
 exit

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as mentioned above, using twapi looks like this...<<br>>
(to have the hostname written to your wallpaper, for example)

  package require twapi
  package require Img
  
  canvas .c
  pack .c
  .c create text 100 100 -text "hostname: [info hostname]"
  update
  [image create photo -data .c] write kal1.gif
  
  set gif_image_path "kal1.gif"
  set bmp_image_path "kal1.bmp"
  
  #I have to convert to BMP to be able to use the Windows API call
  set image [image create photo -file $gif_image_path]
  $image write $bmp_image_path -format bmp
  
  twapi::set_desktop_wallpaper kal1.bmp
  exit

[Category Application] - [Category Desktop]