[Gambas-user] Desktop Find, embedding multiple instances of VLC... trials, tribulations, and a solution!

[Stephen Bungay]

I was trying (and have now succeeded) to embed VLC into an embedder on a 
form, then dynamically create multiple instances of that form in 
dynamically created multiple panels on a host form, or in laymen's terms 
'play as many videos as I wanted in one containing window'.

To do this I needed to spawn a video player, find it, then embed it. 
Spawning the player is no problem, and finding it should also have been 
easy since I could use the window name. The video player chosen was VLC, 
and after finding out how to uniquely set the title of the VLC window I 
ran headlong into the problem of finding that window by what I assumed 
would be it's unique name under X. This is where the trouble started, 
and I place the blame squarely on the developers of VLC, I hope this 
information helps others.

Lets say we launch VLC from a bash shell with the following;

$ vlc --intf rc --video-title Fred ~/MyVideo.avi

This places the VLC interface into Remote Control mode (--intf rc), 
allowing us to send commands to it by the the console (potentially VERY 
useful) and puts the title 'Fred' at the top of the window. Now in 
another command shell type xprop.

$ xprop

   The mouse cursor will turn to a cross-hair, move it over the VLC 
window and click on it. Have a look at the resulting output... what 
you're to looking for is WM_NAME(STRING) = "VLC media player"

   WM_NAME can be the name of the window (in this case it should be 
'Fred'), but it does not HAVE to be the same as the (visible) window 
name. The good folks who develop VLC decided to keep the value of 
WM_NAME as 'VLC media player' instead of the name that the user (me in 
this case) wanted; as a result Desktop.Find will never locate a window 
called 'Fred' because as far as it is concerned 'Fred' does not exist. 
What to do?

   As it turns out we CAN change the visible title of an X-Window on the 
fly, a little program called 'wmctrl' allows us to rename the window, 
and my first thought was "GREAT! It can set WM_NAME to the value I 
want... problem solved!". Uh... no. It turns out that 'wmctrl' does 
indeed change WM_NAME, but it does not set it to the value you pass 
in... it sets it to nothing, blank, nada, zip, zilch,... bupkus. Great, 
but... YEAH... we can work with this, here's how;

Launch VLC using the shell command, the visible window title doesn't 
matter at this time.
Use desktop.find to locate the window 'VLC media player' and hang onto 
the handle.
Use another shell command to launch wmctrl and change the visible name 
of the VLC window to whatever you desire. THIS WILL BLANK WM_NAME.
Embed the VLC window using the handle we got from desktop.find.

Because VLC will create all future instances of itself with the same 
WM_NAME, the next time you run through the above process (as long as you 
put a second or so delay in between them) you will correctly find the 
next instance created and get a handle on it (sic).