Okay, if the first two lines are:
BACKEND=“glx”
VSYNC=“opengl-swc”
it crashes/locks
If the first two lines are:
BACKEND=“glx”
VSYNC=none
it crashes/locks
If the first two lines are:
BACKEND=“xrender”
VSYNC=“opengl-swc”
It works. That is to say, transparencies come on at that point, So I am assuming it is working.
The only thing I have not tried is:
BACKEND=“xrender”
VSYNC=none
Will try that now and report back.
Okay, this works also:
BACKEND=“xrender”
VSYNC=none
OK, so basically the software renderer works. And yes, 14.04 is not the test case in after 
so, when I just run compton -c -m 0.8, I am not actually using my gpu hardware to render the screen. But am, instead, just using software? Is that right Martin?
If I install 16.04 in VB with 3d hardware enabled, would I be able to test your script then?
okay, this compton conf works for me, but seems to be using glx. It works with or without the -c and -m switches. But, when I use the switches, they work as well:
backend = "glx";
paint-on-overlay = true;
glx-no-stencil = true;
vsync = "opengl-swc";
# Shadow
shadow = true; # Enabled client-side shadows on windows.
# no-dock-shadow = true; # Avoid drawing shadows on dock/panel windows.
no-dnd-shadow = true; # Don't draw shadows on DND windows.
clear-shadow = true; # Zero the part of the shadow's mask behind the window (experimental).
shadow-radius = 7; # The blur radius for shadows. (default 12)
shadow-offset-x = -7; # The left offset for shadows. (default -15)
shadow-offset-y = -7; # The top offset for shadows. (default -15)
shadow-exclude = [
"n:e:Notification",
"n:e:Docky",
"g:e:Synapse",
"g:e:Conky",
"n:w:*Firefox*",
"n:w:*Chromium*",
"n:w:*dockbarx*",
"class_g ?= 'Cairo-dock'",
"class_g ?= 'Xfce4-notifyd'",
"class_g ?= 'Xfce4-power-manager'"
];
# Opacity
detect-client-opacity = true;
# Fading
fading = true; # Fade windows during opacity changes.
fade-delta = 4; # The time between steps in a fade in milliseconds. (default 10).
fade-in-step = 0.03; # Opacity change between steps while fading in. (default 0.028).
fade-out-step = 0.03; # Opacity change between steps while fading out. (default 0.03).
#no-fading-openclose = true; # Fade windows in/out when opening/closing
# Window type settings
wintypes:
{
tooltip = { fade = true; shadow = false; };
};If you comment clear-shadow does it still work?
Yes, it still works Martin. I also can’t see any actual difference arising from commenting that line out.
There is one problem arising from using that conf, though. When I try to maximise any streaming video such as i-player, youtube etc, it just goes to a blue screen. The audio is still playing, but no picture. It has not locked cos it allows me to use the ESC key to go back to embedded view, where the video has continued playing as normal
And does it work if you include no-dock-shadow?
It does work with that line uncommented, yes. That was the one line I commented when I first used the conf file cos, with it uncommented, it was not showing my panel shadows. It still worked though.
Okay, narrowed down what is causing blue-screen on full-screen streaming vid:
backend = "glx";
paint-on-overlay = true;
glx-no-stencil = true;
vsync = "opengl-swc";
It’s somewhere in those lines because I have run a temporary conf file with just those lines in it and the blue screen problem persists. But, run compton without any conf file and the blue screen problem goes away.
OK, does compton work when you start it with the following. This is a command line invocation, no .conf file 
compton --config /dev/null \
--backend glx \
--vsync opengl-swc \
--paint-on-overlay \
--glx-swap-method undefined \
--glx-no-stencil \
--unredir-if-possible \
--inactive-dim 0.1 \
--inactive-opacity-override \
--mark-wmwin-focused \
-r 7 -o 0.3 -l -7 -t -7 \
-c -C -G -b \
--shadow-exclude "! name~=''" \
--shadow-exclude "name = 'Notification'" \
--shadow-exclude "name = 'Plank'" \
--shadow-exclude "name = 'Docky'" \
--shadow-exclude "name = 'Kupfer'" \
--shadow-exclude "name *= 'compton'" \
--shadow-exclude "class_g = 'Conky'" \
--shadow-exclude "class_g = 'Kupfer'" \
--shadow-exclude "class_g = 'Synapse'" \
--shadow-exclude "class_g ?= 'Notify-osd'" \
--shadow-exclude "class_g ?= 'Cairo-dock'"
If it doesn’t work please try removing --glx-swap-method undefined \. Thanks for your help 
Hi Martin, What do you mean by “command line invocation”? Do you mean I insert each of those lines, above, in turn, in a terminal? Which is fine, I just need to know.
The above can just be pasted into a terminal to start Compton, although a killall compton should be run first.
I pasted it all in, in one go, but only the first line appeared in the terminal as being pasted:
compton --config /dev/null
So, I am unsure if the rest of the block actually pasted in there.
Nevertheless, Compton appears to be working. Whether that is on software or hardware I am unsure.
Does each line need pasting each in turn?
Ooops. I’ve edited the command line and added the missing \ after /dev/null. Please try it again.
Hi Martin.
Tried it with that line included and with it removed:
--glx-swap-method undefined \
Locked both times I’m afraid
Please try with with the ‘unredir’ line removed. Your system can clearly do glx Compton. I just need to find the compatible config
Still locking with the “unredir” line removed I’m afraid. I should also say, thank you very much for this Martin, since it clearly has little relevance post 14.04.