What is exactly the relation between wmctrl -d and wmctrl -lG in Unity?

Question

from man wmctrl:

wmctrl is a command that can be used to interact with an X Window manager that is compatible with the EWMH/NetWM specification. wmctrl can query the window manager for information, and it can request that certain window management actions be taken.

The question specifically

The wmctrl -d command can be used to get information about desktops (viewports/workspaces), The wmctrl -lG command lists all windows, including their geometry information.

How can I (in Unity versus other window managers):

• get an overview of the workspaces and how they are arranged?
• find out which is the current workspace?
• find out where a window is located in an absolute sense?
• list windows that are on the current workspace?

from the command line, using these two commands?

Background information

---

The wmctrl -d command
lists desktops. On (e.g.) Xubuntu, when I run wmctrl -d, I can clearly see in the output which is the current workspace, and the screen's resolution (DG) on the workspace(s).

0  - DG: 1024x600  VP: N/A  WA: 0,31 1024x569  1
1  - DG: 1024x600  VP: N/A  WA: 0,31 1024x569  2
2  - DG: 1024x600  VP: N/A  WA: 0,31 1024x569  3
3  * DG: 1024x600  VP: 0,0  WA: 0,31 1024x569  4

The current workspace is marked with a *.

On Unity however, the output of wmctrl -d shows only one (very large) workspace, marked with a *, no matter which is the current "workspace", e.g.:

0  * DG: 3360x2100  VP: 1680,0  WA: 65,24 1615x1026  N/A

---

The wmctrl -lG command
from man wmctrl:
-l: List the windows being managed by the window manager.
-G-: Include geometry information in the output of the -l action

When I run wmctrl -lG on (e.g.) Xubuntu, with a mousepad window on each workspace:

0x03400003  0 241  197  533  244  jacob-1001PX Untitled 1 - Mousepad
0x03400197  1 299  222  533  244  jacob-1001PX Untitled 2 - Mousepad
0x034001be  2 236  201  533  244  jacob-1001PX Untitled 3 - Mousepad
0x034001e3  3 283  228  533  244  jacob-1001PX Untitled 4 - Mousepad

The information is quite understandable; from the second column, we know the workspace the window is on, its position (x,y, column 3/4) and the size (x,y, column 5/6). The position is given in relation to the worspace it is located on.

On Unity however, it is quite a different story. When I have four workspaces and I open a gedit window on every one of them:

0x03c03b81  0 468  -884 875  741  jacob-System-Product-Name Niet-opgeslagen document 1 - gedit
0x03c03e74  0 369  164  1111 741  jacob-System-Product-Name Niet-opgeslagen document 2 - gedit
0x03c03f8e  0 -1269 214  1111 741  jacob-System-Product-Name Niet-opgeslagen document 3 - gedit
0x03c00085  0 -1376 -917 1111 741  jacob-System-Product-Name Niet-opgeslagen document 4 - gedit

Some windows have negative coordinates, some (may) have coordintates that exceed my screen's resolution.

Answer 1

Viewports versus workspaces

As pointed out in this answer, there is an essential difference between Compiz/Unity and other window managers.

If we look at Xubuntu (XFCE), all workspaces are stand alone spaces. All we need to know is the workspace a window is on, and the x and y coordinates. Basically, there is no matrix in which the workspaces are ordered, apart from the "lineair" order 1, 2, 3 etc.

This is different in Unity, where there is actually only one workspace. The (spanning) workspace is divided in a number of sections, called viewports. These viewports are arranged in rows and columns.

That way it is possible that one window is partially visible on all viewports:

unlike workspaces:

Differences in the output of wmctrl -d and how to interpret

To understand the output of wmctrl -lG, we should understand its "anatomy":

1. desktop number (first = 0)
2. current desktop mark ("*" if it is the current desktop (workspace), "-" if not)
3. desktop geometry (the size of the desktop x-y)
4. viewport position (position on the desktop; see Unity)
5. workarea geometry as ("usable" size of the desktop, minus panels etc.; first column is px from left/top)
6. name of the desktop (possibly containing multiple spaces)

Since Unity only has one workspace, the output always shows a * on [2]. How do we know how the viewports are arranged and what is the current viewport?

The information is in VP: 1680,0 ([4]). Not simply as a viewport number, but as an x and y coordinate. These coordinates can be zero or x*the screen's resolution. To know how the viewports are set up, we will need to know the screen's reolution as well (with the help of xrandr).

How to find out:

• how many viewports are there currently and how are they arranged:
  

  Looking at the DG: 3360x2100 in the "Unity" example, and knowing that our screen's resolution is 1680x1050, we can conclude there are two columns of viewports (3360/1680) and two rows (2100/1050).

• which is the current workspace:

  An example
  The screen has a resolution of 1680x1050. The viewport information sais VP: 1680,0. Cordinates are displayed as the left upper corner, So we are on the second column, first row.

• where a window is located in an absolute sense:

  Once we know which viewport is the current one, we can localize the windows, looking at their coordinates in the output of wmctrl -lG [3]:

1. window - id
2. desktop number (on Unity: always 0 as pointed out)
3. window coordinates, from the perspective of the current viewport (x-y)
4. window size, from the perspective of the (w-h)
5. computer name

6. window name

   We can simply locate the window, with the origin at the left top of the current viewport.

   Below an example of a screen resolution of 1680x1050, viewports 2x2:

   window coordinates from the perspective of viewport 1

   

   window coordinates from the perspective of viewport 4

   

   • which are the windows on the current workspace:

   With the information above and the help of wmctrl -lG (the window coordinates, section [3]), quite simple:
   

   if

   1. a window's x-coordinate is between 0 and the screen's (horizontal) resolution, and
   2. a window's y-coordinate is between 0 and the screen's (vertical) resolution

   then a window is located on the current viewport.