Asus VivoBook S15 S532FA (2020)
Using the Screenpad

For a multi-head configuration, the first requirement is multiple monitors. On the VivoBook the main display is a standard display panel on output eDP1, whose natural size is 1920x1080px and refresh rate 60Hz. The ScreenPad is on output HDMI1, of natural size 1080x2160px and refresh rate 50Hz. There is also a mode of 504x1000px but the screen was black when I tried it. These parameters can be discovered in /var/log/Xorg.log when the defaultly configured X-Server starts up.

The X-Server can (and normally does) handle non-configured monitors as well as hotplugged monitors. I created a file /etc/X11/xorg.conf.d/91-2head.J.conf to configure these monitors, but I need to see if it is actually needed for the XFCE configuration explained here. Here is the configuration fragment:

Section "Monitor"
    Identifier "eDP1"
    Option "Primary" "true"
    Option "PreferredMode" "1920x1080"
    Option "Position" "0 0"
EndSection
Section "Monitor"
    Identifier "HDMI1"
    Option "PreferredMode" "1080x2160"
    Option "Position" "1920 0"
    Option "Rotate" "Right"
EndSection

Section "Device"
    Identifier "Intel"
    Driver "intel"
    Option "Monitor-eDP1" "eDP1"
    Option "Monitor-HDMI1" "HDMI1"
EndSection

Section "Screen"
    Identifier "Screen0"
    Device "Intel"
    Monitor "eDP1"
    # SubSection "Display" , let it figure out the framebuffer geometry.
EndSection

Section "Screen"
    Identifier "Screen1"
    Device "Intel"
    Monitor "HDMI1"
    # SubSection "Display" , let it figure out the framebuffer geometry.
EndSection

Section "ServerLayout"
    Identifier   "2head"
    Screen       0 "Screen0"
    Screen       1 "Screen1" below "Screen0"
EndSection

This configuration has both monitors showing part of one big framebuffer. Most documentation, and the XFCE configuration plugin, assume this arrangement. Windows can be moved freely between the monitors, or even split between them. But it is also possible to create two independent screens.

With this configuration fragment, when the Display Manager (lightdm for me) logs in its greeter, the greeter window will appear on the window where the cursor is, which in my case is always the ScreenPad. It's easier to use the greeter when it's on the main screen, so move the cursor there. [Update: with a side by side layout the greeter gets on the main screen.]

Now you need to tell XFCE to take control of the server layout. Start up the Display settings plugin.

• On the General tab, for each screen (selected in the topmost dropdown list, or by clicking in one screen in the layout map), turn it on with the on-off slider near the dropdown list.
• The main screen, which it calls Laptop, should be the primary display; turn that on.
• The ScreenPad (called Toshiba…) needs to be rotated to the right. Keep the defaults for Resolution, Scale, Refresh, Rotation and Reflection, on both screens.
• Hit Apply, and confirm that the configuration is satisfactory; if it isn't, e.g. if everything goes black, the widget will revert in a few seconds.
• On the Advanced tab I told it to configure new displays when connected, but made no other changes.
• If the default layout is inconvenient, drag the non-primary screen in the layout map. For my purpose the ScreenPad belongs below the main screen. The X-Server configuration fragment shown above sets this up, but the unconfigured default is going to need tweaking. [Update: side by side worked out much better.]

Now the ScreenPad is active but has no content; it's black. Try moving a window off the bottom of the main display: it appears on the ScreenPad.

I would like a non-black background on the ScreenPad. Run the Desktop settings plugin. Move it onto the display you want to configure (the ScreenPad). Get out your magnifying glass. In the Folder dropdown list, pick the directory containing your background image(s). The images' thumbnails will appear in the big Wallpaper area. Click on one; it will be shown in the background. Set the display style. Turn on Apply to all workspaces; it looks like you could potentially have a different background on each workspace.

I kept the defaults on the Menu tab. On the Icons tab, these refer to 128px icons for launching the file browser (Thunar) on your home directory, the global filesytem, or the trash. As an old troglodyte from when Project Athena was new, I never use these, so I turned them off, keeping only the removeable device option.

I did an impromptu power measurement: with the ScreenPad disabled, the laptop draws 8W; enabled it needs 9W, the same power whether the background is black, white, or a photo. So the ScreenPad is a light-valve display (same as the main screen) and it's using 1W to 2W.

Effect of various disruptive events on the screen layout:

• Log out and log in again: This devolved into two days of chaos. I was unable to log in because of a leftover GPG agent, which could neither be re-used nor ignored. Once I got on, my XFCE configuration was trashed by a malevolent entity from the Eich. I'm pretty sure that neither had anything to do with the multihead display.
• Log out and log in again (with the ScreenPad below the main screen): the Panel appears on the ScreenPad. Not good.
• Log out and log in again (with the ScreenPad above the main screen): the Panel is still on the ScreenPad.
• Log out and log in again (with the ScreenPad right of the main screen): Now the Panel is in its proper place on the main screen. The only objection is that the workspace switcher is ultra-wide. With the vertical stacking it was tall and skinny with the window images very small.
• Now re-configuring the background on the ScreenPad, which was lost in the chaos. The best one is ~/Xfiles/jaguar-wide.jpeg in Stretched mode. This is 800x600px designed to be anamorphically expanded to 1920x1080px. (But the ScreenPad is 2160x1080px.) Scaled expands isomorphically to fill the narrower dimension, centered in black borders. Zoomed expands isomorphically to fill the wider dimension, with parts chopped off in the narrow direction.
• Close the lid to suspend, then open the lid to wake up. The result was not perfect but was better than other people report. The main screen came back correctly oriented and populated. The ScreenPad lost its rotation (resulting in a bizarrely squished and stretched picture). But the Display settings widget started automatically and let me restore the configuration. Weird!

So I think the ScreenPad is now operational. Now I need to figure out how to make it useful beyond just showing a pretty picture.