Update and reorganize documentation

- Convert "Common Tasks" to "How-to Guides"
  (QubesOS/qubes-issues#6694)
- Make title capitalization consistent across docs
- Fix leftover h1 headings
- Reorganize various pages and topics
- Update permalinks to better match titles
- Create redirects for changed permalinks
- Miscellaneous cleanup

QubesOS/qubes-issues#6701

user/advanced-topics/gui-configuration.md

@@ -0,0 +1,58 @@
+---
+lang: en
+layout: doc
+permalink: /doc/gui-configuration/
+ref: 184
+title: GUI Configuration
+---
+
+
+## Video RAM adjustment for high-resolution displays
+
+When a qube starts, a fixed amount of RAM is allocated to the graphics buffer called video RAM.
+This buffer needs to be at least as big as the whole desktop, accounting for all displays that are or will be connected to the machine.
+By default, it is as much as needed for the current display and an additional full HD (FHD) display (1920×1080 8 bit/channel RGBA).
+This logic fails when the machine has primary display in FHD resolution and, after starting some qubes, a 4K display is connected.
+If the buffer is too small, and internal desktop resize fails.
+
+To increase the minimum size of the video RAM buffer:
+
+```sh
+qvm-features dom0 gui-videoram-min $(($WIDTH * $HEIGHT * 4 / 1024))
+qvm-features dom0 gui-videoram-overhead 0
+```
+
+Where `$WIDTH`×`$HEIGHT` is the maximum desktop size that you anticipate needing.
+For example, if you expect to use a 1080p display and a 4k display side-by-side, that is `(1920 + 3840) × 2160 × 4 / 1024 = 48600`, or slightly more than 48 MiB per qube.
+After making these adjustments, the qubes need to be restarted.
+
+In the case of multiple display with different orientations or if you plug/unplug displays, the following code will set correct memory size using xrandr.
+```sh
+qvm-features dom0 gui-videoram-min $(xrandr --verbose | grep "Screen 0" | sed -e 's/.*current //' -e 's/\,.*//' | awk '{print $1*$3*4/1024}')
+```
+
+The amount of memory allocated per qube is the maximum of:
+- `gui-videoram-min`
+- current display + `gui-videoram-overhead`
+
+Default overhead is about 8 MiB, which is enough for a 1080p display (see above).
+So, the `gui-videoram-overhead` zeroing is not strictly necessary; it only avoids allocating memory that will not be used.
+
+You might face issues when playing video, if the video is choppy instead of
+smooth display this could be because the X server doesn't work. You can use the
+Linux terminal (Ctrl-Alt-F2) after starting the virtual machine, login. You can
+look at the Xorg logs file. As an option you can have the below config as
+well present in `/etc/X11/xorg.conf.d/90-intel.conf`, depends on HD graphics
+though -
+
+```bash
+Section "Device"
+        Identifier "Intel Graphics"
+        Driver "intel"
+        Option "TearFree" "true"
+EndSection
+```
+
+## GUI Troubleshooting
+
+See [GUI Troubleshooting](/doc/gui-troubleshooting) for issues relating to the Qubes graphical user interface and how to fix them.