scripts/dpi: Clean-up, improvements and shellcheck-compliant

Fix all shellcheck warnings, mostly by adding double quotes around vars.
Re-order operations and run multiple jobs in parallel to speed up DPI
change speed.
Remove all use of bc, simple sh integer division is sufficient in all
cases.

Signed-off-by: Joe Groocock <me@frebib.net>

scripts/dpi

@@ -1,7 +1,8 @@
 #!/bin/sh
-set -e
+set -eu
 
 # Based on https://github.com/vincentbernat/awesome-configuration/blob/master/bin/xsettingsd-setup
+CONF_DIR="${XDG_CONFIG_HOME:-$HOME/.config}"
 
 dpi=$1
 
@@ -10,27 +11,32 @@ if [ -z "$1" ]; then
     exit 1
 fi
 
-CONF_DIR="${XDG_CONFIG_HOME:-$HOME/.config}/xsettingsd"
-mkdir -p "$CONF_DIR"
+# Update picom and xorg
+sed -i "s/strength =.*$/strength = $(( dpi*8/96 ));/" "$CONF_DIR/picom/picom.conf" &
+xrandr --dpi "$dpi" &
 
-cursor=$(echo $dpi/6 | bc | cut -d. -f1)
+scale=$(( dpi/96 ))
+cursor=$(( dpi/6 ))
 
-# Build xsettingsd.local
+# Build xsettingsd.conf
+mkdir -p "$CONF_DIR/xsettingsd"
 {
-    cat $CONF_DIR/xsettingsd.conf 2>/dev/null || true
-    echo Xcursor/size $cursor
-    echo Gtk/CursorThemeSize $cursor
-    echo Xft/DPI $(( dpi*1024 ))
-    echo Gdk/WindowScalingFactor $(( dpi/96 ))
-    echo Gdk/UnscaledDPI $(( dpi*1024/(dpi/96) ))
-} > $CONF_DIR/xsettingsd.local
+    cat "$CONF_DIR/xsettingsd.local" 2>/dev/null || true
+    echo "Xcursor/size $cursor"
+    echo "Gtk/CursorThemeSize $cursor"
+    echo "Xft/DPI $(( dpi*1024 ))"
+    echo "Gdk/WindowScalingFactor $scale"
+    echo "Gdk/UnscaledDPI $(( dpi*1024/scale ))"
+} > "$CONF_DIR/xsettingsd/xsettingsd.conf"
 
 {
-    echo Xft.dpi: $dpi
-    echo Xcursor.size: $cursor
-} | xrdb -merge
+    echo "Xft.dpi: $dpi"
+    echo "Xcursor.size: $cursor"
+} | xrdb -merge &
 
-xrandr --dpi $dpi
+systemctl --user reload-or-restart xsettingsd &
+wait
 
-systemctl --user reload-or-restart xsettingsd
-systemctl --user --no-block reload i3 polybar@i3bar
+systemctl --user reload \
+    i3 \
+    polybar@i3bar