Use printf %q' instead of set -x': debug_run()

`set -x' + setting PS4 was really hackish.
`printf %q' should guarantee the printed command line is properly quoted,
and is equivalent to the command line that's actually run.
Also, the (( verbosity ... )) tests are now only done inside functions.
Also, the _msg() function is changed again to take the same approach as
the new _quote_cmd_line() function does.

ffcast.bash

@@ -27,9 +27,6 @@ declare -a cast_cmdline=(ffmpeg -v 1 -r 25 -- -vcodec libx264 \
 declare -- cast_cmd=${cast_cmdline[0]}
 declare -- region_select_action
 declare -i borderless=1 mod16=0 print_geometry_only=0 verbosity=0
-PS4='debug: command: '  # for set -x
-x='+x'; [[ $- == *x* ]] && x='-x'  # save set -x
-readonly x
 
 #---
 # Functions
@@ -39,7 +36,28 @@ _msg() {
     shift || return 0
     local fmt=$1
     shift || return 0
-    printf -- "$prefix$fmt\n" "$@"
+    printf '%s' "$prefix"
+    printf "$fmt\n" "$@"
+}
+
+_quote_cmd_line() {
+    local prefix=$1
+    shift || return 0
+    local cmd=$1
+    shift || return 0
+    printf '%s' "$prefix"
+    printf '%q' "$cmd"
+    (( $# )) && printf ' %q' "$@"
+    printf '\n'
+}
+
+debug_dryrun() {
+    (( verbosity >=2 )) || return 0
+    _quote_cmd_line 'debug: command: ' "$@"
+} >&2
+
+debug_run() {
+    debug_dryrun "$@" && "$@"
 }
 
 debug() {
@@ -379,13 +397,11 @@ if ! (( h = mod * (h / mod) )); then
     exit 1
 fi
 
-if (( verbosity >= 1 )); then
-    if (( w < w_old )); then
-        verbose 'region: trim width from %d to %d' $w_old $w
-    fi
-    if (( h < h_old )); then
-        verbose 'region: trim height from %d to %d' $h_old $h
-    fi
+if (( w < w_old )); then
+    verbose 'region: trim width from %d to %d' $w_old $w
+fi
+if (( h < h_old )); then
+    verbose 'region: trim height from %d to %d' $h_old $h
 fi
 
 #---
@@ -440,8 +456,6 @@ else  # no '--', then put x11grab options at first
     cast_args=("${x11grab_opts[@]}" "${cast_args[@]}")
 fi
 
-(( verbosity >= 2 )) && set -x
-"${cast_cmd}" "${cast_args[@]}"
-set $x
+debug_run "${cast_cmd}" "${cast_args[@]}"
 
 # vim:ts=4:sw=4:et:cc=80: