doc/indevs: add some XCB info to x11grab

Signed-off-by: Lou Logan <lou@lrcd.com>

doc/indevs.texi

@@ -975,8 +975,12 @@ other filename will be interpreted as device number 0.
 
 X11 video input device.
 
-Depends on X11, Xext, and Xfixes. Requires the configure option
-@code{--enable-x11grab}.
+To enable this input device during configuration you need libxcb
+installed on your system. It will be automatically detected during
+configuration.
+
+Alternatively, the configure option @option{--enable-x11grab} exists
+for legacy Xlib users.
 
 This device allows one to capture a region of an X11 display.
 
@@ -994,10 +998,12 @@ omitted, and defaults to "localhost". The environment variable
 area with respect to the top-left border of the X11 screen. They
 default to 0.
 
-Check the X11 documentation (e.g. man X) for more detailed information.
+Check the X11 documentation (e.g. @command{man X}) for more detailed
+information.
 
-Use the @command{dpyinfo} program for getting basic information about the
-properties of your X11 display (e.g. grep for "name" or "dimensions").
+Use the @command{xdpyinfo} program for getting basic information about
+the properties of your X11 display (e.g. grep for "name" or
+"dimensions").
 
 For example to grab from @file{:0.0} using @command{ffmpeg}:
 @example
@@ -1046,6 +1052,10 @@ If @var{show_region} is specified with @code{1}, then the grabbing
 region will be indicated on screen. With this option, it is easy to
 know what is being grabbed if only a portion of the screen is grabbed.
 
+@item region_border
+Set the region border thickness if @option{-show_region 1} is used.
+Range is 1 to 128 and default is 3 (XCB-based x11grab only).
+
 For example:
 @example
 ffmpeg -f x11grab -show_region 1 -framerate 25 -video_size cif -i :0.0+10,20 out.mpg
@@ -1061,7 +1071,8 @@ Set the video frame size. Default value is @code{vga}.
 
 @item use_shm
 Use the MIT-SHM extension for shared memory. Default value is @code{1}.
-It may be necessary to disable it for remote displays.
+It may be necessary to disable it for remote displays (legacy x11grab
+only).
 @end table
 
 @section decklink