x11grab: add follow_mouse AVOption.

-follow_mouse centered|PIXELS
  move grabbing region to where mouse pointer at the center; or
  only move when pointer reaches within PIXELS to the edge.

Signed-off-by: Yu-Jie Lin <livibetter@gmail.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>

1 files changed, 21 insertions, 1 deletions

diff --git a/doc/indevs.texi b/doc/indevs.texi
index c5e04b029e..aa001cdb63 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -248,7 +248,27 @@ For example to grab from @file{:0.0} using @file{ffmpeg}:
 ffmpeg -f x11grab -r 25 -s cif -i :0.0 out.mpg
 
 # Grab at position 10,20.
-ffmpeg -f x11grab -25 -s cif -i :0.0+10,20 out.mpg
+ffmpeg -f x11grab -r 25 -s cif -i :0.0+10,20 out.mpg
+@end example
+
+@subsection @var{follow_mouse} AVOption
+
+The syntax is:
+@example
+-follow_mouse centered|@var{PIXELS}
+@end example
+
+When it is specified with "centered", the grabbing region follows the mouse
+pointer and keeps the pointer at the center of region; otherwise, the region
+follows only when the mouse pointer reaches within @var{PIXELS} (greater than
+zero) to the edge of region.
+
+For example:
+@example
+ffmpeg -f x11grab -follow_mouse centered -r 25 -s cif -i :0.0 out.mpg
+
+# Follows only when the mouse pointer reaches within 100 pixels to edge
+ffmpeg -f x11grab -follow_mouse 100 -r 25 -s cif -i :0.0 out.mpg
 @end example
 
 @c man end INPUT DEVICES