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>

doc/ffmpeg.texi

@@ -900,8 +900,21 @@ the DISPLAY environment variable.
 ffmpeg -f x11grab -s cif -r 25 -i :0.0+10,20 /tmp/out.mpg
 @end example
 
-0.0 is display.screen number of your X11 server, same as the DISPLAY environment
-variable. 10 is the x-offset and 20 the y-offset for the grabbing.
+10 is the x-offset and 20 the y-offset for the grabbing.
+
+@example
+ffmpeg -f x11grab -follow_mouse centered -s cif -r 25 -i :0.0 /tmp/out.mpg
+@end example
+
+The grabbing region follows the mouse pointer, which stays at the center of
+region.
+
+@example
+ffmpeg -f x11grab -follow_mouse 100 -s cif -r 25 -i :0.0 /tmp/out.mpg
+@end example
+
+Only follows when mouse pointer reaches within 100 pixels to the edge of
+region.
 
 @section Video and Audio file format conversion
 

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

libavdevice/x11grab.c

@@ -71,6 +71,7 @@ struct x11_grab
     int use_shm;             /**< !0 when using XShm extension */
     XShmSegmentInfo shminfo; /**< When using XShm, keeps track of XShm infos */
     int  draw_mouse;         /**< Set by a private option. */
+    int  follow_mouse;       /**< Set by a private option. */
     char *framerate;         /**< Set by a private option. */
 };
 
@@ -95,6 +96,7 @@ x11grab_read_header(AVFormatContext *s1, AVFormatParameters *ap)
     XImage *image;
     int x_off = 0;
     int y_off = 0;
+    int screen;
     int use_shm;
     char *param, *offset;
     int ret = 0;
@@ -141,6 +143,22 @@ x11grab_read_header(AVFormatContext *s1, AVFormatParameters *ap)
     }
     av_set_pts_info(st, 64, 1, 1000000); /* 64 bits pts in us */
 
+    screen = DefaultScreen(dpy);
+
+    if (x11grab->follow_mouse) {
+        int screen_w, screen_h;
+        Window w;
+
+        screen_w = DisplayWidth(dpy, screen);
+        screen_h = DisplayHeight(dpy, screen);
+        XQueryPointer(dpy, RootWindow(dpy, screen), &w, &w, &x_off, &y_off, &ret, &ret, &ret);
+        x_off -= x11grab->width / 2;
+        y_off -= x11grab->height / 2;
+        x_off = FFMIN(FFMAX(x_off, 0), screen_w - x11grab->width);
+        y_off = FFMIN(FFMAX(y_off, 0), screen_h - x11grab->height);
+        av_log(s1, AV_LOG_INFO, "followmouse is enabled, resetting grabbing region to x: %d y: %d\n", x_off, y_off);
+    }
+
     use_shm = XShmQueryExtension(dpy);
     av_log(s1, AV_LOG_INFO, "shared memory extension %s found\n", use_shm ? "" : "not");
 
@@ -171,7 +189,7 @@ x11grab_read_header(AVFormatContext *s1, AVFormatParameters *ap)
             goto out;
         }
     } else {
-        image = XGetImage(dpy, RootWindow(dpy, DefaultScreen(dpy)),
+        image = XGetImage(dpy, RootWindow(dpy, screen),
                           x_off,y_off,
                           x11grab->width, x11grab->height,
                           AllPlanes, ZPixmap);
@@ -374,6 +392,10 @@ x11grab_read_packet(AVFormatContext *s1, AVPacket *pkt)
     int x_off = s->x_off;
     int y_off = s->y_off;
 
+    int screen;
+    Window root;
+    int follow_mouse = s->follow_mouse;
+
     int64_t curtime, delay;
     struct timespec ts;
 
@@ -400,12 +422,43 @@ x11grab_read_packet(AVFormatContext *s1, AVPacket *pkt)
     pkt->size = s->frame_size;
     pkt->pts = curtime;
 
+    screen = DefaultScreen(dpy);
+    root = RootWindow(dpy, screen);
+    if (follow_mouse) {
+        int screen_w, screen_h;
+        int pointer_x, pointer_y, _;
+        Window w;
+
+        screen_w = DisplayWidth(dpy, screen);
+        screen_h = DisplayHeight(dpy, screen);
+        XQueryPointer(dpy, root, &w, &w, &pointer_x, &pointer_y, &_, &_, &_);
+        if (follow_mouse == -1) {
+            // follow the mouse, put it at center of grabbing region
+            x_off += pointer_x - s->width  / 2 - x_off;
+            y_off += pointer_y - s->height / 2 - y_off;
+        } else {
+            // follow the mouse, but only move the grabbing region when mouse
+            // reaches within certain pixels to the edge.
+            if (pointer_x > x_off + s->width - follow_mouse) {
+                x_off += pointer_x - (x_off + s->width - follow_mouse);
+            } else if (pointer_x < x_off + follow_mouse)
+                x_off -= (x_off + follow_mouse) - pointer_x;
+            if (pointer_y > y_off + s->height - follow_mouse) {
+                y_off += pointer_y - (y_off + s->height - follow_mouse);
+            } else if (pointer_y < y_off + follow_mouse)
+                y_off -= (y_off + follow_mouse) - pointer_y;
+        }
+        // adjust grabbing region position if it goes out of screen.
+        s->x_off = x_off = FFMIN(FFMAX(x_off, 0), screen_w - s->width);
+        s->y_off = y_off = FFMIN(FFMAX(y_off, 0), screen_h - s->height);
+    }
+
     if(s->use_shm) {
-        if (!XShmGetImage(dpy, RootWindow(dpy, DefaultScreen(dpy)), image, x_off, y_off, AllPlanes)) {
+        if (!XShmGetImage(dpy, root, image, x_off, y_off, AllPlanes)) {
             av_log (s1, AV_LOG_INFO, "XShmGetImage() failed\n");
         }
     } else {
-        if (!xget_zpixmap(dpy, RootWindow(dpy, DefaultScreen(dpy)), image, x_off, y_off)) {
+        if (!xget_zpixmap(dpy, root, image, x_off, y_off)) {
             av_log (s1, AV_LOG_INFO, "XGetZPixmap() failed\n");
         }
     }
@@ -452,6 +505,9 @@ static const AVOption options[] = {
     { "video_size", "A string describing frame size, such as 640x480 or hd720.", OFFSET(video_size), FF_OPT_TYPE_STRING, {.str = "vga"}, 0, 0, DEC },
     { "framerate", "", OFFSET(framerate), FF_OPT_TYPE_STRING, {.str = "ntsc"}, 0, 0, DEC },
     { "draw_mouse", "Draw the mouse pointer.", OFFSET(draw_mouse), FF_OPT_TYPE_INT, { 1 }, 0, 1, DEC },
+    { "follow_mouse", "Move the grabbing region when the mouse pointer reaches within specified amount of pixels to the edge of region.",
+      OFFSET(follow_mouse), FF_OPT_TYPE_INT, { 0 }, -1, INT_MAX, DEC, "follow_mouse" },
+    { "centered", "Keep the mouse pointer at the center of grabbing region when following.", 0, FF_OPT_TYPE_CONST, { -1 }, INT_MIN, INT_MAX, DEC, "follow_mouse" },
     { NULL },
 };