[FFmpeg-devel] [PATCH] x11grab: capture a window instead of the whole screen

Andriy Gelman andriy.gelman at gmail.com
Sat Mar 13 07:02:57 EET 2021


On Sun, 28. Feb 10:39, Andriy Gelman wrote:
> On Sun, 28. Feb 13:57, sgerwk-at-aol.com at ffmpeg.org wrote:
> > Hi,
> > 
> > On Sat, 27 Feb 2021, Andriy Gelman wrote:
> > 
> > > On Mon, 22. Feb 17:53, sgerwk-at-aol.com at ffmpeg.org wrote:
> > > > Hi,
> > > > 
> > > > On Sun, 21 Feb 2021, Andriy Gelman wrote:
> > > > > Hi,
> > > > > > Thanks for updating the patch. Sorry for the delay in getting
> > > > you some feedback..
> > > > > > When I tested with -show_mouse 1 -show_region 1 -window_id xx,
> > > > the mouse and
> > > > > border get drawn in the wrong place. There is around (0.6cm error). Can you
> > > > > reproduce?
> > > > >
> > > > 
> > > > I didn't notice the problem because the wm I use places the top-level
> > > > windows in a window of the same size - at position 0,0. Still, I could
> > > > reproduce it by capturing a subwindow.
> > > > 
> > > > The problem was indeed what you suspected: geo->x,geo->y is the position
> > > > inside the parent, but translate includes it already as it is the position
> > > > within the root window.
> > > > 
> > > > > > From e13c1be7abd6989b3ad80fd8086fe6a0819fd810 Mon Sep 17 00:00:00 2001
> > > > > > From: sgerwk <sgerwk at aol.com>
> > > > > > Date: Wed, 10 Feb 2021 17:36:00 +0100
> > > > > > Subject: [PATCH] libavdevice/xcbgrab: option for grabbing a window instead of
> > > > > >  desktop
> > > > > > > > ---
> > > > > >  doc/indevs.texi       | 14 +++++++-
> > > > > >  libavdevice/xcbgrab.c | 79 ++++++++++++++++++++++++++++++++-----------
> > > > > >  2 files changed, 72 insertions(+), 21 deletions(-)
> > > > > > > > diff --git a/doc/indevs.texi b/doc/indevs.texi
> > > > > > index 3924d03..48fd2b1 100644
> > > > > > --- a/doc/indevs.texi
> > > > > > +++ b/doc/indevs.texi
> > > > > > @@ -1564,8 +1564,20 @@ With @var{follow_mouse}:
> > > > > >  ffmpeg -f x11grab -follow_mouse centered -show_region 1 -framerate 25 -video_size cif -i :0.0 out.mpg
> > > > > >  @end example
> > > > > > > > + at item window_id
> > > > > > +Grab this window, instead of the whole screen.
> > > > > > +
> > > > > > +The id of a window can be found by xwininfo(1), possibly with options -tree and
> > > > > > +-root.
> > > > > > +
> > > > > > +If the window is later enlarged, the new area is not recorded. Video ends when
> > > > > > +the window is closed, unmapped (i.e., iconified) or shrunk beyond the video
> > > > > > +size (which defaults to the initial window size).
> > > > > > +
> > > > > > +This option disables options @option{follow_mouse} and @option{select_region}.
> > > > > > +
> > > > > >  @item video_size
> > > > > > -Set the video frame size. Default is the full desktop.
> > > > > > +Set the video frame size. Default is the full desktop or window.
> > > > > > > >  @item grab_x
> > > > > >  @item grab_y
> > > > > > diff --git a/libavdevice/xcbgrab.c b/libavdevice/xcbgrab.c
> > > > > > index be5d5ea..7697090 100644
> > > > > > --- a/libavdevice/xcbgrab.c
> > > > > > +++ b/libavdevice/xcbgrab.c
> > > > > > @@ -60,6 +60,8 @@ typedef struct XCBGrabContext {
> > > > > >      AVRational time_base;
> > > > > >      int64_t frame_duration;
> > > > > > > > +    xcb_window_t window_id;
> > > > > > > +    int win_x, win_y;
> > > > > > The position of the window is always recalculated so I don't
> > > > think win_x and
> > > > > win_y should be part of the of XCBGrabContext.
> > > > >
> > > > 
> > > > Done. Some functions now require win_x and win_y because they no longer
> > > > find them in XCBGrabContext.
> > > > 
> > > > > >      int x, y;
> > > > > >      int width, height;
> > > > > >      int frame_size;
> > > > > > @@ -82,6 +84,7 @@ typedef struct XCBGrabContext {
> > > > > >  #define OFFSET(x) offsetof(XCBGrabContext, x)
> > > > > >  #define D AV_OPT_FLAG_DECODING_PARAM
> > > > > >  static const AVOption options[] = {
> > > > > > +    { "window_id", "Window to capture", OFFSET(window_id), AV_OPT_TYPE_INT, { .i64 = XCB_NONE }, 0, UINT32_MAX, D },
> > > > > >      { "x", "Initial x coordinate.", OFFSET(x), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },
> > > > > >      { "y", "Initial y coordinate.", OFFSET(y), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },
> > > > > >      { "grab_x", "Initial x coordinate.", OFFSET(x), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },
> > > > > > @@ -157,7 +160,7 @@ static int xcbgrab_frame(AVFormatContext *s, AVPacket *pkt)
> > > > > >      XCBGrabContext *c = s->priv_data;
> > > > > >      xcb_get_image_cookie_t iq;
> > > > > >      xcb_get_image_reply_t *img;
> > > > > > -    xcb_drawable_t drawable = c->screen->root;
> > > > > > +    xcb_drawable_t drawable = c->window_id;
> > > > > >      xcb_generic_error_t *e = NULL;
> > > > > >      uint8_t *data;
> > > > > >      int length;
> > > > > > @@ -267,7 +270,7 @@ static int xcbgrab_frame_shm(AVFormatContext *s, AVPacket *pkt)
> > > > > >      XCBGrabContext *c = s->priv_data;
> > > > > >      xcb_shm_get_image_cookie_t iq;
> > > > > >      xcb_shm_get_image_reply_t *img;
> > > > > > -    xcb_drawable_t drawable = c->screen->root;
> > > > > > +    xcb_drawable_t drawable = c->window_id;
> > > > > >      xcb_generic_error_t *e = NULL;
> > > > > >      AVBufferRef *buf;
> > > > > >      xcb_shm_seg_t segment;
> > > > > > @@ -355,17 +358,17 @@ static void xcbgrab_draw_mouse(AVFormatContext *s, AVPacket *pkt,
> > > > > >      cx = ci->x - ci->xhot;
> > > > > >      cy = ci->y - ci->yhot;
> > > > > > > > -    x = FFMAX(cx, gr->x);
> > > > > > -    y = FFMAX(cy, gr->y);
> > > > > > +    x = FFMAX(cx, gr->win_x + gr->x);
> > > > > > +    y = FFMAX(cy, gr->win_y + gr->y);
> > > > > > > > -    w = FFMIN(cx + ci->width,  gr->x + gr->width)  - x;
> > > > > > -    h = FFMIN(cy + ci->height, gr->y + gr->height) - y;
> > > > > > +    w = FFMIN(cx + ci->width,  gr->win_x + gr->x + gr->width)  - x;
> > > > > > +    h = FFMIN(cy + ci->height, gr->win_y + gr->y + gr->height) - y;
> > > > > > > >      c_off = x - cx;
> > > > > > -    i_off = x - gr->x;
> > > > > > +    i_off = x - gr->x - gr->win_x;
> > > > > > > >      cursor += (y - cy) * ci->width;
> > > > > > -    image  += (y - gr->y) * gr->width * stride;
> > > > > > +    image  += (y - gr->y - gr->win_y) * gr->width * stride;
> > > > > > > >      for (y = 0; y < h; y++) {
> > > > > >          cursor += c_off;
> > > > > > @@ -403,8 +406,8 @@ static void xcbgrab_draw_mouse(AVFormatContext *s, AVPacket *pkt,
> > > > > >  static void xcbgrab_update_region(AVFormatContext *s)
> > > > > >  {
> > > > > >      XCBGrabContext *c     = s->priv_data;
> > > > > > -    const uint32_t args[] = { c->x - c->region_border,
> > > > > > -                              c->y - c->region_border };
> > > > > > +    const uint32_t args[] = { c->win_x + c->x - c->region_border,
> > > > > > +                              c->win_y + c->y - c->region_border };
> > > > > > > >      xcb_configure_window(c->conn,
> > > > > >                           c->window,
> > > > > > @@ -417,16 +420,22 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
> > > > > >      XCBGrabContext *c = s->priv_data;
> > > > > >      xcb_query_pointer_cookie_t pc;
> > > > > >      xcb_get_geometry_cookie_t gc;
> > > > > > +    xcb_translate_coordinates_cookie_t tc;
> > > > > >      xcb_query_pointer_reply_t *p  = NULL;
> > > > > >      xcb_get_geometry_reply_t *geo = NULL;
> > > > > > +    xcb_translate_coordinates_reply_t *translate = NULL;
> > > > > >      int ret = 0;
> > > > > >      int64_t pts;
> > > > > > > >      pts = wait_frame(s, pkt);
> > > > > > > > -    if (c->follow_mouse || c->draw_mouse) {
> > > > > > -        pc  = xcb_query_pointer(c->conn, c->screen->root);
> > > > > > -        gc  = xcb_get_geometry(c->conn, c->screen->root);
> > > > > > +    if (c->window_id == c->screen->root) {
> > > > > > +        c->win_x = 0;
> > > > > > +	c->win_y = 0;
> > > > > > +    }
> > > > > > +    if (c->follow_mouse || c->draw_mouse || c->window_id != c->screen->root) {
> > > > > > +        pc  = xcb_query_pointer(c->conn, c->window_id);
> > > > > > +        gc  = xcb_get_geometry(c->conn, c->window_id);
> > > > > >          p   = xcb_query_pointer_reply(c->conn, pc, NULL);
> > > > > >          if (!p) {
> > > > > >              av_log(s, AV_LOG_ERROR, "Failed to query xcb pointer\n");
> > > > > > @@ -438,6 +447,12 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
> > > > > >              free(p);
> > > > > >              return AVERROR_EXTERNAL;
> > > > > >          }
> > > > > > > +        tc = xcb_translate_coordinates(c->conn, c->window_id,
> > > > c->screen->root, geo->x, geo->y);
> > > > > > It would cleaner if you move win_x,win_y calculation to a
> > > > separate if statement.
> > > > > (I don't think you are going to end up reusing geo->x, geo->y anyway because probably
> > > > > that's what causing the mouse/border offset error).
> > > > >
> > > > 
> > > > Actually, this if is executed in the default case because of draw_mouse. But
> > > > still, the code looks better with a separate if, so I did it.
> > > > 
> > > > > > +        translate = xcb_translate_coordinates_reply(c->conn, tc, NULL);
> > > > > > > +        if (!translate)
> > > > > > +            return AVERROR_EXTERNAL;
> > > > > > p and geo need to be freed on this error.
> > > > > You also need free translate when cleaning up at the end of this function.
> > > > 
> > > > Done. I free translate immediately after getting win_x and win_y.
> > > > 
> > > > > > > +        c->win_x = translate->dst_x;
> > > > > > +        c->win_y = translate->dst_y;
> > > > > >      }
> > > > > > > >      if (c->follow_mouse && p->same_screen)
> > > > > > @@ -447,7 +462,7 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
> > > > > >          xcbgrab_update_region(s);
> > > > > > > >  #if CONFIG_LIBXCB_SHM
> > > > > > > -    if (c->has_shm && xcbgrab_frame_shm(s, pkt) < 0) {
> > > > > > +    if (c->has_shm && (ret = xcbgrab_frame_shm(s, pkt)) == AVERROR(ENOMEM)) {
> > > > > >          av_log(s, AV_LOG_WARNING, "Continuing without shared memory.\n");
> > > > > >          c->has_shm = 0;
> > > > > >      }
> > > > > > IMO this should be a separate commit as it changes how EACCESS
> > > > is
> > > > > interpreted even when the new option is not used.
> > > > >
> > > > 
> > > > I now just don't remember why I changed this, so I restored the previous
> > > > condition.
> > > > 
> > > > > > @@ -558,7 +573,9 @@ static int create_stream(AVFormatContext *s)
> > > > > >      XCBGrabContext *c = s->priv_data;
> > > > > >      AVStream *st      = avformat_new_stream(s, NULL);
> > > > > >      xcb_get_geometry_cookie_t gc;
> > > > > > +    xcb_translate_coordinates_cookie_t tc;
> > > > > >      xcb_get_geometry_reply_t *geo;
> > > > > > +    xcb_translate_coordinates_reply_t *translate;
> > > > > >      int64_t frame_size_bits;
> > > > > >      int ret;
> > > > > > > > @@ -571,11 +588,20 @@ static int
> > > > create_stream(AVFormatContext *s)
> > > > > > > >      avpriv_set_pts_info(st, 64, 1, 1000000);
> > > > > > > > -    gc  = xcb_get_geometry(c->conn, c->screen->root);
> > > > > > +    gc  = xcb_get_geometry(c->conn, c->window_id);
> > > > > >      geo = xcb_get_geometry_reply(c->conn, gc, NULL);
> > > > > > -    if (!geo)
> > > > > > +    if (!geo) {
> > > > > > +        av_log(s, AV_LOG_ERROR, "Can't find window '0x%x', aborting.\n", c->window_id);
> > > > > > +        return AVERROR_EXTERNAL;
> > > > > > +    }
> > > > > > +
> > > > > > +    tc = xcb_translate_coordinates(c->conn, c->window_id, c->screen->root, geo->x, geo->y);
> > > > > > +    translate = xcb_translate_coordinates_reply(c->conn, tc, NULL);
> > > > > > > +    if (!translate)
> > > > > >          return AVERROR_EXTERNAL;
> > > > > > error would leak geo.
> > > > > and translate will need to be freed somewhere if there's no error.
> > > > > > > > > +    c->win_x = translate->dst_x;
> > > > > > +    c->win_y = translate->dst_y;
> > > > > >      if (!c->width || !c->height) {
> > > > > >          c->width = geo->width;
> > > > > >          c->height = geo->height;
> > > > > > You calculate win_x/win_y, but it actually doesn't end up being
> > > > used
> > > > > anywhere in xcbgrab_read_header(), and will get recalculated in
> > > > > xcbgrab_read_packet().
> > > > > You probably meant to also update setup_window()?
> > > > >
> > > > 
> > > > This calculation doesn't seem necessary, indeed. I removed it.
> > > > 
> > > > > (btw, currently the border doesn't end being displayed until the first
> > > > > xcbgrab_read_packet() call because there is no xcb_flush(c->conn) after
> > > > > setup_window(s). But it could be added to display the initial border.)
> > > > >
> > > > 
> > > > I guess this should go in a separate commit, as it also affect the case when
> > > > window_id is not set.
> > > > 
> > > > > > > @@ -750,7 +776,7 @@ static int select_region(AVFormatContext
> > > > *s)
> > > > > >              press_position = (xcb_point_t){ press->event_x, press->event_y };
> > > > > >              rectangle.x = press_position.x;
> > > > > >              rectangle.y = press_position.y;
> > > > > > -            xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> > > > > > +            xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
> > > > > >              was_pressed = 1;
> > > > > >              break;
> > > > > >          }
> > > > > > @@ -759,14 +785,14 @@ static int select_region(AVFormatContext *s)
> > > > > >                  xcb_motion_notify_event_t *motion =
> > > > > >                      (xcb_motion_notify_event_t *)event;
> > > > > >                  xcb_point_t cursor_position = { motion->event_x, motion->event_y };
> > > > > > -                xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> > > > > > +                xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
> > > > > >                  rectangle = rectangle_from_corners(&press_position, &cursor_position);
> > > > > > -                xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> > > > > > +                xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
> > > > > >              }
> > > > > >              break;
> > > > > >          }
> > > > > >          case XCB_BUTTON_RELEASE: {
> > > > > > -            xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> > > > > > +            xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
> > > > > >              done = 1;
> > > > > >              break;
> > > > > >          }
> > > > > > @@ -830,6 +856,19 @@ static av_cold int xcbgrab_read_header(AVFormatContext *s)
> > > > > >          return AVERROR(EIO);
> > > > > >      }
> 
> > > 
> > > > > > You disabled select_region() earlier. These changes can be
> > > > skipped then.
> > > > >
> > > 
> > > > 
> > > > I disagree. The captured window is c->window_id now. Even if this part of
> > > > code is currently unreachable if window_id is not the root window,
> > > > a future commit may make it reachable again.
> > > 
> > > The selection rectangle may still be be drawn on root window.
> > > The partial change will make it more confusing in the commit history.
> > > It's better to leave it IMO.
> > 
> > Ok, I removed those changes. But I still believe it's not the best choice to
> > first generalize the grabbed window to be c->window_id but then assume it's
> > c->screen->root_window instead only in this case.
> 
> The two cases are a bit different. One you grabbing the window, the second you
> are drawing a rectangle for the region selection. 
> 
> If I take you previous patch and force it to go into the region selection path,
> the rectangle doesn't get drawn on the non root window. 
> 
> > 
> > > 
> > > > 
> > > > > > > > +    if (c->window_id == XCB_NONE)
> > > > > > +        c->window_id = c->screen->root;
> > > > > > +    else {
> > > > > > +        if (c->select_region) {
> > > > > > +            av_log(s, AV_LOG_WARNING, "select_region ignored with window_id.\n");
> > > > > > +            c->select_region = 0;
> > > > > > +        }
> > > > > > +        if (c->follow_mouse) {
> > > > > > +            av_log(s, AV_LOG_WARNING, "follow_mouse ignored with window_id.\n");
> > > > > > +            c->follow_mouse = 0;
> > > > > > +        }
> > > > > > +    }
> > > > > > +
> > > > > >      if (c->select_region) {
> > > > > >          ret = select_region(s);
> > > > > > Thanks,
> > > > > -- > Andriy
> > > > > _______________________________________________
> > > > > ffmpeg-devel mailing list
> > > > > ffmpeg-devel at ffmpeg.org
> > > > > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> > > > > > To unsubscribe, visit link above, or email
> > > > > ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".
> > > > 
> > > > Thanks!
> > > 
> > > > From 36e6c5a858415106d4d2d9a76fa45cbd59717c77 Mon Sep 17 00:00:00 2001
> > > > From: sgerwk <sgerwk at aol.com>
> > > > Date: Wed, 10 Feb 2021 17:36:00 +0100
> > > > Subject: [PATCH] libavdevice/xcbgrab: option for grabbing a window instead of
> > > >  desktop
> > > 
> > > 
> > > The behavior with -select_region 1 -follow_mouse 1 is not correct now. It will
> > > always reset the origin to 0,0, i.e.
> > > 
> > > ./ffmpeg -show_region 1 select_region 1 -follow_mouse 1 -f x11grab -i :0 -codec:v mpeg2video out.mp4
> > > 
> > 
> > I used the wrong win_x and win_y in xcbgrab_reposition(). I reverted that
> > function to its previous state, which also fixed the problem.
> > 
> > > > 
> > > > ---
> > > >  doc/indevs.texi       | 14 ++++++-
> > > >  libavdevice/xcbgrab.c | 93 +++++++++++++++++++++++++++++++------------
> > > >  2 files changed, 80 insertions(+), 27 deletions(-)
> > > > 
> > > > diff --git a/doc/indevs.texi b/doc/indevs.texi
> > > > index 3924d03..48fd2b1 100644
> > > > --- a/doc/indevs.texi
> > > > +++ b/doc/indevs.texi
> > > > @@ -1564,8 +1564,20 @@ With @var{follow_mouse}:
> > > >  ffmpeg -f x11grab -follow_mouse centered -show_region 1 -framerate 25 -video_size cif -i :0.0 out.mpg
> > > >  @end example
> > > > 
> > > > + at item window_id
> > > > +Grab this window, instead of the whole screen.
> > > > +
> > > > +The id of a window can be found by xwininfo(1), possibly with options -tree and
> > > > +-root.
> > > > +
> > > > +If the window is later enlarged, the new area is not recorded. Video ends when
> > > > +the window is closed, unmapped (i.e., iconified) or shrunk beyond the video
> > > > +size (which defaults to the initial window size).
> > > > +
> > > > +This option disables options @option{follow_mouse} and @option{select_region}.
> > > > +
> > > >  @item video_size
> > > > -Set the video frame size. Default is the full desktop.
> > > > +Set the video frame size. Default is the full desktop or window.
> > > > 
> > > >  @item grab_x
> > > >  @item grab_y
> > > > diff --git a/libavdevice/xcbgrab.c b/libavdevice/xcbgrab.c
> > > > index be5d5ea..ae935ad 100644
> > > > --- a/libavdevice/xcbgrab.c
> > > > +++ b/libavdevice/xcbgrab.c
> > > > @@ -60,6 +60,7 @@ typedef struct XCBGrabContext {
> > > >      AVRational time_base;
> > > >      int64_t frame_duration;
> > > > 
> > > > +    xcb_window_t window_id;
> > > >      int x, y;
> > > >      int width, height;
> > > >      int frame_size;
> > > > @@ -82,6 +83,7 @@ typedef struct XCBGrabContext {
> > > >  #define OFFSET(x) offsetof(XCBGrabContext, x)
> > > >  #define D AV_OPT_FLAG_DECODING_PARAM
> > > >  static const AVOption options[] = {
> > > > +    { "window_id", "Window to capture", OFFSET(window_id), AV_OPT_TYPE_INT, { .i64 = XCB_NONE }, 0, UINT32_MAX, D },
> > > >      { "x", "Initial x coordinate.", OFFSET(x), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },
> > > >      { "y", "Initial y coordinate.", OFFSET(y), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },
> > > >      { "grab_x", "Initial x coordinate.", OFFSET(x), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },
> > > > @@ -108,7 +110,8 @@ static const AVClass xcbgrab_class = {
> > > > 
> > > >  static int xcbgrab_reposition(AVFormatContext *s,
> > > >                                xcb_query_pointer_reply_t *p,
> > > > -                              xcb_get_geometry_reply_t *geo)
> > > > +                              xcb_get_geometry_reply_t *geo,
> > > > +                              int win_x, int win_y)
> > > >  {
> > > >      XCBGrabContext *c = s->priv_data;
> > > >      int x = c->x, y = c->y;
> > > > @@ -118,8 +121,8 @@ static int xcbgrab_reposition(AVFormatContext *s,
> > > >      if (!p || !geo)
> > > >          return AVERROR(EIO);
> > > > 
> > > > -    p_x = p->win_x;
> > > > -    p_y = p->win_y;
> > > > +    p_x = win_x;
> > > > +    p_y = win_y;
> > > > 
> > > >      if (f == FOLLOW_CENTER) {
> > > >          x = p_x - w / 2;
> > > > @@ -157,7 +160,7 @@ static int xcbgrab_frame(AVFormatContext *s, AVPacket *pkt)
> > > >      XCBGrabContext *c = s->priv_data;
> > > >      xcb_get_image_cookie_t iq;
> > > >      xcb_get_image_reply_t *img;
> > > > -    xcb_drawable_t drawable = c->screen->root;
> > > > +    xcb_drawable_t drawable = c->window_id;
> > > >      xcb_generic_error_t *e = NULL;
> > > >      uint8_t *data;
> > > >      int length;
> > > > @@ -267,7 +270,7 @@ static int xcbgrab_frame_shm(AVFormatContext *s, AVPacket *pkt)
> > > >      XCBGrabContext *c = s->priv_data;
> > > >      xcb_shm_get_image_cookie_t iq;
> > > >      xcb_shm_get_image_reply_t *img;
> > > > -    xcb_drawable_t drawable = c->screen->root;
> > > > +    xcb_drawable_t drawable = c->window_id;
> > > >      xcb_generic_error_t *e = NULL;
> > > >      AVBufferRef *buf;
> > > >      xcb_shm_seg_t segment;
> > > > @@ -333,7 +336,8 @@ static int check_xfixes(xcb_connection_t *conn)
> > > > 
> > > >  static void xcbgrab_draw_mouse(AVFormatContext *s, AVPacket *pkt,
> > > >                                 xcb_query_pointer_reply_t *p,
> > > > -                               xcb_get_geometry_reply_t *geo)
> > > > +                               xcb_get_geometry_reply_t *geo,
> > > > +                               int win_x, int win_y)
> > > >  {
> > > >      XCBGrabContext *gr = s->priv_data;
> > > >      uint32_t *cursor;
> > > > @@ -355,17 +359,17 @@ static void xcbgrab_draw_mouse(AVFormatContext *s, AVPacket *pkt,
> > > >      cx = ci->x - ci->xhot;
> > > >      cy = ci->y - ci->yhot;
> > > > 
> > > > -    x = FFMAX(cx, gr->x);
> > > > -    y = FFMAX(cy, gr->y);
> > > > +    x = FFMAX(cx, win_x + gr->x);
> > > > +    y = FFMAX(cy, win_y + gr->y);
> > > > 
> > > > -    w = FFMIN(cx + ci->width,  gr->x + gr->width)  - x;
> > > > -    h = FFMIN(cy + ci->height, gr->y + gr->height) - y;
> > > > +    w = FFMIN(cx + ci->width,  win_x + gr->x + gr->width)  - x;
> > > > +    h = FFMIN(cy + ci->height, win_y + gr->y + gr->height) - y;
> > > > 
> > > >      c_off = x - cx;
> > > > -    i_off = x - gr->x;
> > > > +    i_off = x - gr->x - win_x;
> > > > 
> > > >      cursor += (y - cy) * ci->width;
> > > > -    image  += (y - gr->y) * gr->width * stride;
> > > > +    image  += (y - gr->y - win_y) * gr->width * stride;
> > > > 
> > > >      for (y = 0; y < h; y++) {
> > > >          cursor += c_off;
> > > > @@ -400,11 +404,11 @@ static void xcbgrab_draw_mouse(AVFormatContext *s, AVPacket *pkt,
> > > >  }
> > > >  #endif /* CONFIG_LIBXCB_XFIXES */
> > > > 
> > > > -static void xcbgrab_update_region(AVFormatContext *s)
> > > > +static void xcbgrab_update_region(AVFormatContext *s, int win_x, int win_y)
> > > >  {
> > > >      XCBGrabContext *c     = s->priv_data;
> > > > -    const uint32_t args[] = { c->x - c->region_border,
> > > > -                              c->y - c->region_border };
> > > > +    const uint32_t args[] = { win_x + c->x - c->region_border,
> > > > +                              win_y + c->y - c->region_border };
> > > > 
> > > >      xcb_configure_window(c->conn,
> > > >                           c->window,
> > > > @@ -417,16 +421,23 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
> > > >      XCBGrabContext *c = s->priv_data;
> > > >      xcb_query_pointer_cookie_t pc;
> > > >      xcb_get_geometry_cookie_t gc;
> > > > +    xcb_translate_coordinates_cookie_t tc;
> > > >      xcb_query_pointer_reply_t *p  = NULL;
> > > >      xcb_get_geometry_reply_t *geo = NULL;
> > > > +    xcb_translate_coordinates_reply_t *translate = NULL;
> > > >      int ret = 0;
> > > >      int64_t pts;
> > > > +    int win_x, win_y;
> > > > 
> > > >      pts = wait_frame(s, pkt);
> > > 
> > > > 
> > > > +    if (c->window_id == c->screen->root) {
> > > > +        win_x = 0;
> > > > +        win_y = 0;
> > > > +    }
> > > 
> > > You could zero initialize win_x/win_y and skip this if statement.
> > 
> > Done.
> > 
> > > 
> > > >      if (c->follow_mouse || c->draw_mouse) {
> > > > -        pc  = xcb_query_pointer(c->conn, c->screen->root);
> > > > -        gc  = xcb_get_geometry(c->conn, c->screen->root);
> > > > +        pc  = xcb_query_pointer(c->conn, c->window_id);
> > > > +        gc  = xcb_get_geometry(c->conn, c->window_id);
> > > >          p   = xcb_query_pointer_reply(c->conn, pc, NULL);
> > > >          if (!p) {
> > > >              av_log(s, AV_LOG_ERROR, "Failed to query xcb pointer\n");
> > > > @@ -439,12 +450,27 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
> > > >              return AVERROR_EXTERNAL;
> > > >          }
> > > >      }
> > > > +    if (c->window_id != c->screen->root) {
> > > > +        tc = xcb_translate_coordinates(c->conn, c->window_id, c->screen->root, 0, 0);
> > > > +        translate = xcb_translate_coordinates_reply(c->conn, tc, NULL);
> > > > +        if (!translate) {
> > > 
> > > > +            if (p != NULL)
> > > > +                free(p);
> > > > +            if (geo != NULL)
> > > > +                free(geo);
> > > 
> > > It's fine to parse NULL to free, so the checks are not needed.
> > 
> > Done.
> > 
> > > 
> > > > +            av_log(s, AV_LOG_ERROR, "Failed to translate xcb geometry\n");
> > > > +            return AVERROR_EXTERNAL;
> > > > +        }
> > > > +        win_x = translate->dst_x;
> > > > +        win_y = translate->dst_y;
> > > > +        free(translate);
> > > > +    }
> > > > 
> > > >      if (c->follow_mouse && p->same_screen)
> > > > -        xcbgrab_reposition(s, p, geo);
> > > > +        xcbgrab_reposition(s, p, geo, win_x, win_y);
> > > 
> > > I don't think we should change the xcbgrab_reposition() code. It's not that
> > > useful to follow a mouse region in a window, and it's disabled with your option.
> > > 
> > 
> > Done.
> > 
> > > 
> > > >      if (c->show_region)
> > > > -        xcbgrab_update_region(s);
> > > > +        xcbgrab_update_region(s, win_x, win_y);
> > > > 
> > > >  #if CONFIG_LIBXCB_SHM
> > > >      if (c->has_shm && xcbgrab_frame_shm(s, pkt) < 0) {
> > > > @@ -459,7 +485,7 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
> > > > 
> > > >  #if CONFIG_LIBXCB_XFIXES
> > > >      if (ret >= 0 && c->draw_mouse && p->same_screen)
> > > > -        xcbgrab_draw_mouse(s, pkt, p, geo);
> > > > +        xcbgrab_draw_mouse(s, pkt, p, geo, win_x, win_y);
> > > >  #endif
> > > > 
> > > >      free(p);
> > > > @@ -571,10 +597,12 @@ static int create_stream(AVFormatContext *s)
> > > > 
> > > >      avpriv_set_pts_info(st, 64, 1, 1000000);
> > > > 
> > > > -    gc  = xcb_get_geometry(c->conn, c->screen->root);
> > > > +    gc  = xcb_get_geometry(c->conn, c->window_id);
> > > >      geo = xcb_get_geometry_reply(c->conn, gc, NULL);
> > > > -    if (!geo)
> > > > +    if (!geo) {
> > > > +        av_log(s, AV_LOG_ERROR, "Can't find window '0x%x', aborting.\n", c->window_id);
> > > >          return AVERROR_EXTERNAL;
> > > > +    }
> > > > 
> > > >      if (!c->width || !c->height) {
> > > >          c->width = geo->width;
> > > > @@ -750,7 +778,7 @@ static int select_region(AVFormatContext *s)
> > > >              press_position = (xcb_point_t){ press->event_x, press->event_y };
> > > >              rectangle.x = press_position.x;
> > > >              rectangle.y = press_position.y;
> > > > -            xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> > > > +            xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
> > > >              was_pressed = 1;
> > > >              break;
> > > >          }
> > > > @@ -759,14 +787,14 @@ static int select_region(AVFormatContext *s)
> > > >                  xcb_motion_notify_event_t *motion =
> > > >                      (xcb_motion_notify_event_t *)event;
> > > >                  xcb_point_t cursor_position = { motion->event_x, motion->event_y };
> > > > -                xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> > > > +                xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
> > > >                  rectangle = rectangle_from_corners(&press_position, &cursor_position);
> > > > -                xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> > > > +                xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
> > > >              }
> > > >              break;
> > > >          }
> > > >          case XCB_BUTTON_RELEASE: {
> > > > -            xcb_poly_rectangle(conn, root_window, gc, 1, &rectangle);
> > > > +            xcb_poly_rectangle(conn, c->window_id, gc, 1, &rectangle);
> > > >              done = 1;
> > > >              break;
> > > >          }
> > > > @@ -830,6 +858,19 @@ static av_cold int xcbgrab_read_header(AVFormatContext *s)
> > > >          return AVERROR(EIO);
> > > >      }
> > > > 
> > > > +    if (c->window_id == XCB_NONE)
> > > > +        c->window_id = c->screen->root;
> > > > +    else {
> > > > +        if (c->select_region) {
> > > > +            av_log(s, AV_LOG_WARNING, "select_region ignored with window_id.\n");
> > > > +            c->select_region = 0;
> > > > +        }
> > > > +        if (c->follow_mouse) {
> > > > +            av_log(s, AV_LOG_WARNING, "follow_mouse ignored with window_id.\n");
> > > > +            c->follow_mouse = 0;
> > > > +        }
> > > > +    }
> > > > +
> > > >      if (c->select_region) {
> > > >          ret = select_region(s);
> > > >          if (ret < 0) {
> > > > -- 
> > > > 2.30.1
> > > > 
> > > 
> > > > _______________________________________________
> > > > ffmpeg-devel mailing list
> > > > ffmpeg-devel at ffmpeg.org
> > > > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> > > > 
> > > > To unsubscribe, visit link above, or email
> > > > ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".
> > > 
> > > 
> > > Thanks,
> > > -- 
> > > Andriy
> > > _______________________________________________
> > > ffmpeg-devel mailing list
> > > ffmpeg-devel at ffmpeg.org
> > > https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
> > > 
> > > To unsubscribe, visit link above, or email
> > > ffmpeg-devel-request at ffmpeg.org with subject "unsubscribe".
> 
> > From 1a350c9de2acbf133d62c1eeb6b5e90dd0a5dc9d Mon Sep 17 00:00:00 2001
> > From: sgerwk <sgerwk at aol.com>
> > Date: Wed, 10 Feb 2021 17:36:00 +0100
> > Subject: [PATCH] libavdevice/xcbgrab: option for grabbing a window instead of
> >  desktop
> > 
> > ---
> >  doc/indevs.texi       | 14 ++++++++-
> >  libavdevice/xcbgrab.c | 70 ++++++++++++++++++++++++++++++++-----------
> >  2 files changed, 65 insertions(+), 19 deletions(-)
> > 
> > diff --git a/doc/indevs.texi b/doc/indevs.texi
> > index 3924d03..48fd2b1 100644
> > --- a/doc/indevs.texi
> > +++ b/doc/indevs.texi
> > @@ -1564,8 +1564,20 @@ With @var{follow_mouse}:
> >  ffmpeg -f x11grab -follow_mouse centered -show_region 1 -framerate 25 -video_size cif -i :0.0 out.mpg
> >  @end example
> >  
> > + at item window_id
> > +Grab this window, instead of the whole screen.
> > +
> > +The id of a window can be found by xwininfo(1), possibly with options -tree and
> > +-root.
> > +
> > +If the window is later enlarged, the new area is not recorded. Video ends when
> > +the window is closed, unmapped (i.e., iconified) or shrunk beyond the video
> > +size (which defaults to the initial window size).
> > +
> > +This option disables options @option{follow_mouse} and @option{select_region}.
> > +
> >  @item video_size
> > -Set the video frame size. Default is the full desktop.
> > +Set the video frame size. Default is the full desktop or window.
> >  
> >  @item grab_x
> >  @item grab_y
> > diff --git a/libavdevice/xcbgrab.c b/libavdevice/xcbgrab.c
> > index be5d5ea..956ea32 100644
> > --- a/libavdevice/xcbgrab.c
> > +++ b/libavdevice/xcbgrab.c
> > @@ -60,6 +60,7 @@ typedef struct XCBGrabContext {
> >      AVRational time_base;
> >      int64_t frame_duration;
> >  
> > +    xcb_window_t window_id;
> >      int x, y;
> >      int width, height;
> >      int frame_size;
> > @@ -82,6 +83,7 @@ typedef struct XCBGrabContext {
> >  #define OFFSET(x) offsetof(XCBGrabContext, x)
> >  #define D AV_OPT_FLAG_DECODING_PARAM
> >  static const AVOption options[] = {
> > +    { "window_id", "Window to capture", OFFSET(window_id), AV_OPT_TYPE_INT, { .i64 = XCB_NONE }, 0, UINT32_MAX, D },
> >      { "x", "Initial x coordinate.", OFFSET(x), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },
> >      { "y", "Initial y coordinate.", OFFSET(y), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },
> >      { "grab_x", "Initial x coordinate.", OFFSET(x), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, INT_MAX, D },
> > @@ -157,7 +159,7 @@ static int xcbgrab_frame(AVFormatContext *s, AVPacket *pkt)
> >      XCBGrabContext *c = s->priv_data;
> >      xcb_get_image_cookie_t iq;
> >      xcb_get_image_reply_t *img;
> > -    xcb_drawable_t drawable = c->screen->root;
> > +    xcb_drawable_t drawable = c->window_id;
> >      xcb_generic_error_t *e = NULL;
> >      uint8_t *data;
> >      int length;
> > @@ -267,7 +269,7 @@ static int xcbgrab_frame_shm(AVFormatContext *s, AVPacket *pkt)
> >      XCBGrabContext *c = s->priv_data;
> >      xcb_shm_get_image_cookie_t iq;
> >      xcb_shm_get_image_reply_t *img;
> > -    xcb_drawable_t drawable = c->screen->root;
> > +    xcb_drawable_t drawable = c->window_id;
> >      xcb_generic_error_t *e = NULL;
> >      AVBufferRef *buf;
> >      xcb_shm_seg_t segment;
> > @@ -333,7 +335,8 @@ static int check_xfixes(xcb_connection_t *conn)
> >  
> >  static void xcbgrab_draw_mouse(AVFormatContext *s, AVPacket *pkt,
> >                                 xcb_query_pointer_reply_t *p,
> > -                               xcb_get_geometry_reply_t *geo)
> > +                               xcb_get_geometry_reply_t *geo,
> > +                               int win_x, int win_y)
> >  {
> >      XCBGrabContext *gr = s->priv_data;
> >      uint32_t *cursor;
> > @@ -355,17 +358,17 @@ static void xcbgrab_draw_mouse(AVFormatContext *s, AVPacket *pkt,
> >      cx = ci->x - ci->xhot;
> >      cy = ci->y - ci->yhot;
> >  
> > -    x = FFMAX(cx, gr->x);
> > -    y = FFMAX(cy, gr->y);
> > +    x = FFMAX(cx, win_x + gr->x);
> > +    y = FFMAX(cy, win_y + gr->y);
> >  
> > -    w = FFMIN(cx + ci->width,  gr->x + gr->width)  - x;
> > -    h = FFMIN(cy + ci->height, gr->y + gr->height) - y;
> > +    w = FFMIN(cx + ci->width,  win_x + gr->x + gr->width)  - x;
> > +    h = FFMIN(cy + ci->height, win_y + gr->y + gr->height) - y;
> >  
> >      c_off = x - cx;
> > -    i_off = x - gr->x;
> > +    i_off = x - gr->x - win_x;
> >  
> >      cursor += (y - cy) * ci->width;
> > -    image  += (y - gr->y) * gr->width * stride;
> > +    image  += (y - gr->y - win_y) * gr->width * stride;
> >  
> >      for (y = 0; y < h; y++) {
> >          cursor += c_off;
> > @@ -400,11 +403,11 @@ static void xcbgrab_draw_mouse(AVFormatContext *s, AVPacket *pkt,
> >  }
> >  #endif /* CONFIG_LIBXCB_XFIXES */
> >  
> > -static void xcbgrab_update_region(AVFormatContext *s)
> > +static void xcbgrab_update_region(AVFormatContext *s, int win_x, int win_y)
> >  {
> >      XCBGrabContext *c     = s->priv_data;
> > -    const uint32_t args[] = { c->x - c->region_border,
> > -                              c->y - c->region_border };
> > +    const uint32_t args[] = { win_x + c->x - c->region_border,
> > +                              win_y + c->y - c->region_border };
> >  
> >      xcb_configure_window(c->conn,
> >                           c->window,
> > @@ -417,16 +420,19 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
> >      XCBGrabContext *c = s->priv_data;
> >      xcb_query_pointer_cookie_t pc;
> >      xcb_get_geometry_cookie_t gc;
> > +    xcb_translate_coordinates_cookie_t tc;
> >      xcb_query_pointer_reply_t *p  = NULL;
> >      xcb_get_geometry_reply_t *geo = NULL;
> > +    xcb_translate_coordinates_reply_t *translate = NULL;
> >      int ret = 0;
> >      int64_t pts;
> > +    int win_x = 0, win_y = 0;
> >  
> >      pts = wait_frame(s, pkt);
> >  
> >      if (c->follow_mouse || c->draw_mouse) {
> > -        pc  = xcb_query_pointer(c->conn, c->screen->root);
> > -        gc  = xcb_get_geometry(c->conn, c->screen->root);
> > +        pc  = xcb_query_pointer(c->conn, c->window_id);
> > +        gc  = xcb_get_geometry(c->conn, c->window_id);
> >          p   = xcb_query_pointer_reply(c->conn, pc, NULL);
> >          if (!p) {
> >              av_log(s, AV_LOG_ERROR, "Failed to query xcb pointer\n");
> > @@ -439,12 +445,25 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
> >              return AVERROR_EXTERNAL;
> >          }
> >      }
> > +    if (c->window_id != c->screen->root) {
> > +        tc = xcb_translate_coordinates(c->conn, c->window_id, c->screen->root, 0, 0);
> > +        translate = xcb_translate_coordinates_reply(c->conn, tc, NULL);
> > +        if (!translate) {
> > +            free(p);
> > +            free(geo);
> > +            av_log(s, AV_LOG_ERROR, "Failed to translate xcb geometry\n");
> > +            return AVERROR_EXTERNAL;
> > +        }
> > +        win_x = translate->dst_x;
> > +        win_y = translate->dst_y;
> > +        free(translate);
> > +    }
> >  
> >      if (c->follow_mouse && p->same_screen)
> >          xcbgrab_reposition(s, p, geo);
> >  
> >      if (c->show_region)
> > -        xcbgrab_update_region(s);
> > +        xcbgrab_update_region(s, win_x, win_y);
> >  
> >  #if CONFIG_LIBXCB_SHM
> >      if (c->has_shm && xcbgrab_frame_shm(s, pkt) < 0) {
> > @@ -459,7 +478,7 @@ static int xcbgrab_read_packet(AVFormatContext *s, AVPacket *pkt)
> >  
> >  #if CONFIG_LIBXCB_XFIXES
> >      if (ret >= 0 && c->draw_mouse && p->same_screen)
> > -        xcbgrab_draw_mouse(s, pkt, p, geo);
> > +        xcbgrab_draw_mouse(s, pkt, p, geo, win_x, win_y);
> >  #endif
> >  
> >      free(p);
> > @@ -571,10 +590,12 @@ static int create_stream(AVFormatContext *s)
> >  
> >      avpriv_set_pts_info(st, 64, 1, 1000000);
> >  
> > -    gc  = xcb_get_geometry(c->conn, c->screen->root);
> > +    gc  = xcb_get_geometry(c->conn, c->window_id);
> >      geo = xcb_get_geometry_reply(c->conn, gc, NULL);
> > -    if (!geo)
> > +    if (!geo) {
> > +        av_log(s, AV_LOG_ERROR, "Can't find window '0x%x', aborting.\n", c->window_id);
> >          return AVERROR_EXTERNAL;
> > +    }
> >  
> >      if (!c->width || !c->height) {
> >          c->width = geo->width;
> > @@ -830,6 +851,19 @@ static av_cold int xcbgrab_read_header(AVFormatContext *s)
> >          return AVERROR(EIO);
> >      }
> >  
> > +    if (c->window_id == XCB_NONE)
> > +        c->window_id = c->screen->root;
> > +    else {
> > +        if (c->select_region) {
> > +            av_log(s, AV_LOG_WARNING, "select_region ignored with window_id.\n");
> > +            c->select_region = 0;
> > +        }
> > +        if (c->follow_mouse) {
> > +            av_log(s, AV_LOG_WARNING, "follow_mouse ignored with window_id.\n");
> > +            c->follow_mouse = 0;
> > +        }
> > +    }
> > +
> >      if (c->select_region) {
> >          ret = select_region(s);
> >          if (ret < 0) {
> > -- 
> > 2.30.1
> > 
> 
> Thanks, your latest patch looks ok to me.
> 
> The code in setup_window could be improved to properly draw the bounding box and
> flush the connection, but I can submit a patch for that later. 
> 
> I hope someone else can look over the patch and give a second opinion.
> If no one replies I'll apply the patch in a couple weeks.

ping, will apply on Sunday if no one objects.

-- 
Andriy


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