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

[sgerwk-at-aol . com]

From 0f1a1c46f05def54869ccb58e5d914fa8e0c5d13 Mon Sep 17 00:00:00 2001
From: sgerwk <sge...@aol.com>
Date: Wed, 20 Jan 2021 17:05:48 +0100
Subject: [PATCH] allow x11grab to capture a window instead of the whole screen

---
 doc/indevs.texi       |  3 +++
 libavdevice/xcbgrab.c | 19 ++++++++++++-------
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/doc/indevs.texi b/doc/indevs.texi
index 3924d03..0738919 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -1564,6 +1564,9 @@ 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
 
+@item window_id
+Grab this window, instead of the whole screen.
+
 @item video_size
 Set the video frame size. Default is the full desktop.
 
diff --git a/libavdevice/xcbgrab.c b/libavdevice/xcbgrab.c
index 95bdc8a..6e4ef5d 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 = 0 }, 0, INT_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;
@@ -566,7 +568,7 @@ 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)
         return AVERROR_EXTERNAL;
@@ -745,7 +747,7 @@ 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;
         }
@@ -754,14 +756,14 @@ 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;
         }
@@ -825,6 +827,9 @@ static av_cold int xcbgrab_read_header(AVFormatContext *s)
         return AVERROR(EIO);
     }
 
+    if (c->window_id == 0)
+        c->window_id = c->screen->root;
+
     if (c->select_region) {
         ret = select_region(s);
         if (ret < 0) {
-- 
2.29.2


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