[mutter/gnome-41] screen-cast/monitor-stream: Immediately record scanout frames

[Robert Mader <rmader src gnome org>]

commit 67c981585f8292a9d7d2e5ca61ce22d1e685bec4
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Mon Dec 27 15:32:27 2021 -0300

    screen-cast/monitor-stream: Immediately record scanout frames
    
    When the before-paint function is executed, it's only purpose
    is to check if there's any scanout queue, and immediately
    record it if any.
    
    However, since [1], we regressed in this specific case with the
    introduction of an idle callback in the before-paint function.
    The regression only happens when the PipeWire stream is using
    DMA-BUF buffers, and it would operate as follows:
    
     1. In before-paint, when there's a scanout available, we queue
        an idle callback to capture the monitor. The idle callback
        (almost always) executes after the scanout is pulled from
        the stage view
    
     2. meta_screen_cast_stream_src_maybe_record_frame() is called
        by the idle callback. In the DMA-BUF case, it then runs
        meta_screen_cast_monitor_stream_src_record_to_framebuffer()
    
     3. In meta_screen_cast_monitor_stream_src_record_to_framebuffer(),
        because the stage view doesn't have a scanout anymore, it
        ends up calling cogl_blit_framebuffer() with the stage view
        framebuffer. This is the regression bug.
    
    This regression presents itself in the form of the screencast
    stream showing the desktop when there's an unredirected fullscreen
    application window running.
    
    Revert before-paint - and only that - back to immediately capturing
    any available scanout. Only record these frames when the target
    buffer is a DMA-BUF handle. Nothing is captured on before-paint if
    the stream is not using DMA-BUF, since the regular paint routine
    will handle these frames regularly post-paint.
    
    [1] https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1914
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2186>
    
    (cherry picked from commit 77d5c8c928ca07825a6a1b5df207a5bea5468e7e)

 src/backends/meta-screen-cast-monitor-stream-src.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)
---
diff --git a/src/backends/meta-screen-cast-monitor-stream-src.c 
b/src/backends/meta-screen-cast-monitor-stream-src.c
index 82d3862c9a..3075009017 100644
--- a/src/backends/meta-screen-cast-monitor-stream-src.c
+++ b/src/backends/meta-screen-cast-monitor-stream-src.c
@@ -162,6 +162,7 @@ before_stage_painted (MetaStage           *stage,
   MetaScreenCastMonitorStreamSrc *monitor_src =
     META_SCREEN_CAST_MONITOR_STREAM_SRC (user_data);
   MetaScreenCastStreamSrc *src = META_SCREEN_CAST_STREAM_SRC (monitor_src);
+  MetaScreenCastRecordFlag flags;
 
   if (monitor_src->maybe_record_idle_id)
     return;
@@ -169,10 +170,8 @@ before_stage_painted (MetaStage           *stage,
   if (!clutter_stage_view_peek_scanout (view))
     return;
 
-  monitor_src->maybe_record_idle_id = g_idle_add (maybe_record_frame_on_idle,
-                                                  src);
-  g_source_set_name_by_id (monitor_src->maybe_record_idle_id,
-                           "[mutter] maybe_record_frame_on_idle [monitor-src]");
+  flags = META_SCREEN_CAST_RECORD_FLAG_DMABUF_ONLY;
+  meta_screen_cast_stream_src_maybe_record_frame (src, flags);
 }
 
 static MetaBackend *