qmlglsink: Keep old buffers around a bit longer if they were bound by QML

We don't know exactly when QML will stop using them but it should be
safe to unref them after at least 2 more buffers were bound.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/-/merge_requests/1009>

1 files changed, 19 insertions, 0 deletions

diff --git a/ext/qt/gstqsgtexture.cc b/ext/qt/gstqsgtexture.cc
index bfa79cda0..00e2ddad0 100644
--- a/ext/qt/gstqsgtexture.cc
+++ b/ext/qt/gstqsgtexture.cc
@@ -47,6 +47,7 @@ GstQSGTexture::GstQSGTexture ()
 
   gst_video_info_init (&this->v_info);
   this->buffer_ = NULL;
+  this->buffer_was_bound = FALSE;
   this->qt_context_ = NULL;
   this->sync_buffer_ = gst_buffer_new ();
   this->dummy_tex_id_ = 0;
@@ -56,6 +57,7 @@ GstQSGTexture::~GstQSGTexture ()
 {
   gst_buffer_replace (&this->buffer_, NULL);
   gst_buffer_replace (&this->sync_buffer_, NULL);
+  this->buffer_was_bound = FALSE;
   if (this->dummy_tex_id_ && QOpenGLContext::currentContext ()) {
     QOpenGLContext::currentContext ()->functions ()->glDeleteTextures (1,
         &this->dummy_tex_id_);
@@ -80,11 +82,26 @@ GstQSGTexture::setBuffer (GstBuffer * buffer)
   if (!gst_buffer_replace (&this->buffer_, buffer))
     return FALSE;
 
+  this->buffer_was_bound = FALSE;
   this->qt_context_ = gst_gl_context_get_current ();
 
   return TRUE;
 }
 
+/* only called from the streaming thread with scene graph thread blocked */
+GstBuffer *
+GstQSGTexture::getBuffer (gboolean * was_bound)
+{
+  GstBuffer *buffer = NULL;
+
+  if (this->buffer_)
+    buffer = gst_buffer_ref (this->buffer_);
+  if (was_bound)
+    *was_bound = this->buffer_was_bound;
+
+  return buffer;
+}
+
 /* only called from qt's scene graph render thread */
 void
 GstQSGTexture::bind ()
@@ -142,6 +159,8 @@ GstQSGTexture::bind ()
    * to use the dummy texture */
   use_dummy_tex = FALSE;
 
+  this->buffer_was_bound = TRUE;
+
 out:
   if (G_UNLIKELY (use_dummy_tex)) {
     QOpenGLContext *qglcontext = QOpenGLContext::currentContext ();