gldownload: Fix renegotiation loop

When DMABuf was tried, we would renegotiate back and fourth between
DMABuf and system memory if the export failed. This would happen for
every single frame.

This patch introduces try_dmabuf_exports boolean, which is unset when
an export failed. This boolean is then put back to TRUE when upstream
pushes new caps, or downstream pushes a reconfigure event.

ext/gl/gstgldownloadelement.c

@@ -45,6 +45,8 @@ static gboolean gst_gl_download_element_get_unit_size (GstBaseTransform * trans,
     GstCaps * caps, gsize * size);
 static GstCaps *gst_gl_download_element_transform_caps (GstBaseTransform * bt,
     GstPadDirection direction, GstCaps * caps, GstCaps * filter);
+static GstCaps *gst_gl_download_element_fixate_caps (GstBaseTransform * trans,
+    GstPadDirection direction, GstCaps * caps, GstCaps * othercaps);
 static gboolean gst_gl_download_element_set_caps (GstBaseTransform * bt,
     GstCaps * in_caps, GstCaps * out_caps);
 static GstFlowReturn
@@ -89,12 +91,15 @@ gst_gl_download_element_class_init (GstGLDownloadElementClass * klass)
   bt_class->start = gst_gl_download_element_start;
   bt_class->stop = gst_gl_download_element_stop;
   bt_class->transform_caps = gst_gl_download_element_transform_caps;
+  bt_class->fixate_caps = gst_gl_download_element_fixate_caps;
   bt_class->set_caps = gst_gl_download_element_set_caps;
   bt_class->get_unit_size = gst_gl_download_element_get_unit_size;
   bt_class->prepare_output_buffer =
       gst_gl_download_element_prepare_output_buffer;
   bt_class->transform = gst_gl_download_element_transform;
   bt_class->decide_allocation = gst_gl_download_element_decide_allocation;
+  bt_class->sink_event = gst_gl_download_element_sink_event;
+  bt_class->src_event = gst_gl_download_element_src_event;
 
   bt_class->passthrough_on_same_caps = TRUE;
 
@@ -124,6 +129,7 @@ gst_gl_download_element_start (GstBaseTransform * bt)
   GstGLDownloadElement *dl = GST_GL_DOWNLOAD_ELEMENT (bt);
 
   dl->dmabuf_allocator = gst_dmabuf_allocator_new ();
+  g_atomic_int_set (&dl->try_dmabuf_exports, TRUE);
 #endif
 
   return TRUE;
@@ -158,8 +164,8 @@ gst_gl_download_element_set_caps (GstBaseTransform * bt, GstCaps * in_caps,
   if (gst_caps_features_contains (features, GST_CAPS_FEATURE_MEMORY_GL_MEMORY)) {
     dl->mode = GST_GL_DOWNLOAD_MODE_PASSTHROUGH;
 #if GST_GL_HAVE_PLATFORM_EGL && GST_GL_HAVE_DMABUF
-  } else if (gst_caps_features_contains (features,
+  } else if (g_atomic_int_get (&dl->try_dmabuf_exports) &&
-          GST_CAPS_FEATURE_MEMORY_DMABUF)) {
+      gst_caps_features_contains (features, GST_CAPS_FEATURE_MEMORY_DMABUF)) {
     dl->mode = GST_GL_DOWNLOAD_MODE_DMABUF_EXPORTS;
 #endif
   } else {
@@ -232,6 +238,33 @@ gst_gl_download_element_transform_caps (GstBaseTransform * bt,
   return result;
 }
 
+static GstCaps *
+gst_gl_download_element_fixate_caps (GstBaseTransform * bt,
+    GstPadDirection direction, GstCaps * caps, GstCaps * othercaps)
+{
+#if GST_GL_HAVE_PLATFORM_EGL && GST_GL_HAVE_DMABUF
+  GstGLDownloadElement *dl = GST_GL_DOWNLOAD_ELEMENT (bt);
+
+  /* Remove DMABuf features if try_dmabuf_exports is not set */
+  if (direction == GST_PAD_SINK && !g_atomic_int_get (&dl->try_dmabuf_exports)) {
+    gint i;
+
+    for (i = 0; i < gst_caps_get_size (othercaps); i++) {
+      GstCapsFeatures *features = gst_caps_get_features (othercaps, i);
+
+      if (features && gst_caps_features_contains (features,
+              GST_CAPS_FEATURE_MEMORY_DMABUF)) {
+        caps = gst_caps_make_writable (othercaps);
+        gst_caps_remove_structure (othercaps, i--);
+      }
+    }
+  }
+#endif
+
+  return GST_BASE_TRANSFORM_CLASS (parent_class)->fixate_caps (bt, direction,
+      caps, othercaps);
+}
+
 static gboolean
 gst_gl_download_element_get_unit_size (GstBaseTransform * trans, GstCaps * caps,
     gsize * size)
@@ -453,6 +486,7 @@ gst_gl_download_element_prepare_output_buffer (GstBaseTransform * bt,
       src_caps = gst_caps_make_writable (src_caps);
       features = gst_caps_get_features (src_caps, 0);
       gst_caps_features_remove (features, GST_CAPS_FEATURE_MEMORY_DMABUF);
+      g_atomic_int_set (&dl->try_dmabuf_exports, FALSE);
       dl->mode = GST_GL_DOWNLOAD_MODE_PBO_TRANSFERS;
 
       if (!gst_base_transform_update_src_caps (bt, src_caps)) {
@@ -500,6 +534,30 @@ gst_gl_download_element_decide_allocation (GstBaseTransform * trans,
       query);
 }
 
+static gboolean
+gst_gl_download_element_sink_event (GstBaseTransform * bt, GstEvent * event)
+{
+  GstGLDownloadElement *dl = GST_GL_DOWNLOAD_ELEMENT (bt);
+
+  /* Retry exporting whenever we have new caps from upstream */
+  if (GST_EVENT_TYPE (event) == GST_EVENT_CAPS)
+    g_atomic_int_set (&dl->try_dmabuf_exports, TRUE);
+
+  return GST_BASE_TRANSFORM_CLASS (parent_class)->sink_event (bt, event);
+}
+
+static gboolean
+gst_gl_download_element_src_event (GstBaseTransform * bt, GstEvent * event)
+{
+  GstGLDownloadElement *dl = GST_GL_DOWNLOAD_ELEMENT (bt);
+
+  /* Retry exporting whenever downstream have changed */
+  if (GST_EVENT_TYPE (event) == GST_EVENT_RECONFIGURE)
+    g_atomic_int_set (&dl->try_dmabuf_exports, TRUE);
+
+  return GST_BASE_TRANSFORM_CLASS (parent_class)->src_event (bt, event);
+}
+
 static void
 gst_gl_download_element_finalize (GObject * object)
 {

ext/gl/gstgldownloadelement.h

@@ -51,6 +51,7 @@ struct _GstGLDownloadElement
   GstGLBaseFilter  parent;
 
   GstGlDownloadMode mode;
+  gboolean try_dmabuf_exports;
   GstAllocator * dmabuf_allocator;
   gboolean add_videometa;
 };