gstframepositioner: added 'operator' property

The 'operator' property was added to gstframepositioner so that
blending modes in the compositor could be accessed. This was done
by accessing the pad of the compositor class, and referencing the
'operator' property in that pad. Getters and Setters were also
created so that the 'operator' could be accessed by software that
is based on GES, such as Pitivi.

Related to but does not close Issue
https://gitlab.gnome.org/GNOME/pitivi/-/issues/2313

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-editing-services/-/merge_requests/236>

ges/ges-smart-video-mixer.c

@@ -238,7 +238,8 @@ set_pad_properties_from_positioner_meta (GstPad * mixer_pad, GstSample * sample,
   }
 
   g_object_set (mixer_pad, "xpos", meta->posx, "ypos",
-      meta->posy, "width", meta->width, "height", meta->height, NULL);
+      meta->posy, "width", meta->width, "height", meta->height,
+      "operator", meta->operator, NULL);
 }
 
 /****************************************************

ges/ges-video-source.c

@@ -115,7 +115,7 @@ ges_video_source_create_filters (GESVideoSource * self, GPtrArray * elements,
   GESTrackElement *trksrc = GES_TRACK_ELEMENT (self);
   GstElement *positioner, *videoflip, *capsfilter;
   const gchar *positioner_props[]
-  = { "alpha", "posx", "posy", "width", "height", NULL };
+  = { "alpha", "posx", "posy", "width", "height", "operator", NULL };
   const gchar *videoflip_props[] = { "video-direction", NULL };
 
   g_ptr_array_add (elements, gst_element_factory_make ("queue", NULL));

ges/gstframepositioner.c

@@ -26,6 +26,7 @@
 #include <gst/video/video.h>
 
 #include "gstframepositioner.h"
+#include "ges-internal.h"
 
 GST_DEBUG_CATEGORY_STATIC (_framepositioner);
 #undef GST_CAT_DEFAULT
@@ -57,6 +58,7 @@ enum
   PROP_ZORDER,
   PROP_WIDTH,
   PROP_HEIGHT,
+  PROP_OPERATOR,
   PROP_LAST,
 };
 
@@ -79,6 +81,29 @@ GST_STATIC_PAD_TEMPLATE ("sink",
 G_DEFINE_TYPE (GstFramePositioner, gst_frame_positioner,
     GST_TYPE_BASE_TRANSFORM);
 
+static GType
+gst_compositor_operator_get_type_and_default_value (int *default_operator_value)
+{
+  GstElement *compositor =
+      gst_element_factory_create (ges_get_compositor_factory (), NULL);
+
+  GstPad *compositorPad = gst_element_get_request_pad (compositor, "sink_%u");
+
+  GParamSpec *pspec =
+      g_object_class_find_property (G_OBJECT_GET_CLASS (compositorPad),
+      "operator");
+
+  *default_operator_value =
+      g_value_get_enum (g_param_spec_get_default_value (pspec));
+  g_return_val_if_fail (pspec, G_TYPE_NONE);
+
+  gst_element_release_request_pad (compositor, compositorPad);
+  gst_object_unref (compositorPad);
+  gst_object_unref (compositor);
+
+  return pspec->value_type;
+}
+
 static void
 _weak_notify_cb (GstFramePositioner * pos, GObject * old)
 {
@@ -426,6 +451,11 @@ gst_frame_positioner_dispose (GObject * object)
 static void
 gst_frame_positioner_class_init (GstFramePositionerClass * klass)
 {
+  int default_operator_value;
+  GType operator_gtype =
+      gst_compositor_operator_get_type_and_default_value
+      (&default_operator_value);
+
   GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
   GstBaseTransformClass *base_transform_class =
       GST_BASE_TRANSFORM_CLASS (klass);
@@ -501,6 +531,17 @@ gst_frame_positioner_class_init (GstFramePositionerClass * klass)
       g_param_spec_int ("height", "height", "height of the source", 0,
       MAX_PIXELS, 0, G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE);
 
+  /**
+   * gesframepositioner:operator:
+   *
+   * The blending operator for the source.
+   */
+  properties[PROP_OPERATOR] =
+      g_param_spec_enum ("operator", "Operator",
+      "Blending operator to use for blending this pad over the previous ones",
+      operator_gtype, default_operator_value,
+      (G_PARAM_READWRITE | GST_PARAM_CONTROLLABLE | G_PARAM_STATIC_STRINGS));
+
   g_object_class_install_properties (gobject_class, PROP_LAST, properties);
 
   gst_element_class_set_static_metadata (GST_ELEMENT_CLASS (klass),
@@ -518,6 +559,7 @@ gst_frame_positioner_init (GstFramePositioner * framepositioner)
   framepositioner->zorder = 0;
   framepositioner->width = 0;
   framepositioner->height = 0;
+  framepositioner->operator = 1;
   framepositioner->fps_n = -1;
   framepositioner->fps_d = -1;
   framepositioner->track_width = 0;
@@ -570,6 +612,11 @@ gst_frame_positioner_set_property (GObject * object, guint property_id,
       gst_frame_positioner_update_properties (framepositioner, track_mixing,
           0, 0);
       break;
+    case PROP_OPERATOR:
+      framepositioner->operator = g_value_get_enum (value);
+      gst_frame_positioner_update_properties (framepositioner, track_mixing,
+          0, 0);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
       break;
@@ -615,6 +662,9 @@ gst_frame_positioner_get_property (GObject * object, guint property_id,
         g_value_set_int (value, real_height);
       }
       break;
+    case PROP_OPERATOR:
+      g_value_set_enum (value, pos->operator);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
       break;
@@ -655,13 +705,17 @@ static gboolean
 gst_frame_positioner_meta_init (GstMeta * meta, gpointer params,
     GstBuffer * buffer)
 {
+  int default_operator_value;
   GstFramePositionerMeta *smeta;
 
   smeta = (GstFramePositionerMeta *) meta;
 
+  gst_compositor_operator_get_type_and_default_value (&default_operator_value);
+
   smeta->alpha = 0.0;
   smeta->posx = smeta->posy = smeta->height = smeta->width = 0;
   smeta->zorder = 0;
+  smeta->operator = default_operator_value;
 
   return TRUE;
 }
@@ -685,6 +739,7 @@ gst_frame_positioner_meta_transform (GstBuffer * dest, GstMeta * meta,
     dmeta->width = smeta->width;
     dmeta->height = smeta->height;
     dmeta->zorder = smeta->zorder;
+    dmeta->operator = smeta->operator;
   }
 
   return TRUE;
@@ -712,6 +767,7 @@ gst_frame_positioner_transform_ip (GstBaseTransform * trans, GstBuffer * buf)
   meta->width = round (framepositioner->width);
   meta->height = round (framepositioner->height);
   meta->zorder = framepositioner->zorder;
+  meta->operator = framepositioner->operator;
   GST_OBJECT_UNLOCK (framepositioner);
 
   return GST_FLOW_OK;

ges/gstframepositioner.h

@@ -52,6 +52,7 @@ struct _GstFramePositioner
   guint zorder;
   gdouble width;
   gdouble height;
+  gint operator;
   gint natural_width;
   gint natural_height;
   gint track_width;
@@ -81,6 +82,7 @@ struct _GstFramePositionerMeta {
   gint height;
   gint width;
   guint zorder;
+  gint operator;
 };
 
 G_GNUC_INTERNAL void ges_frame_positioner_set_source_and_filter (GstFramePositioner *pos,