[385/906] rewrite the way a gstgldisplay is transmited to the gl elements

Before, a gstgldisplay was instancied by the gl src in terms of gl chain.
And then the next element got it through the first gstglbuffer.
Now, this is done though queries.
All glelements get their ref on a gstgldisplay in READY state.
This rewrite is mainly a first step to be able to share OpenGL context hold
by the gstgldisplay using more complex glelements.
For example, with a glvideomixer. The associated gstgldisplay of each gl chain
of the sink pads will share their OpenGL context.

gst-libs/gst/gl/gstglfilter.c

@@ -55,6 +55,8 @@ static void gst_gl_filter_set_property (GObject * object, guint prop_id,
 static void gst_gl_filter_get_property (GObject * object, guint prop_id,
     GValue * value, GParamSpec * pspec);
 
+static gboolean gst_gl_filter_src_query (GstPad *pad, GstQuery * query);
+
 static GstCaps *gst_gl_filter_transform_caps (GstBaseTransform * bt,
     GstPadDirection direction, GstCaps * caps);
 static void gst_gl_filter_reset (GstGLFilter * filter);
@@ -118,10 +120,10 @@ gst_gl_filter_class_init (GstGLFilterClass * klass)
 static void
 gst_gl_filter_init (GstGLFilter * filter, GstGLFilterClass * klass)
 {
-  //gst_element_create_all_pads (GST_ELEMENT (filter));
+  GstBaseTransform *base_trans = GST_BASE_TRANSFORM (filter);
-
+  
-  filter->sinkpad = gst_element_get_static_pad (GST_ELEMENT (filter), "sink");
+  gst_pad_set_query_function (base_trans->srcpad,
-  filter->srcpad = gst_element_get_static_pad (GST_ELEMENT (filter), "src");
+      GST_DEBUG_FUNCPTR (gst_gl_filter_src_query));
 
   gst_gl_filter_reset (filter);
 }
@@ -152,6 +154,36 @@ gst_gl_filter_get_property (GObject * object, guint prop_id,
   }
 }
 
+static gboolean
+gst_gl_filter_src_query (GstPad * pad, GstQuery * query)
+{
+  gboolean res = FALSE;
+  GstElement *parent = GST_ELEMENT (gst_pad_get_parent (pad));
+  GstGLFilter *filter = GST_GL_FILTER (parent);
+
+  switch (GST_QUERY_TYPE (query)) {
+    case GST_QUERY_CUSTOM:
+    {
+      GstStructure *structure = gst_query_get_structure (query);
+      if (filter->display) {
+        /* this gl filter is a sink in terms of the gl chain */
+        gst_structure_set (structure, "gstgldisplay", G_TYPE_POINTER, filter->display, NULL);
+      } else {
+        /* at least one gl element is before in our gl chain */
+        res = g_strcmp0 (gst_element_get_name (parent), gst_structure_get_name (structure)) == 0;
+      }
+      if (!res)
+        res = gst_pad_query_default (pad, query);
+      break;
+    }
+    default:
+      res = gst_pad_query_default (pad, query);
+      break;
+  }
+
+  return res;
+}
+
 static void
 gst_gl_filter_reset (GstGLFilter * filter)
 {
@@ -181,6 +213,27 @@ gst_gl_filter_start (GstBaseTransform * bt)
 {
   GstGLFilter *filter = GST_GL_FILTER (bt);
   GstGLFilterClass *filter_class = GST_GL_FILTER_GET_CLASS (filter);
+  GstElement *parent = GST_ELEMENT (gst_element_get_parent (filter));
+  GstStructure *structure = gst_structure_new (gst_element_get_name (filter), NULL);
+  GstQuery *query = gst_query_new_application (GST_QUERY_CUSTOM, structure);
+
+  gboolean isPerformed = gst_element_query (parent, query);
+
+  if (isPerformed) {
+    const GValue *id_value = gst_structure_get_value (structure, "gstgldisplay");
+    if (G_VALUE_HOLDS_POINTER (id_value))
+      /* at least one gl element is before in our gl chain */
+      filter->display = g_object_ref (GST_GL_DISPLAY (g_value_get_pointer (id_value)));
+    else
+      /* this gl filter is a sink in terms of the gl chain */
+      filter->display = gst_gl_display_new ();
+  }
+
+  gst_query_unref (query);
+  gst_object_unref (GST_OBJECT (parent));
+
+  if (!isPerformed)
+    return FALSE;
 
   if (filter_class->onStart)
     filter_class->onStart (filter);
@@ -275,24 +328,6 @@ gst_gl_filter_prepare_output_buffer (GstBaseTransform * trans,
 
   filter = GST_GL_FILTER (trans);
 
-  if (filter->display == NULL) {
-    GstGLFilterClass *filter_class = GST_GL_FILTER_GET_CLASS (filter);
-
-    filter->display = g_object_ref (gl_inbuf->display);
-
-    //blocking call, generate a FBO
-    gst_gl_display_gen_fbo (filter->display, filter->width, filter->height,
-        &filter->fbo, &filter->depthbuffer);
-
-    if (filter_class->display_init_cb != NULL) {
-      gst_gl_display_thread_add (filter->display, gst_gl_filter_start_gl,
-          filter);
-    }
-
-    if (filter_class->onInitFBO)
-      filter_class->onInitFBO (filter);
-  }
-
   gl_outbuf = gst_gl_buffer_new (filter->display,
       filter->width, filter->height);
 
@@ -313,8 +348,23 @@ gst_gl_filter_set_caps (GstBaseTransform * bt, GstCaps * incaps,
   gboolean ret = FALSE;
   GstGLFilterClass *filter_class = GST_GL_FILTER_GET_CLASS (filter);
 
+  if (!filter->display)
+    return FALSE;
+
   ret = gst_gl_buffer_parse_caps (outcaps, &filter->width, &filter->height);
 
+  //blocking call, generate a FBO
+  gst_gl_display_gen_fbo (filter->display, filter->width, filter->height,
+      &filter->fbo, &filter->depthbuffer);
+
+  if (filter_class->display_init_cb != NULL) {
+    gst_gl_display_thread_add (filter->display, gst_gl_filter_start_gl,
+        filter);
+  }
+
+  if (filter_class->onInitFBO)
+    filter_class->onInitFBO (filter);
+
   if (filter_class->set_caps)
     filter_class->set_caps (filter, incaps, outcaps);
 

gst-libs/gst/gl/gstglfilter.h

@@ -57,9 +57,6 @@ struct _GstGLFilter
 {
   GstBaseTransform base_transform;
 
-  GstPad *srcpad;
-  GstPad *sinkpad;
-
   GstGLDisplay *display;
 
   gint width;