gl: add EGLImage support

* picked from old libgstegl:
  - GstEGLImageMemory
  - GstEGLImageAllocator
  - last_buffer management from removed GstEGLImageBufferPool

* add-ons:
  - GstEGLImageMemory now old a reference on GstGLContext
    so that it can delete the EGLImage and its gltexture source
    while having the associated gl context being current.
  - add EGLImage support for GstVideoGLTextureUploadMeta which
    mainly call EGLImageTargetTexture2D
  - GstGLBufferPool now supports GstEGLImageAllocator
  - glimagesink / glfilters / etc.. now propose GstEGLImageAllocator
    to upstream

https://bugzilla.gnome.org/show_bug.cgi?id=703343

ext/gl/gstglimagesink.c

@@ -169,7 +169,9 @@ static GstStaticPadTemplate gst_glimage_sink_template =
     GST_STATIC_PAD_TEMPLATE ("sink",
     GST_PAD_SINK,
     GST_PAD_ALWAYS,
-    GST_STATIC_CAPS (GST_VIDEO_CAPS_MAKE (GST_GL_UPLOAD_FORMATS) "; "
+    GST_STATIC_CAPS (GST_VIDEO_CAPS_MAKE_WITH_FEATURES
+        (GST_CAPS_FEATURE_MEMORY_EGL_IMAGE,
+            "RGBA") "; " GST_VIDEO_CAPS_MAKE (GST_GL_UPLOAD_FORMATS) "; "
         GST_VIDEO_CAPS_MAKE_WITH_FEATURES
         (GST_CAPS_FEATURE_META_GST_VIDEO_GL_TEXTURE_UPLOAD_META,
             GST_GL_UPLOAD_FORMATS))
@@ -863,6 +865,8 @@ gst_glimage_sink_propose_allocation (GstBaseSink * bsink, GstQuery * query)
   GstStructure *gl_context;
   gchar *platform, *gl_apis;
   gpointer handle;
+  GstAllocator *allocator = NULL;
+  GstAllocationParams params;
 
   if (!_ensure_gl_setup (glimage_sink))
     return FALSE;
@@ -936,6 +940,18 @@ gst_glimage_sink_propose_allocation (GstBaseSink * bsink, GstQuery * query)
   g_free (platform);
   gst_structure_free (gl_context);
 
+  gst_allocation_params_init (&params);
+
+  allocator = gst_allocator_find (GST_GL_MEMORY_ALLOCATOR);
+  gst_query_add_allocation_param (query, allocator, &params);
+  gst_object_unref (allocator);
+
+#if GST_GL_HAVE_PLATFORM_EGL
+  allocator = gst_allocator_find (GST_EGL_IMAGE_MEMORY_TYPE);
+  gst_query_add_allocation_param (query, allocator, &params);
+  gst_object_unref (allocator);
+#endif
+
   return TRUE;
 
   /* ERRORS */

gst-libs/gst/gl/egl/Makefile.am

@@ -4,16 +4,16 @@ noinst_LTLIBRARIES = libgstgl-egl.la
 
 libgstgl_egl_la_SOURCES = \
 	gstgldisplay_egl.c \
-	gstglcontext_egl.c
+	gstglcontext_egl.c \
+	gsteglimagememory.c
 
 noinst_HEADERS = \
 	gstglcontext_egl.h
 
 libgstgl_eglincludedir = $(includedir)/gstreamer-@GST_API_VERSION@/gst/gl/egl
 libgstgl_eglinclude_HEADERS = \
-	gstgldisplay_egl.h
-
-libgstgl_egl_la_LIBADD = $(top_builddir)/gst-libs/gst/egl/libgstegl-$(GST_API_VERSION).la
+	gstgldisplay_egl.h \
+	gsteglimagememory.h
 
 libgstgl_egl_la_CFLAGS = \
 	-I$(top_srcdir)/gst-libs \