timeline-tree: simplify and fix editing

Editing has been simplified by breaking down each edit into a
combination of three basic single-element edits: MOVE, TRIM_START, and
TRIM_END.

Each edit follows these steps:
+ Determine which elements are to be edited and under which basic mode
+ Determine which track elements will move as a result
+ Snap the edit position to one of the edges of the main edited element,
  (or the edge of one of its descendants, in the case of MOVE), avoiding
  moving elements.
  NOTE: in particular, we can *not* snap to the edge of a neighbouring
  element in a roll edit. This was previously possible, even though the
  neighbour was moving!
+ Determine the edit positions for clips (or track elements with no
  parent) using the snapped value. In addition, we replace any edits of
  a group with an edit of its descendant clips. If any value would be
  out of bounds (e.g. negative start) we do not edit.
  NOTE: this is now done *after* checking the snapping. This allows the
  edit to succeed if snapping would cause it to go from being invalid to
  valid!
+ Determine whether the collection of edits would result in a valid
  timeline-configuration which does not break the rules for sources
  overlapping.
+ If all this succeeds, we emit snapping-started on the timeline.
+ We then perform all the edits. At this point they should all succeed.

The simplification/unification should make it easier to make other
changes.

Fixes https://gitlab.freedesktop.org/gstreamer/gst-editing-services/-/issues/97
Fixes https://gitlab.freedesktop.org/gstreamer/gst-editing-services/-/issues/98

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-editing-services/-/merge_requests/169>

1 files changed, 19 insertions, 0 deletions

diff --git a/ges/ges-enums.c b/ges/ges-enums.c
index fe261cac..8a684161 100644
--- a/ges/ges-enums.c
+++ b/ges/ges-enums.c
@@ -144,6 +144,25 @@ register_ges_edit_mode (GType * id)
   *id = g_enum_register_static ("GESEditMode", edit_mode);
 }
 
+const gchar *
+ges_edit_mode_name (GESEditMode mode)
+{
+  switch (mode) {
+    case GES_EDIT_MODE_NORMAL:
+      return "normal";
+    case GES_EDIT_MODE_RIPPLE:
+      return "ripple";
+    case GES_EDIT_MODE_ROLL:
+      return "roll";
+    case GES_EDIT_MODE_TRIM:
+      return "trim";
+    case GES_EDIT_MODE_SLIDE:
+      return "slide";
+    default:
+      return "unknown";
+  }
+}
+
 GType
 ges_edit_mode_get_type (void)
 {