VSE: Remove still frame offsets

To clarify term still frame: This is portion of strip that displays
static image. This area can exist before or after strip movie content.

Still frames were implemented as strip property, but this was never
displayed in panel. Only way to set still frames was to drag strip
handle with mouse or using python API. This would set either
`seq->*still` or `seq->*ofs` where * stands for `start` or `end`.

When strip had offset, it can't have still frames and vice versa, but
this had to be enforced in RNA functions and everywhere in code where
these fields are set directly. Strip can not have negative offset or
negative number of still frames.

This is not very practical approach and still frames can be simply
implemented as applying negative offset. Merging these offsets would
simplify offset calculations for example in D14962 and could make it
easier to also deprecate usage `seq->*disp` and necessity to call
update functions to recalculate strip boundaries.

For users only functional change is ability to set negative strip offset
using property in side panel.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D14976

1 files changed, 17 insertions, 0 deletions

diff --git a/source/blender/blenloader/intern/versioning_300.c b/source/blender/blenloader/intern/versioning_300.c
index de47fe49946..74621a477cd 100644
--- a/source/blender/blenloader/intern/versioning_300.c
+++ b/source/blender/blenloader/intern/versioning_300.c
@@ -1217,6 +1217,15 @@ static bool version_fix_seq_meta_range(Sequence *seq, void *user_data)
   return true;
 }
 
+static bool version_merge_still_offsets(Sequence *seq, void *UNUSED(user_data))
+{
+  seq->startofs -= seq->startstill;
+  seq->endofs -= seq->endstill;
+  seq->startstill = 0;
+  seq->endstill = 0;
+  return true;
+}
+
 /* Those `version_liboverride_rnacollections_*` functions mimic the old, pre-3.0 code to find
  * anchor and source items in the given list of modifiers, constraints etc., using only the
  * `subitem_local` data of the override property operation.
@@ -3045,5 +3054,13 @@ void blo_do_versions_300(FileData *fd, Library *UNUSED(lib), Main *bmain)
         }
       }
     }
+
+    /* Merge still offsets into start/end offsets. */
+    LISTBASE_FOREACH (Scene *, scene, &bmain->scenes) {
+      Editing *ed = SEQ_editing_get(scene);
+      if (ed != NULL) {
+        SEQ_for_each_callback(&ed->seqbase, version_merge_still_offsets, NULL);
+      }
+    }
   }
 }