Fix T46678: Extending left handle of a VSE multicam effect strip with snap creates frame stills.

Also fixes cache handling for those strips, they need more radical flushing...

source/blender/blenkernel/BKE_sequencer.h

@@ -314,6 +314,7 @@ void BKE_sequence_tx_set_final_left(struct Sequence *seq, int val);
 void BKE_sequence_tx_set_final_right(struct Sequence *seq, int val);
 void BKE_sequence_tx_handle_xlimits(struct Sequence *seq, int leftflag, int rightflag);
 bool BKE_sequence_tx_test(struct Sequence *seq);
+bool BKE_sequence_tx_fullupdate_test(struct Sequence *seq);
 bool BKE_sequence_single_check(struct Sequence *seq);
 void BKE_sequence_single_fix(struct Sequence *seq);
 bool BKE_sequence_test_overlap(struct ListBase *seqbasep, struct Sequence *test);

source/blender/blenkernel/intern/sequencer.c

@@ -4252,6 +4252,17 @@ bool BKE_sequence_tx_test(Sequence *seq)
 	return !(seq->type & SEQ_TYPE_EFFECT) || (BKE_sequence_effect_get_num_inputs(seq->type) == 0);
 }
 
+/**
+ * Return \a true if given \a seq needs a complete cleanup of its cache when it is transformed.
+ *
+ * Some (effect) strip types need a complete recache of themselves when they are transformed, because
+ * they do not 'contain' anything and do not have any explicit relations to other strips.
+ */
+bool BKE_sequence_tx_fullupdate_test(Sequence *seq)
+{
+	return BKE_sequence_tx_test(seq) && ELEM(seq->type, SEQ_TYPE_ADJUSTMENT, SEQ_TYPE_MULTICAM);
+}
+
 static bool seq_overlap(Sequence *seq1, Sequence *seq2)
 {
 	return (seq1 != seq2 && seq1->machine == seq2->machine &&

source/blender/editors/space_sequencer/sequencer_edit.c

@@ -1206,6 +1206,7 @@ static int sequencer_snap_exec(bContext *C, wmOperator *op)
 					BKE_sequence_tx_set_final_right(seq, snap_frame);
 				}
 				BKE_sequence_tx_handle_xlimits(seq, seq->flag & SEQ_LEFTSEL, seq->flag & SEQ_RIGHTSEL);
+				BKE_sequence_single_fix(seq);
 			}
 			BKE_sequence_calc(scene, seq);
 		}
@@ -2516,6 +2517,7 @@ static int sequencer_meta_toggle_exec(bContext *C, wmOperator *UNUSED(op))
 #if 1
 		BKE_sequence_tx_set_final_left(ms->parseq, ms->disp_range[0]);
 		BKE_sequence_tx_set_final_right(ms->parseq, ms->disp_range[1]);
+		BKE_sequence_single_fix(seq);
 		BKE_sequence_calc(scene, ms->parseq);
 #else
 		if (BKE_sequence_test_overlap(ed->seqbasep, ms->parseq))

source/blender/editors/transform/transform_generics.c

@@ -951,7 +951,13 @@ static void recalcData_sequencer(TransInfo *t)
 		Sequence *seq = tdsq->seq;
 
 		if (seq != seq_prev) {
-			BKE_sequence_invalidate_dependent(t->scene, seq);
+			if (BKE_sequence_tx_fullupdate_test(seq)) {
+				/* A few effect strip types need a complete recache on transform. */
+				BKE_sequence_invalidate_cache(t->scene, seq);
+			}
+			else {
+				BKE_sequence_invalidate_dependent(t->scene, seq);
+			}
 		}
 
 		seq_prev = seq;