Fix VSE strip channel skip overlapping strips

D1096 by @mangostaniko (with some edits)

3 files changed, 26 insertions, 12 deletions

diff --git a/source/blender/blenkernel/BKE_sequencer.h b/source/blender/blenkernel/BKE_sequencer.h
index 7a47d7cecc1..c936ce5284d 100644
--- a/source/blender/blenkernel/BKE_sequencer.h
+++ b/source/blender/blenkernel/BKE_sequencer.h
@@ -314,7 +314,11 @@ struct Sequence *BKE_sequence_metastrip(ListBase *seqbase /* = ed->seqbase */, s
 
 void BKE_sequencer_offset_animdata(struct Scene *scene, struct Sequence *seq, int ofs);
 void BKE_sequencer_dupe_animdata(struct Scene *scene, const char *name_src, const char *name_dst);
-bool BKE_sequence_base_shuffle(struct ListBase *seqbasep, struct Sequence *test, struct Scene *evil_scene);
+bool BKE_sequence_base_shuffle_ex(
+        struct ListBase *seqbasep, struct Sequence *test, struct Scene *evil_scene,
+        int channel_delta);
+bool BKE_sequence_base_shuffle(
+        struct ListBase *seqbasep, struct Sequence *test, struct Scene *evil_scene);
 bool BKE_sequence_base_shuffle_time(ListBase *seqbasep, struct Scene *evil_scene);
 bool BKE_sequence_base_isolated_sel_check(struct ListBase *seqbase);
 void BKE_sequencer_free_imbuf(struct Scene *scene, struct ListBase *seqbasep, bool for_render);
diff --git a/source/blender/blenkernel/intern/sequencer.c b/source/blender/blenkernel/intern/sequencer.c
index 83287fe7725..cb23b1eb88e 100644
--- a/source/blender/blenkernel/intern/sequencer.c
+++ b/source/blender/blenkernel/intern/sequencer.c
@@ -3764,21 +3764,23 @@ Sequence *BKE_sequencer_foreground_frame_get(Scene *scene, int frame)
 }
 
 /* return 0 if there werent enough space */
-bool BKE_sequence_base_shuffle(ListBase *seqbasep, Sequence *test, Scene *evil_scene)
+bool BKE_sequence_base_shuffle_ex(ListBase *seqbasep, Sequence *test, Scene *evil_scene, int channel_delta)
 {
-	int orig_machine = test->machine;
-	test->machine++;
+	const int orig_machine = test->machine;
+	BLI_assert(ELEM(channel_delta, -1, 1));
+
+	test->machine += channel_delta;
 	BKE_sequence_calc(evil_scene, test);
-	while (BKE_sequence_test_overlap(seqbasep, test) ) {
-		if (test->machine >= MAXSEQ) {
+	while (BKE_sequence_test_overlap(seqbasep, test)) {
+		if ((channel_delta > 0) ? (test->machine >= MAXSEQ) : (test->machine <= 1)) {
 			break;
 		}
-		test->machine++;
+
+		test->machine += channel_delta;
 		BKE_sequence_calc(evil_scene, test); // XXX - I don't think this is needed since were only moving vertically, Campbell.
 	}
 
-	
-	if (test->machine >= MAXSEQ) {
+	if ((test->machine < 1) || (test->machine > MAXSEQ)) {
 		/* Blender 2.4x would remove the strip.
 		 * nicer to move it to the end */
 
@@ -3802,6 +3804,11 @@ bool BKE_sequence_base_shuffle(ListBase *seqbasep, Sequence *test, Scene *evil_s
 	}
 }
 
+bool BKE_sequence_base_shuffle(ListBase *seqbasep, Sequence *test, Scene *evil_scene)
+{
+	return BKE_sequence_base_shuffle_ex(seqbasep, test, evil_scene, 1);
+}
+
 static int shuffle_seq_time_offset_test(ListBase *seqbasep, char dir)
 {
 	int offset = 0;
diff --git a/source/blender/makesrna/intern/rna_sequencer.c b/source/blender/makesrna/intern/rna_sequencer.c
index 927e77960d7..8ad7d313c1e 100644
--- a/source/blender/makesrna/intern/rna_sequencer.c
+++ b/source/blender/makesrna/intern/rna_sequencer.c
@@ -290,11 +290,14 @@ static void rna_Sequence_channel_set(PointerRNA *ptr, int value)
 	Scene *scene = (Scene *)ptr->id.data;
 	Editing *ed = BKE_sequencer_editing_get(scene, false);
 	ListBase *seqbase = BKE_sequence_seqbase(&ed->seqbase, seq);
-
-	seq->machine = value;
 	
+	/* check channel increment or decrement */
+	const int channel_delta = (value >= seq->machine) ? 1 : -1;
+	seq->machine = value;
+
 	if (BKE_sequence_test_overlap(seqbase, seq)) {
-		BKE_sequence_base_shuffle(seqbase, seq, scene);  /* XXX - BROKEN!, uses context seqbasep */
+		/* XXX - BROKEN!, uses context seqbasep */
+		BKE_sequence_base_shuffle_ex(seqbase, seq, scene, channel_delta);
 	}
 	BKE_sequencer_sort(scene);
 }