From 50919413fe7b3fd3e3cbf189e42a48936984b9ce Mon Sep 17 00:00:00 2001
From: Wayde Moss <GuiltyGhost>
Date: Thu, 20 Aug 2020 16:22:44 +0200
Subject: NLA: Fix strip Sync Length moving animation data

Change the way Sync Length works so that it keeps keyframes at the same
key as before the sync. Now when the user exits tweak mode, the overall
NLA result is unchanged.

Reviewed By: sybren

Differential Revision: https://developer.blender.org/D7602
---
 source/blender/blenkernel/intern/nla.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

(limited to 'source/blender/blenkernel/intern/nla.c')

diff --git a/source/blender/blenkernel/intern/nla.c b/source/blender/blenkernel/intern/nla.c
index 1ba82b352d1..e5527ed987a 100644
--- a/source/blender/blenkernel/intern/nla.c
+++ b/source/blender/blenkernel/intern/nla.c
@@ -1361,6 +1361,25 @@ static void nlastrip_fix_resize_overlaps(NlaStrip *strip)
   }
 }
 
+/** Recalculate the start and end frames for the strip to match the bounds of its action such that
+ * the overall NLA animation result is unchanged. */
+void BKE_nlastrip_recalculate_bounds_sync_action(NlaStrip *strip)
+{
+  float prev_actstart;
+
+  if (strip == NULL || strip->type != NLASTRIP_TYPE_CLIP) {
+    return;
+  }
+
+  prev_actstart = strip->actstart;
+
+  calc_action_range(strip->act, &strip->actstart, &strip->actend, 0);
+
+  /* Set start such that key's do not visually move, to preserve the overall animation result. */
+  strip->start += (strip->actstart - prev_actstart) * strip->scale;
+
+  BKE_nlastrip_recalculate_bounds(strip);
+}
 /* Recalculate the start and end frames for the current strip, after changing
  * the extents of the action or the mapping (repeats or scale factor) info
  */
@@ -2133,11 +2152,7 @@ void BKE_nla_tweakmode_exit(AnimData *adt)
 
     /* must be action-clip only (transitions don't have scale) */
     if ((strip->type == NLASTRIP_TYPE_CLIP) && (strip->act)) {
-      /* recalculate the length of the action */
-      calc_action_range(strip->act, &strip->actstart, &strip->actend, 0);
-
-      /* adjust the strip extents in response to this */
-      BKE_nlastrip_recalculate_bounds(strip);
+      BKE_nlastrip_recalculate_bounds_sync_action(strip);
     }
   }
 
@@ -2151,11 +2166,7 @@ void BKE_nla_tweakmode_exit(AnimData *adt)
       /* sync strip extents if this strip uses the same action */
       if ((adt->actstrip) && (adt->actstrip->act == strip->act) &&
           (strip->flag & NLASTRIP_FLAG_SYNC_LENGTH)) {
-        /* recalculate the length of the action */
-        calc_action_range(strip->act, &strip->actstart, &strip->actend, 0);
-
-        /* adjust the strip extents in response to this */
-        BKE_nlastrip_recalculate_bounds(strip);
+        BKE_nlastrip_recalculate_bounds_sync_action(strip);
       }
 
       /* clear tweakuser flag */
-- 
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