Fix T36496: unwanted behavior with NLA strip blend mode Replace.

If you have two overlapping NLA strips it automatically blends between them.
However it was also blending between the first strip and the rest pose
(e.g. 0,0,0 for locations and 1,1,1 for scale).

This is ok if the blend mode is Add or Multiply since then you are adding onto
the rest pose, but for Replace you want to be able to mix between two poses
and not take the rest pose into account at all.

What this does is that to not do any blending for the first strip if it has
blend mode Replace. If someone wants the old behavior (from bugfix commit
27d792fa9ca1) they can still make an action with the rest pose and use that
as the first strip.

1 files changed, 16 insertions, 5 deletions

diff --git a/source/blender/blenkernel/intern/anim_sys.c b/source/blender/blenkernel/intern/anim_sys.c
index 4e66a6665ae..3088f2ccf9b 100644
--- a/source/blender/blenkernel/intern/anim_sys.c
+++ b/source/blender/blenkernel/intern/anim_sys.c
@@ -1798,7 +1798,7 @@ static void nlaevalchan_value_init(NlaEvalChannel *nec)
 }
 
 /* verify that an appropriate NlaEvalChannel for this F-Curve exists */
-static NlaEvalChannel *nlaevalchan_verify(PointerRNA *ptr, ListBase *channels, NlaEvalStrip *nes, FCurve *fcu)
+static NlaEvalChannel *nlaevalchan_verify(PointerRNA *ptr, ListBase *channels, NlaEvalStrip *nes, FCurve *fcu, bool *newChan)
 {
 	NlaEvalChannel *nec;
 	NlaStrip *strip = nes->strip;
@@ -1841,19 +1841,29 @@ static NlaEvalChannel *nlaevalchan_verify(PointerRNA *ptr, ListBase *channels, N
 		
 		/* initialise value using default value of property [#35856] */
 		nlaevalchan_value_init(nec);
+		*newChan = true;
 	}
+	else
+		*newChan = false;
 	
 	/* we can now return */
 	return nec;
 }
 
 /* accumulate (i.e. blend) the given value on to the channel it affects */
-static void nlaevalchan_accumulate(NlaEvalChannel *nec, NlaEvalStrip *nes, float value)
+static void nlaevalchan_accumulate(NlaEvalChannel *nec, NlaEvalStrip *nes, float value, bool newChan)
 {
 	NlaStrip *strip = nes->strip;
 	short blendmode = strip->blendmode;
 	float inf = strip->influence;
 	
+	/* for replace blend mode, and if this is the first strip,
+	 * just replace the value regardless of the influence */
+	if (newChan && blendmode == NLASTRIP_MODE_REPLACE) {
+		nec->value = value;
+		return;
+	}
+
 	/* if this is being performed as part of transition evaluation, incorporate
 	 * an additional weighting factor for the influence
 	 */
@@ -1915,7 +1925,7 @@ static void nlaevalchan_buffers_accumulate(ListBase *channels, ListBase *tmp_buf
 		 * otherwise, add the current channel to the buffer for efficiency
 		 */
 		if (necd)
-			nlaevalchan_accumulate(necd, nes, nec->value);
+			nlaevalchan_accumulate(necd, nes, 0, nec->value);
 		else {
 			BLI_remlink(tmp_buffer, nec);
 			BLI_addtail(channels, nec);
@@ -2014,6 +2024,7 @@ static void nlastrip_evaluate_actionclip(PointerRNA *ptr, ListBase *channels, Li
 	for (fcu = strip->act->curves.first; fcu; fcu = fcu->next) {
 		NlaEvalChannel *nec;
 		float value = 0.0f;
+		bool newChan;
 		
 		/* check if this curve should be skipped */
 		if (fcu->flag & (FCURVE_MUTED | FCURVE_DISABLED))
@@ -2035,9 +2046,9 @@ static void nlastrip_evaluate_actionclip(PointerRNA *ptr, ListBase *channels, Li
 		/* get an NLA evaluation channel to work with, and accumulate the evaluated value with the value(s)
 		 * stored in this channel if it has been used already
 		 */
-		nec = nlaevalchan_verify(ptr, channels, nes, fcu);
+		nec = nlaevalchan_verify(ptr, channels, nes, fcu, &newChan);
 		if (nec)
-			nlaevalchan_accumulate(nec, nes, value);
+			nlaevalchan_accumulate(nec, nes, value, newChan);
 	}
 
 	/* free temporary storage */