NLA: Extract nlasnapshot_blend()

Refactor
//nlastrip_evaluate_actionclip()// and //nlaeval_blend_value()// into
//nlasnapshot_blend()//, //nlastrip_evaluate_actionclip()//,
//nlasnapshot_from_action()//.

**Motivations**:
* {T83615} Requires reading all pose bone fcurves before being able to
apply pre-blend transforms. The function //nlasnapshot_from_action()//
achieves this. This effectively removed the need to specially handle
Quaternion blend queuing so that code has been removed.

* {D8296} Adds support for keyframe remapping through an upper stack of
strips. Instead of introducing a variant of the form:
//nlastrip_evaluate_actionclip_inverted_get_lower()//,
//nlastrip_evaluate_actionclip()// will later be extended to take an
`evaluation_mode` as input to avoid duplicating the recursion functions
related to //nlastrip_evaluate()//.

* //nlasnapshot_blend()// will eventually have variants of
//nlasnapshot_blend_get_inverted_lower_snapshot()// and
//nlasnapshot_blend_get_inverted_upper_snapshot()// which are all
independent of NlaStrips and NlaTracks, further simplifying the
blending implementation. Ideally, //nlastrip_evaluate()// would get
renamed to //nlasnapshot_blend_strip()// but that'll be a later patch
to avoid unnecessary patches slowing the review of more important
patches.

No User-side Functional changes

Reviewed By: sybren, #animation_rigging

Differential Revision: https://developer.blender.org/D10220

1 files changed, 7 insertions, 4 deletions

diff --git a/source/blender/blenkernel/nla_private.h b/source/blender/blenkernel/nla_private.h
index 034f3f39fd3..488bc5dc98b 100644
--- a/source/blender/blenkernel/nla_private.h
+++ b/source/blender/blenkernel/nla_private.h
@@ -106,12 +106,8 @@ typedef struct NlaEvalChannel {
 
   int index;
   bool is_array;
-  bool in_blend;
   char mix_mode;
 
-  struct NlaEvalChannel *next_blend;
-  NlaEvalChannelSnapshot *blend_snapshot;
-
   /* Associated with the RNA property's value(s), marks which elements are affected by NLA. */
   NlaValidMask domain;
 
@@ -186,6 +182,13 @@ void nladata_flush_channels(PointerRNA *ptr,
                             NlaEvalSnapshot *snapshot,
                             const bool flush_to_original);
 
+void nlasnapshot_blend(NlaEvalData *eval_data,
+                       NlaEvalSnapshot *lower_snapshot,
+                       NlaEvalSnapshot *upper_snapshot,
+                       const short upper_blendmode,
+                       const float upper_influence,
+                       NlaEvalSnapshot *r_blended_snapshot);
+
 #ifdef __cplusplus
 }
 #endif