[cpp] Port of commit 8290353. Fix for hold previous on 3+ animations causing dipping. See #1738.

spine-cpp/spine-cpp/src/spine/AnimationState.cpp

@@ -290,8 +290,9 @@ void EventQueue::drain() {
 
 const int Subsequent = 0;
 const int First = 1;
-const int Hold = 2;
-const int HoldMix = 3;
+const int HoldSubsequent = 2;
+const int HoldFirst = 3;
+const int HoldMix = 4;
 
 const int Setup = 1;
 const int Current = 2;
@@ -836,7 +837,11 @@ float AnimationState::applyMixingFrom(TrackEntry *to, Skeleton &skeleton, MixBle
 					timelineBlend = MixBlend_Setup;
 					alpha = alphaMix;
 					break;
-				case Hold:
+			    case HoldSubsequent:
+			        timelineBlend = blend;
+			        alpha = alphaHold;
+			        break;
+				case HoldFirst:
 					timelineBlend = MixBlend_Setup;
 					alpha = alphaHold;
 					break;
@@ -1007,8 +1012,12 @@ void AnimationState::computeHold(TrackEntry *entry) {
 	if (to != NULL && to->_holdPrevious) {
 		for (size_t i = 0; i < timelinesCount; i++) {
 			int id = timelines[i]->getPropertyId();
-			if (!_propertyIDs.containsKey(id)) _propertyIDs.put(id, true);
-			timelineMode[i] = Hold;
+			if (!_propertyIDs.containsKey(id)) {
+			    _propertyIDs.put(id, true);
+                timelineMode[i] = HoldFirst;
+			} else {
+                timelineMode[i] = HoldSubsequent;
+            }
 		}
 		return;
 	}
@@ -1039,7 +1048,7 @@ void AnimationState::computeHold(TrackEntry *entry) {
 					}
 					break;
 				}
-				timelineMode[i] = Hold;
+				timelineMode[i] = HoldFirst;
 			}
 		}
 	}