From b6f28a6732f58edba952063c01e652a05f2e725a Mon Sep 17 00:00:00 2001
From: "Anthony J. Thibault" <tony@highfidelity.io>
Date: Wed, 4 Sep 2019 17:06:21 -0700
Subject: [PATCH] Switch additive animation deltas from a pre multiply to a
 post multiply.

---
 libraries/animation/src/AnimBlendLinear.cpp |  8 +++-----
 libraries/animation/src/AnimClip.cpp        | 18 +++++++-----------
 libraries/animation/src/AnimUtil.cpp        |  3 +--
 3 files changed, 11 insertions(+), 18 deletions(-)

diff --git a/libraries/animation/src/AnimBlendLinear.cpp b/libraries/animation/src/AnimBlendLinear.cpp
index c066dc92eb..d861f07847 100644
--- a/libraries/animation/src/AnimBlendLinear.cpp
+++ b/libraries/animation/src/AnimBlendLinear.cpp
@@ -110,11 +110,9 @@ void AnimBlendLinear::evaluateAndBlendChildren(const AnimVariantMap& animVars, c
                     // copy translation and scale from nextPoses
                     AnimPose pose = nextPoses[i];
 
-                    int parentIndex = _skeleton->getParentIndex((int)i);
-                    if (parentIndex >= 0) {
-                        // but transform nextPoses rot into absPrev parent frame.
-                        pose.rot() = glm::inverse(absPrev[parentIndex].rot()) * pose.rot() * absPrev[parentIndex].rot();
-                    }
+                    // convert from a rotation that happens in the absolute space of the joint
+                    // into a rotation that happens in the relative space of the joint.
+                    pose.rot() = glm::inverse(absPrev[i].rot()) * pose.rot() * absPrev[i].rot();
 
                     relOffsetPoses.push_back(pose);
                 }
diff --git a/libraries/animation/src/AnimClip.cpp b/libraries/animation/src/AnimClip.cpp
index 1a33cc33d2..3476adc80c 100644
--- a/libraries/animation/src/AnimClip.cpp
+++ b/libraries/animation/src/AnimClip.cpp
@@ -56,12 +56,12 @@ static void bakeRelativeDeltaAnim(std::vector<AnimPoseVec>& anim, const AnimPose
         // for each joint in animPoses
         for (size_t i = 0; i < animPoses.size(); ++i) {
             // convert this relative AnimPose into a delta animation.
-            animPoses[i] = animPoses[i] * invBasePoses[i];
+            animPoses[i] = invBasePoses[i] * animPoses[i];
         }
     }
 }
 
-void bakeAbsoluteDeltaAnim(std::vector<AnimPoseVec>& anim, const AnimPoseVec& basePoses, AnimSkeleton::ConstPointer skeleton, const QString& url, int baseFrame) {
+void bakeAbsoluteDeltaAnim(std::vector<AnimPoseVec>& anim, const AnimPoseVec& basePoses, AnimSkeleton::ConstPointer skeleton) {
 
     // invert all the basePoses
     AnimPoseVec invBasePoses = basePoses;
@@ -73,7 +73,6 @@ void bakeAbsoluteDeltaAnim(std::vector<AnimPoseVec>& anim, const AnimPoseVec& ba
     skeleton->convertRelativePosesToAbsolute(absBasePoses);
 
     // for each frame of the animation
-    int frame = 0;
     for (auto&& animPoses : anim) {
         ASSERT(animPoses.size() == basePoses.size());
 
@@ -81,15 +80,12 @@ void bakeAbsoluteDeltaAnim(std::vector<AnimPoseVec>& anim, const AnimPoseVec& ba
         for (size_t i = 0; i < animPoses.size(); ++i) {
 
             // scale and translation are relative frame
-            animPoses[i] = animPoses[i] * invBasePoses[i];
+            animPoses[i] = invBasePoses[i] * animPoses[i];
 
-            // but transform the rotation delta into the absolute frame.
-            int parentIndex = skeleton->getParentIndex((int)i);
-            if (parentIndex >= 0) {
-                animPoses[i].rot() = absBasePoses[parentIndex].rot() * animPoses[i].rot() * glm::inverse(absBasePoses[parentIndex].rot());
-            }
+            // convert from a rotation that happens in the relative space of the joint
+            // into a rotation that happens in the absolute space of the joint.
+            animPoses[i].rot() = absBasePoses[i].rot() * animPoses[i].rot() * glm::inverse(absBasePoses[i].rot());
         }
-        frame++;
     }
 }
 
@@ -297,7 +293,7 @@ const AnimPoseVec& AnimClip::evaluate(const AnimVariantMap& animVars, const Anim
             auto baseAnim = copyAndRetargetFromNetworkAnim(_baseNetworkAnim, _skeleton);
 
             if (_blendType == AnimBlendType_AddAbsolute) {
-                bakeAbsoluteDeltaAnim(_anim, baseAnim[(int)_baseFrame], _skeleton, _url, _baseFrame);
+                bakeAbsoluteDeltaAnim(_anim, baseAnim[(int)_baseFrame], _skeleton);
             } else {
                 // AnimBlendType_AddRelative
                 bakeRelativeDeltaAnim(_anim, baseAnim[(int)_baseFrame]);
diff --git a/libraries/animation/src/AnimUtil.cpp b/libraries/animation/src/AnimUtil.cpp
index dff7bb194c..8830cb78b1 100644
--- a/libraries/animation/src/AnimUtil.cpp
+++ b/libraries/animation/src/AnimUtil.cpp
@@ -68,8 +68,7 @@ void blendAdd(size_t numPoses, const AnimPose* a, const AnimPose* b, float alpha
             delta = -delta;
         }
         delta = glm::lerp(identity, delta, alpha);
-        result[i].rot() = glm::normalize(delta * aPose.rot());
-
+        result[i].rot() = glm::normalize(aPose.rot() * delta);
         result[i].trans() = aPose.trans() + (alpha * bPose.trans());
     }
 }