Interpolate euler rotations for quaternion animations

FBX uses euler rotation but assimp library's base type is
quaternion. When assimp convert FBX some animation information
can be lost.
This patch interpolates euler-angle rotations and insert
additional keyframes for the FBX format.

code/AssetLib/FBX/FBXConverter.cpp

@@ -3127,7 +3127,12 @@ aiNodeAnim* FBXConverter::GenerateSimpleNodeAnim(const std::string& name,
         if (chain[i] == iterEnd)
             continue;
 
-        keyframeLists[i] = GetKeyframeList((*chain[i]).second, start, stop);
+        if (i == TransformationComp_Rotation || i == TransformationComp_PreRotation
+                || i == TransformationComp_PostRotation || i == TransformationComp_GeometricRotation) {
+            keyframeLists[i] = GetRotationKeyframeList((*chain[i]).second, start, stop);
+        } else {
+            keyframeLists[i] = GetKeyframeList((*chain[i]).second, start, stop);
+        }
 
         for (KeyFrameListList::const_iterator it = keyframeLists[i].begin(); it != keyframeLists[i].end(); ++it) {
             const KeyTimeList& times = *std::get<0>(*it);
@@ -3274,6 +3279,79 @@ FBXConverter::KeyFrameListList FBXConverter::GetKeyframeList(const std::vector<c
     return inputs; // pray for NRVO :-)
 }
 
+FBXConverter::KeyFrameListList FBXConverter::GetRotationKeyframeList(const std::vector<const AnimationCurveNode *> &nodes,
+                                                                     int64_t start, int64_t stop) {
+    KeyFrameListList inputs;
+    inputs.reserve(nodes.size() * 3);
+
+    //give some breathing room for rounding errors
+    const int64_t adj_start = start - 10000;
+    const int64_t adj_stop = stop + 10000;
+
+    for (const AnimationCurveNode *node : nodes) {
+        ai_assert(node);
+
+        const AnimationCurveMap &curves = node->Curves();
+        for (const AnimationCurveMap::value_type &kv : curves) {
+
+            unsigned int mapto;
+            if (kv.first == "d|X") {
+                mapto = 0;
+            } else if (kv.first == "d|Y") {
+                mapto = 1;
+            } else if (kv.first == "d|Z") {
+                mapto = 2;
+            } else {
+                FBXImporter::LogWarn("ignoring scale animation curve, did not recognize target component");
+                continue;
+            }
+
+            const AnimationCurve *const curve = kv.second;
+            ai_assert(curve->GetKeys().size() == curve->GetValues().size());
+            ai_assert(curve->GetKeys().size());
+
+            //get values within the start/stop time window
+            std::shared_ptr<KeyTimeList> Keys(new KeyTimeList());
+            std::shared_ptr<KeyValueList> Values(new KeyValueList());
+            const size_t count = curve->GetKeys().size();
+
+            int64_t tp = curve->GetKeys().at(0);
+            float vp = curve->GetValues().at(0);
+            Keys->push_back(tp);
+            Values->push_back(vp);
+            if (count > 1) {
+                int64_t tc = curve->GetKeys().at(1);
+                float vc = curve->GetValues().at(1);
+                for (size_t n = 1; n < count; n++) {
+                    while (std::abs(vc - vp) >= 180.0f) {
+                        float step = std::floor(float(tc - tp) / (vc - vp) * 179.0f);
+                        int64_t tnew = tp + int64_t(step);
+                        float vnew = vp + (vc - vp) * step / float(tc - tp);
+                        if (tnew >= adj_start && tnew <= adj_stop) {
+                            Keys->push_back(tnew);
+                            Values->push_back(vnew);
+                        }
+                        tp = tnew;
+                        vp = vnew;
+                    }
+                    if (tc >= adj_start && tc <= adj_stop) {
+                        Keys->push_back(tc);
+                        Values->push_back(vc);
+                    }
+                    if (n + 1 < count) {
+                        tp = tc;
+                        vp = vc;
+                        tc = curve->GetKeys().at(n + 1);
+                        vc = curve->GetValues().at(n + 1);
+                    }
+                }
+            }
+            inputs.push_back(std::make_tuple(Keys, Values, mapto));
+        }
+    }
+    return inputs;
+}
+
 KeyTimeList FBXConverter::GetKeyTimeList(const KeyFrameListList &inputs) {
     ai_assert(!inputs.empty());
 
@@ -3464,7 +3542,7 @@ void FBXConverter::ConvertRotationKeys(aiNodeAnim *na, const std::vector<const A
     ai_assert(nodes.size());
 
     // XXX see notes in ConvertScaleKeys()
-    const std::vector<KeyFrameList> &inputs = GetKeyframeList(nodes, start, stop);
+    const std::vector<KeyFrameList> &inputs = GetRotationKeyframeList(nodes, start, stop);
     const KeyTimeList &keys = GetKeyTimeList(inputs);
 
     na->mNumRotationKeys = static_cast<unsigned int>(keys.size());

code/AssetLib/FBX/FBXConverter.h

@@ -361,6 +361,7 @@ private:
 
     // ------------------------------------------------------------------------------------------------
     KeyFrameListList GetKeyframeList(const std::vector<const AnimationCurveNode*>& nodes, int64_t start, int64_t stop);
+    KeyFrameListList GetRotationKeyframeList(const std::vector<const AnimationCurveNode*>& nodes, int64_t start, int64_t stop);
 
     // ------------------------------------------------------------------------------------------------
     KeyTimeList GetKeyTimeList(const KeyFrameListList& inputs);