add manual bone transform animation

lib/animations/animations.dart

@@ -0,0 +1,69 @@
+class Vec3 {
+  final double x;
+  final double y;
+  final double z;
+
+  Vec3({this.x = 0, this.y = 0, this.z = 0});
+}
+
+class Quaternion {
+  double x = 0;
+  double y = 0;
+  double z = 0;
+  double w = 1;
+
+  Quaternion({this.x = 0, this.y = 0, this.z = 0, this.w = 1.0});
+}
+
+class BoneTransform {
+  final List<Vec3> translations;
+  final List<Quaternion> quaternions;
+
+  ///
+  /// The length of [translations] and [quaternions] must be the same;
+  /// each entry represents the Vec3/Quaternion for the given frame.
+  ///
+  BoneTransform(this.translations, this.quaternions) {
+    if (translations.length != quaternions.length) {
+      throw Exception("Length of translation/quaternion frames must match");
+    }
+    // for (int i = 0; i < quaternions.length; i++) {
+    //   _frameData.add(translations[i].x);
+    //   _frameData.add(translations[i].y);
+    //   _frameData.add(translations[i].z);
+    //   _frameData.add(quaternions[i].x);
+    //   _frameData.add(quaternions[i].y);
+    //   _frameData.add(quaternions[i].z);
+    //   _frameData.add(quaternions[i].w);
+    // }
+  }
+
+  Iterable<double> getFrameData(int frame) sync* {
+    yield translations[frame].x;
+    yield translations[frame].y;
+    yield translations[frame].z;
+    yield quaternions[frame].x;
+    yield quaternions[frame].y;
+    yield quaternions[frame].z;
+    yield quaternions[frame].w;
+  }
+}
+
+class BoneAnimation {
+  final List<BoneTransform> boneTransforms;
+  final List<String> boneNames;
+  final List<String> meshNames;
+
+  final int numFrames;
+
+  BoneAnimation(
+      this.boneTransforms, this.boneNames, this.meshNames, this.numFrames);
+
+  Iterable<double> toFrameData() sync* {
+    for (int i = 0; i < numFrames; i++) {
+      for (int j = 0; j < boneTransforms.length; j++) {
+        yield* boneTransforms[j].getFrameData(i);
+      }
+    }
+  }
+}