migrate some animation helper classes

lib/animations/bone_driver.dart

@@ -0,0 +1,57 @@
+import 'dart:convert';
+import 'package:vector_math/vector_math.dart';
+import 'package:flutter/foundation.dart';
+import 'package:vector_math/vector_math.dart';
+
+///
+/// Some animation data may be specified as blendshape weights (say, between -1 and 1)
+/// but at runtime we want to retarget this to drive a bone translation/rotation (say, between -pi/2 and pi/2).
+/// A [BoneDriver] is our mechanism for translating the former to the latter, containing:
+/// 1) a blendshape name
+/// 2) a bone name
+/// 3) min/max translation values (corresponding to -1/1 on the blendshape), and
+/// 4) min/max rotation values (corresponding to -1/1 on the blendshape)
+///
+
+class BoneDriver {
+  final String bone;
+  final String blendshape;
+
+  late final Vector3 transMin;
+  late final Vector3 transMax;
+  late final Quaternion rotMin;
+  late final Quaternion rotMax;
+
+  BoneDriver(this.bone, this.blendshape, this.rotMin, this.rotMax,
+      Vector3? transMin, Vector3? transMax) {
+    this.transMin = transMin ?? Vector3.zero();
+    this.transMax = transMax ?? Vector3.zero();
+  }
+
+  factory BoneDriver.fromJsonObject(dynamic jsonObject) {
+    return BoneDriver(
+      jsonObject["bone"],
+      jsonObject["blendshape"],
+      Quaternion.fromFloat32List(Float32List.fromList(jsonObject["rotMin"])),
+      Quaternion.fromFloat32List(Float32List.fromList(jsonObject["rotMax"])),
+      Vector3.fromFloat32List(Float32List.fromList(jsonObject["transMin"])),
+      Vector3.fromFloat32List(Float32List.fromList(jsonObject["transMax"])),
+    );
+  }
+
+  //
+  // Accepts a Float32List containing [numFrames] frames of data for a single morph target weight (for efficiency, this must be unravelled to a single contiguous Float32List).
+  // Returns a generator that yields [numFrames] Quaternions, each representing the (weighted) rotation/translation specified by the mapping of this BoneDriver.
+  //
+  Iterable<Quaternion> transform(List<double> morphTargetFrameData) sync* {
+    for (int i = 0; i < morphTargetFrameData.length; i++) {
+      var weight = (morphTargetFrameData[i] / 2) + 0.5;
+
+      yield Quaternion(
+          rotMin.x + (weight * (rotMax.x - rotMin.x)),
+          rotMin.y + (weight * (rotMax.y - rotMin.y)),
+          rotMin.z + (weight * (rotMax.z - rotMin.z)),
+          1.0);
+    }
+  }
+}