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node_modules/webvr-polyfill/src/sensor-fusion/pose-predictor.js

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+/*
+ * Copyright 2015 Google Inc. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+var MathUtil = require('../math-util');
+var Util = require('../util');
+
+/**
+ * Given an orientation and the gyroscope data, predicts the future orientation
+ * of the head. This makes rendering appear faster.
+ *
+ * Also see: http://msl.cs.uiuc.edu/~lavalle/papers/LavYerKatAnt14.pdf
+ *
+ * @param {Number} predictionTimeS time from head movement to the appearance of
+ * the corresponding image.
+ */
+function PosePredictor(predictionTimeS) {
+  this.predictionTimeS = predictionTimeS;
+
+  // The quaternion corresponding to the previous state.
+  this.previousQ = new MathUtil.Quaternion();
+  // Previous time a prediction occurred.
+  this.previousTimestampS = null;
+
+  // The delta quaternion that adjusts the current pose.
+  this.deltaQ = new MathUtil.Quaternion();
+  // The output quaternion.
+  this.outQ = new MathUtil.Quaternion();
+}
+
+PosePredictor.prototype.getPrediction = function(currentQ, gyro, timestampS) {
+  if (!this.previousTimestampS) {
+    this.previousQ.copy(currentQ);
+    this.previousTimestampS = timestampS;
+    return currentQ;
+  }
+
+  // Calculate axis and angle based on gyroscope rotation rate data.
+  var axis = new MathUtil.Vector3();
+  axis.copy(gyro);
+  axis.normalize();
+
+  var angularSpeed = gyro.length();
+
+  // If we're rotating slowly, don't do prediction.
+  if (angularSpeed < MathUtil.degToRad * 20) {
+    if (Util.isDebug()) {
+      console.log('Moving slowly, at %s deg/s: no prediction',
+                  (MathUtil.radToDeg * angularSpeed).toFixed(1));
+    }
+    this.outQ.copy(currentQ);
+    this.previousQ.copy(currentQ);
+    return this.outQ;
+  }
+
+  // Get the predicted angle based on the time delta and latency.
+  var deltaT = timestampS - this.previousTimestampS;
+  var predictAngle = angularSpeed * this.predictionTimeS;
+
+  this.deltaQ.setFromAxisAngle(axis, predictAngle);
+  this.outQ.copy(this.previousQ);
+  this.outQ.multiply(this.deltaQ);
+
+  this.previousQ.copy(currentQ);
+  this.previousTimestampS = timestampS;
+
+  return this.outQ;
+};
+
+
+module.exports = PosePredictor;