Attempt to calculate orientation without magnetic field sensor data w…

…hen it's missing.

app/src/main/java/org/thoughtcrime/securesms/components/sensors/DeviceOrientationMonitor.java

@@ -65,7 +65,10 @@ public LiveData<Orientation> getOrientation() {
   }
 
   private void updateOrientationAngles() {
-    SensorManager.getRotationMatrix(rotationMatrix, null, accelerometerReading, magnetometerReading);
+    boolean success = SensorManager.getRotationMatrix(rotationMatrix, null, accelerometerReading, magnetometerReading);
+    if (!success) {
+      SensorUtil.getRotationMatrixWithoutMagneticSensorData(rotationMatrix, accelerometerReading);
+    }
     SensorManager.getOrientation(rotationMatrix, orientationAngles);
 
     float pitch = orientationAngles[1];

app/src/main/java/org/thoughtcrime/securesms/components/sensors/SensorUtil.java

@@ -0,0 +1,92 @@
+package org.thoughtcrime.securesms.components.sensors;
+
+public final class SensorUtil {
+
+  private SensorUtil() { }
+
+  public static void getRotationMatrixWithoutMagneticSensorData(float[] rotationMatrix, float[] accelerometerReading) {
+    double gx, gy, gz;
+    gx = accelerometerReading[0] / 9.81f;
+    gy = accelerometerReading[1] / 9.81f;
+    gz = accelerometerReading[2] / 9.81f;
+
+    float pitch   = (float) -Math.atan(gy / Math.sqrt(gx * gx + gz * gz));
+    float roll    = (float) -Math.atan(gx / Math.sqrt(gy * gy + gz * gz));
+    float azimuth = 0;
+
+    float[] fakeMagnetometerReading = { azimuth, pitch, roll };
+
+    System.arraycopy(getRotationMatrixForOrientation(fakeMagnetometerReading), 0, rotationMatrix, 0, rotationMatrix.length);
+  }
+
+  private static float[] getRotationMatrixForOrientation(float[] o) {
+    float[] xM = new float[9];
+    float[] yM = new float[9];
+    float[] zM = new float[9];
+
+    float sinX = (float) Math.sin(o[1]);
+    float cosX = (float) Math.cos(o[1]);
+    float sinY = (float) Math.sin(o[2]);
+    float cosY = (float) Math.cos(o[2]);
+    float sinZ = (float) Math.sin(o[0]);
+    float cosZ = (float) Math.cos(o[0]);
+
+    xM[0] = 1.0f;
+    xM[1] = 0.0f;
+    xM[2] = 0.0f;
+
+    xM[3] = 0.0f;
+    xM[4] = cosX;
+    xM[5] = sinX;
+
+    xM[6] = 0.0f;
+    xM[7] = -sinX;
+    xM[8] = cosX;
+
+    yM[0] = cosY;
+    yM[1] = 0.0f;
+    yM[2] = sinY;
+
+    yM[3] = 0.0f;
+    yM[4] = 1.0f;
+    yM[5] = 0.0f;
+
+    yM[6] = -sinY;
+    yM[7] = 0.0f;
+    yM[8] = cosY;
+
+    zM[0] = cosZ;
+    zM[1] = sinZ;
+    zM[2] = 0.0f;
+
+    zM[3] = -sinZ;
+    zM[4] = cosZ;
+    zM[5] = 0.0f;
+
+    zM[6] = 0.0f;
+    zM[7] = 0.0f;
+    zM[8] = 1.0f;
+
+    float[] resultMatrix = matrixMultiplication(xM, yM);
+    resultMatrix = matrixMultiplication(zM, resultMatrix);
+    return resultMatrix;
+  }
+
+  private static float[] matrixMultiplication(float[] A, float[] B) {
+    float[] result = new float[9];
+
+    result[0] = A[0] * B[0] + A[1] * B[3] + A[2] * B[6];
+    result[1] = A[0] * B[1] + A[1] * B[4] + A[2] * B[7];
+    result[2] = A[0] * B[2] + A[1] * B[5] + A[2] * B[8];
+
+    result[3] = A[3] * B[0] + A[4] * B[3] + A[5] * B[6];
+    result[4] = A[3] * B[1] + A[4] * B[4] + A[5] * B[7];
+    result[5] = A[3] * B[2] + A[4] * B[5] + A[5] * B[8];
+
+    result[6] = A[6] * B[0] + A[7] * B[3] + A[8] * B[6];
+    result[7] = A[6] * B[1] + A[7] * B[4] + A[8] * B[7];
+    result[8] = A[6] * B[2] + A[7] * B[5] + A[8] * B[8];
+
+    return result;
+  }
+}