Add new Android sample app (#190)

This sample app shows a lit, rotating cube

android/filament-android/src/main/cpp/MathUtils.cpp

@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include <jni.h>
+
+#include <math/mat3.h>
+#include <math/quat.h>
+
+using namespace math;
+
+extern "C" JNIEXPORT void JNICALL
+Java_com_google_android_filament_MathUtils_nPackTangentFrame(JNIEnv *env, jclass,
+        jfloat tangentX, jfloat tangentY, jfloat tangentZ,
+        jfloat bitangentX, jfloat bitangentY, jfloat bitangentZ,
+        jfloat normalX, jfloat normalY, jfloat normalZ,
+        jfloatArray quaternion_, jint offset) {
+
+    float3 tangent{tangentX, tangentY, tangentZ};
+    float3 bitangent{bitangentX, bitangentY, bitangentZ};
+    float3 normal{normalX, normalY, normalZ};
+    quatf q = mat3f::packTangentFrame({tangent, bitangent, normal});
+
+    env->SetFloatArrayRegion(quaternion_, offset, 4,
+             reinterpret_cast<jfloat*>(&q));
+}