--- /dev/null
+# Copyright (C) 2010 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.
+#
+
+LOCAL_PATH:= $(call my-dir)
+include $(CLEAR_VARS)
+
+LOCAL_MODULE_TAGS := samples
+
+# Only compile source java files in this apk.
+LOCAL_SRC_FILES := $(call all-java-files-under, src)
+
+LOCAL_PACKAGE_NAME := AccelerometerPlay
+
+LOCAL_SDK_VERSION := current
+
+include $(BUILD_PACKAGE)
+
+# Use the following include to make our test apk.
+include $(call all-makefiles-under,$(LOCAL_PATH))
--- /dev/null
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2010 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.
+-->
+
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+ android:versionCode="1"
+ android:versionName="1.0" package="com.example.android.accelerometerplay">
+ <application android:icon="@drawable/icon" android:label="@string/app_name">
+ <activity android:name=".AccelerometerPlayActivity"
+ android:label="@string/app_name"
+ android:screenOrientation="portrait" android:theme="@android:style/Theme.NoTitleBar.Fullscreen">
+ <intent-filter>
+ <action android:name="android.intent.action.MAIN" />
+ <category android:name="android.intent.category.LAUNCHER" />
+ </intent-filter>
+ </activity>
+
+ </application>
+
+
+<uses-sdk android:minSdkVersion="5"></uses-sdk>
+<uses-permission android:name="android.permission.VIBRATE"></uses-permission>
+
+<uses-permission android:name="android.permission.WAKE_LOCK"></uses-permission>
+
+</manifest>
\ No newline at end of file
--- /dev/null
+
+ Copyright (c) 2005-2008, 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.
+
+ 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.
+
+
+ Apache License
+ Version 2.0, January 2004
+ http://www.apache.org/licenses/
+
+ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+ 1. Definitions.
+
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+ 7. Disclaimer of Warranty. Unless required by applicable law or
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+
+ 8. Limitation of Liability. In no event and under no legal theory,
+ whether in tort (including negligence), contract, or otherwise,
+ unless required by applicable law (such as deliberate and grossly
+ negligent acts) or agreed to in writing, shall any Contributor be
+ liable to You for damages, including any direct, indirect, special,
+ incidental, or consequential damages of any character arising as a
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+
+ END OF TERMS AND CONDITIONS
+
--- /dev/null
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2010 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.
+-->
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+ android:orientation="vertical"
+ android:layout_width="fill_parent"
+ android:layout_height="fill_parent"
+ >
+</LinearLayout>
--- /dev/null
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2010 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.
+-->
+
+<resources>
+ <string name="app_name">AccelerometerPlay</string>
+</resources>
--- /dev/null
+/*
+ * Copyright (C) 2010 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.
+ */
+
+package com.example.android.accelerometerplay;
+
+import android.app.Activity;
+import android.content.Context;
+import android.graphics.Bitmap;
+import android.graphics.BitmapFactory;
+import android.graphics.Canvas;
+import android.graphics.BitmapFactory.Options;
+import android.hardware.Sensor;
+import android.hardware.SensorEvent;
+import android.hardware.SensorEventListener;
+import android.hardware.SensorManager;
+import android.os.Bundle;
+import android.os.PowerManager;
+import android.os.PowerManager.WakeLock;
+import android.util.DisplayMetrics;
+import android.view.View;
+
+/**
+ * This is an example of using the accelerometer to integrate the device's
+ * acceleration to a position using the Verlet method. This is illustrated with
+ * a very simple particle system comprised of a few iron balls freely moving on
+ * an inclined wooden table. The inclination of the virtual table is controlled
+ * by the device's accelerometer.
+ *
+ * @see SensorManager
+ * @see SensorEvent
+ * @see Sensor
+ */
+
+public class AccelerometerPlayActivity extends Activity {
+
+ private SimulationView mSimulationView;
+ private SensorManager mSensorManager;
+ private PowerManager mPowerManager;
+ private WakeLock mWakeLock;
+
+ /** Called when the activity is first created. */
+ @Override
+ public void onCreate(Bundle savedInstanceState) {
+ super.onCreate(savedInstanceState);
+
+ // Get an instance of the SensorManager
+ mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
+
+ // Get an instance of the PowerManager
+ mPowerManager = (PowerManager) getSystemService(POWER_SERVICE);
+
+ // Create a bright wake lock
+ mWakeLock = mPowerManager.newWakeLock(
+ PowerManager.SCREEN_BRIGHT_WAKE_LOCK, getClass().getName());
+
+ // instantiate our simulation view and set it as the activity's content
+ mSimulationView = new SimulationView(this);
+ setContentView(mSimulationView);
+ }
+
+ @Override
+ protected void onResume() {
+ super.onResume();
+ /*
+ * when the activity is resumed, we acquire a wake-lock so that the
+ * screen stays on, since the user will likely not be fiddling with the
+ * screen or buttons.
+ */
+ mWakeLock.acquire();
+
+ // Start the simulation
+ mSimulationView.startSimulation();
+ }
+
+ @Override
+ protected void onPause() {
+ super.onPause();
+ /*
+ * When the activity is paused, we make sure to stop the simulation,
+ * release our sensor resources and wake locks
+ */
+
+ // Stop the simulation
+ mSimulationView.stopSimulation();
+
+ // and release our wake-lock
+ mWakeLock.release();
+ }
+
+ class SimulationView extends View implements SensorEventListener {
+ // diameter of the balls in meters
+ private static final float sBallDiameter = 0.004f;
+ private static final float sBallDiameter2 = sBallDiameter
+ * sBallDiameter;
+
+ // friction of the virtual table and air
+ private static final float sFriction = 0.1f;
+
+ private Sensor mAccelerometer;
+ private long mLastT;
+ private float mLastDeltaT;
+
+ private float mXDpi;
+ private float mYDpi;
+ private float mMetersToPixelsX;
+ private float mMetersToPixelsY;
+ private Bitmap mBitmap;
+ private Bitmap mWood;
+ private float mXOrigin;
+ private float mYOrigin;
+ private float mSensorX;
+ private float mSensorY;
+ private long mSensorTimeStamp;
+ private long mCpuTimeStamp;
+ private float mHorizontalBound;
+ private float mVerticalBound;
+ private final ParticleSystem mParticleSystem = new ParticleSystem();
+
+ /*
+ * Each of our particle holds its previous and current position, its
+ * acceleration. for added realism each particle has its own friction
+ * coefficient.
+ */
+ class Particle {
+ private float mPosX;
+ private float mPosY;
+ private float mAccelX;
+ private float mAccelY;
+ private float mLastPosX;
+ private float mLastPosY;
+ private float mOneMinusFriction;
+
+ Particle() {
+ // make each particle a bit different by randomizing its
+ // coefficient of friction
+ final float r = ((float) Math.random() - 0.5f) * 0.2f;
+ mOneMinusFriction = 1.0f - sFriction + r;
+ }
+
+ public void computePhysics(float sx, float sy, float dT, float dTC) {
+ // Force of gravity applied to our virtual object
+ final float m = 1000.0f; // mass of our virtual object
+ final float gx = -sx * m;
+ final float gy = -sy * m;
+
+ /*
+ * ·F = mA <=> A = ·F / m
+ *
+ * We could simplify the code by completely eliminating "m" (the
+ * mass) from all the equations, but it would hide the concepts
+ * from this sample code.
+ */
+ final float invm = 1.0f / m;
+ final float ax = gx * invm;
+ final float ay = gy * invm;
+
+ /*
+ * Time-corrected Verlet integration
+ *
+ * The position Verlet integrator is defined as
+ *
+ * x(t+Æt) = x(t) + x(t) - x(t-Æt) + a(t)Ætö2
+ *
+ * However, the above equation doesn't handle variable Æt very
+ * well, a time-corrected version is needed:
+ *
+ * x(t+Æt) = x(t) + (x(t) - x(t-Æt)) * (Æt/Æt_prev) + a(t)Ætö2
+ *
+ *
+ * We also add a simple friction term (f) to the equation:
+ *
+ * x(t+Æt) = x(t) + (1-f) * (x(t) - x(t-Æt)) * (Æt/Æt_prev) +
+ * a(t)Ætö2
+ */
+ final float dTdT = dT * dT;
+ final float x = mPosX + mOneMinusFriction * dTC
+ * (mPosX - mLastPosX) + mAccelX * dTdT;
+ final float y = mPosY + mOneMinusFriction * dTC
+ * (mPosY - mLastPosY) + mAccelY * dTdT;
+ mLastPosX = mPosX;
+ mLastPosY = mPosY;
+ mPosX = x;
+ mPosY = y;
+ mAccelX = ax;
+ mAccelY = ay;
+ }
+
+ /*
+ * Resolving constraints and collisions with the Verlet integrator
+ * can be very simple, we simply need to move a colliding or
+ * constrained particle in such way that the constraint is
+ * satisfied.
+ */
+ public void resolveCollisionWithBounds() {
+ final float xmax = mHorizontalBound;
+ final float ymax = mVerticalBound;
+ final float x = mPosX;
+ final float y = mPosY;
+ if (x > xmax) {
+ mPosX = xmax;
+ } else if (x < -xmax) {
+ mPosX = -xmax;
+ }
+ if (y > ymax) {
+ mPosY = ymax;
+ } else if (y < -ymax) {
+ mPosY = -ymax;
+ }
+ }
+ }
+
+ /*
+ * A particle system is just a collection of particles
+ */
+ class ParticleSystem {
+ static final int NUM_PARTICLES = 15;
+ private Particle mBalls[] = new Particle[NUM_PARTICLES];
+
+ ParticleSystem() {
+ /*
+ * Initially our particles have no speed or acceleration
+ */
+ for (int i = 0; i < mBalls.length; i++) {
+ mBalls[i] = new Particle();
+ }
+ }
+
+ /*
+ * Update the position of each particle in the system using the
+ * Verlet integrator.
+ */
+ private void updatePositions(float sx, float sy, long timestamp) {
+ final long t = timestamp;
+ if (mLastT != 0) {
+ final float dT = (float) (t - mLastT)
+ * (1.0f / 1000000000.0f);
+ if (mLastDeltaT != 0) {
+ final float dTC = dT / mLastDeltaT;
+ final int count = mBalls.length;
+ for (int i = 0; i < count; i++) {
+ Particle ball = mBalls[i];
+ ball.computePhysics(sx, sy, dT, dTC);
+ }
+ }
+ mLastDeltaT = dT;
+ }
+ mLastT = t;
+ }
+
+ /*
+ * Performs one iteration of the simulation. First updating the
+ * position of all the particles and resolving the constraints and
+ * collisions.
+ */
+ public void update(float sx, float sy, long now) {
+ // update the system's positions
+ updatePositions(sx, sy, now);
+
+ // We do no more than a limited number of iterations
+ final int NUM_MAX_ITERATIONS = 10;
+
+ /*
+ * Resolve collisions, each particle is tested against every
+ * other particle for collision. If a collision is detected the
+ * particle is moved away using a virtual spring of infinite
+ * stiffness.
+ */
+ boolean more = true;
+ final int count = mBalls.length;
+ for (int k = 0; k < NUM_MAX_ITERATIONS && more; k++) {
+ more = false;
+ for (int i = 0; i < count; i++) {
+ Particle curr = mBalls[i];
+ for (int j = i + 1; j < count; j++) {
+ Particle ball = mBalls[j];
+ float dx = ball.mPosX - curr.mPosX;
+ float dy = ball.mPosY - curr.mPosY;
+ float dd = dx * dx + dy * dy;
+ // Check for collisions
+ if (dd <= sBallDiameter2) {
+ /*
+ * add a little bit of entropy, after nothing is
+ * perfect in the universe.
+ */
+ dx += ((float) Math.random() - 0.5f) * 0.0001f;
+ dy += ((float) Math.random() - 0.5f) * 0.0001f;
+ dd = dx * dx + dy * dy;
+ // simulate the spring
+ final float d = (float) Math.sqrt(dd);
+ final float c = (0.5f * (sBallDiameter - d))
+ / d;
+ curr.mPosX -= dx * c;
+ curr.mPosY -= dy * c;
+ ball.mPosX += dx * c;
+ ball.mPosY += dy * c;
+ more = true;
+ }
+ }
+ /*
+ * Finally make sure the particle doesn't intersects
+ * with the walls.
+ */
+ curr.resolveCollisionWithBounds();
+ }
+ }
+ }
+
+ public int getParticleCount() {
+ return mBalls.length;
+ }
+
+ public float getPosX(int i) {
+ return mBalls[i].mPosX;
+ }
+
+ public float getPosY(int i) {
+ return mBalls[i].mPosY;
+ }
+ }
+
+ public void startSimulation() {
+ /*
+ * It is not necessary to get accelerometer events at a very high
+ * rate, by using a slower rate (SENSOR_DELAY_UI), we get an
+ * automatic low-pass filter, which "extracts" the gravity component
+ * of the acceleration. As an added benefit, we use less power and
+ * CPU resources.
+ */
+ mSensorManager.registerListener(this, mAccelerometer,
+ SensorManager.SENSOR_DELAY_UI);
+ }
+
+ public void stopSimulation() {
+ mSensorManager.unregisterListener(this);
+ }
+
+ public SimulationView(Context context) {
+ super(context);
+ mAccelerometer = mSensorManager
+ .getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
+
+ DisplayMetrics metrics = new DisplayMetrics();
+ getWindowManager().getDefaultDisplay().getMetrics(metrics);
+ mXDpi = metrics.xdpi;
+ mYDpi = metrics.ydpi;
+ mMetersToPixelsX = mXDpi / 0.0254f;
+ mMetersToPixelsY = mYDpi / 0.0254f;
+
+ // rescale the ball so it's about 0.5 cm on screen
+ Bitmap ball = BitmapFactory.decodeResource(getResources(),
+ R.drawable.ball);
+ final int dstWidth = (int) (sBallDiameter * mMetersToPixelsX + 0.5f);
+ final int dstHeight = (int) (sBallDiameter * mMetersToPixelsY + 0.5f);
+ mBitmap = Bitmap
+ .createScaledBitmap(ball, dstWidth, dstHeight, true);
+
+ Options opts = new Options();
+ opts.inDither = true;
+ opts.inPreferredConfig = Bitmap.Config.RGB_565;
+ mWood = BitmapFactory.decodeResource(getResources(),
+ R.drawable.wood, opts);
+ }
+
+ @Override
+ protected void onSizeChanged(int w, int h, int oldw, int oldh) {
+ // compute the origin of the screen relative to the origin of
+ // the bitmap
+ mXOrigin = (w - mBitmap.getWidth()) * 0.5f;
+ mYOrigin = (h - mBitmap.getHeight()) * 0.5f;
+ mHorizontalBound = ((w / mMetersToPixelsX - sBallDiameter) * 0.5f);
+ mVerticalBound = ((h / mMetersToPixelsY - sBallDiameter) * 0.5f);
+ }
+
+ @Override
+ public void onSensorChanged(SensorEvent event) {
+ if (event.sensor.getType() != Sensor.TYPE_ACCELEROMETER)
+ return;
+ /*
+ * record the accelerometer data, the event's timestamp as well as
+ * the current time. The latter is needed so we can calculate the
+ * "present" time during rendering.
+ */
+ mSensorX = event.values[0];
+ mSensorY = event.values[1];
+ mSensorTimeStamp = event.timestamp;
+ mCpuTimeStamp = System.nanoTime();
+ }
+
+ @Override
+ protected void onDraw(Canvas canvas) {
+
+ /*
+ * draw the background
+ */
+
+ canvas.drawBitmap(mWood, 0, 0, null);
+
+ /*
+ * compute the new position of our object, based on accelerometer
+ * data and present time.
+ */
+
+ final ParticleSystem particleSystem = mParticleSystem;
+ final long now = mSensorTimeStamp
+ + (System.nanoTime() - mCpuTimeStamp);
+ final float sx = mSensorX;
+ final float sy = mSensorY;
+
+ particleSystem.update(sx, sy, now);
+
+ final float xc = mXOrigin;
+ final float yc = mYOrigin;
+ final float xs = mMetersToPixelsX;
+ final float ys = mMetersToPixelsY;
+ final Bitmap bitmap = mBitmap;
+ final int count = particleSystem.getParticleCount();
+ for (int i = 0; i < count; i++) {
+ /*
+ * We transform the canvas so that the coordinate system matches
+ * the sensors coordinate system with the origin in the center
+ * of the screen and the unit is the meter.
+ */
+
+ final float x = xc + particleSystem.getPosX(i) * xs;
+ final float y = yc - particleSystem.getPosY(i) * ys;
+ canvas.drawBitmap(bitmap, x, y, null);
+ }
+
+ // and make sure to redraw asap
+ invalidate();
+ }
+
+ @Override
+ public void onAccuracyChanged(Sensor sensor, int accuracy) {
+ }
+ }
+}
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