461 lines
17 KiB
Java
461 lines
17 KiB
Java
/*
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* Copyright (C) 2010 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.example.android.accelerometerplay;
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import android.app.Activity;
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import android.content.Context;
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import android.graphics.Bitmap;
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import android.graphics.BitmapFactory;
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import android.graphics.Canvas;
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import android.graphics.BitmapFactory.Options;
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import android.hardware.Sensor;
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import android.hardware.SensorEvent;
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import android.hardware.SensorEventListener;
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import android.hardware.SensorManager;
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import android.os.Bundle;
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import android.os.PowerManager;
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import android.os.PowerManager.WakeLock;
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import android.util.DisplayMetrics;
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import android.view.Display;
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import android.view.Surface;
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import android.view.View;
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import android.view.WindowManager;
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/**
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* This is an example of using the accelerometer to integrate the device's
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* acceleration to a position using the Verlet method. This is illustrated with
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* a very simple particle system comprised of a few iron balls freely moving on
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* an inclined wooden table. The inclination of the virtual table is controlled
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* by the device's accelerometer.
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*
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* @see SensorManager
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* @see SensorEvent
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* @see Sensor
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*/
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public class AccelerometerPlayActivity extends Activity {
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private SimulationView mSimulationView;
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private SensorManager mSensorManager;
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private PowerManager mPowerManager;
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private WindowManager mWindowManager;
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private Display mDisplay;
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private WakeLock mWakeLock;
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/** Called when the activity is first created. */
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@Override
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public void onCreate(Bundle savedInstanceState) {
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super.onCreate(savedInstanceState);
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// Get an instance of the SensorManager
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mSensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
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// Get an instance of the PowerManager
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mPowerManager = (PowerManager) getSystemService(POWER_SERVICE);
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// Get an instance of the WindowManager
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mWindowManager = (WindowManager) getSystemService(WINDOW_SERVICE);
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mDisplay = mWindowManager.getDefaultDisplay();
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// Create a bright wake lock
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mWakeLock = mPowerManager.newWakeLock(PowerManager.SCREEN_BRIGHT_WAKE_LOCK, getClass()
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.getName());
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// instantiate our simulation view and set it as the activity's content
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mSimulationView = new SimulationView(this);
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setContentView(mSimulationView);
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}
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@Override
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protected void onResume() {
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super.onResume();
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/*
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* when the activity is resumed, we acquire a wake-lock so that the
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* screen stays on, since the user will likely not be fiddling with the
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* screen or buttons.
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*/
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mWakeLock.acquire();
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// Start the simulation
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mSimulationView.startSimulation();
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}
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@Override
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protected void onPause() {
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super.onPause();
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/*
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* When the activity is paused, we make sure to stop the simulation,
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* release our sensor resources and wake locks
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*/
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// Stop the simulation
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mSimulationView.stopSimulation();
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// and release our wake-lock
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mWakeLock.release();
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}
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class SimulationView extends View implements SensorEventListener {
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// diameter of the balls in meters
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private static final float sBallDiameter = 0.004f;
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private static final float sBallDiameter2 = sBallDiameter * sBallDiameter;
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// friction of the virtual table and air
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private static final float sFriction = 0.1f;
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private Sensor mAccelerometer;
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private long mLastT;
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private float mLastDeltaT;
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private float mXDpi;
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private float mYDpi;
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private float mMetersToPixelsX;
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private float mMetersToPixelsY;
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private Bitmap mBitmap;
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private Bitmap mWood;
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private float mXOrigin;
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private float mYOrigin;
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private float mSensorX;
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private float mSensorY;
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private long mSensorTimeStamp;
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private long mCpuTimeStamp;
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private float mHorizontalBound;
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private float mVerticalBound;
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private final ParticleSystem mParticleSystem = new ParticleSystem();
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/*
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* Each of our particle holds its previous and current position, its
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* acceleration. for added realism each particle has its own friction
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* coefficient.
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*/
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class Particle {
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private float mPosX;
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private float mPosY;
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private float mAccelX;
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private float mAccelY;
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private float mLastPosX;
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private float mLastPosY;
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private float mOneMinusFriction;
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Particle() {
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// make each particle a bit different by randomizing its
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// coefficient of friction
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final float r = ((float) Math.random() - 0.5f) * 0.2f;
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mOneMinusFriction = 1.0f - sFriction + r;
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}
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public void computePhysics(float sx, float sy, float dT, float dTC) {
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// Force of gravity applied to our virtual object
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final float m = 1000.0f; // mass of our virtual object
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final float gx = -sx * m;
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final float gy = -sy * m;
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/*
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* F = mA <=> A = F / m We could simplify the code by
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* completely eliminating "m" (the mass) from all the equations,
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* but it would hide the concepts from this sample code.
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*/
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final float invm = 1.0f / m;
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final float ax = gx * invm;
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final float ay = gy * invm;
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/*
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* Time-corrected Verlet integration The position Verlet
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* integrator is defined as x(t+dt) = x(t) + x(t) - x(t-dt) +
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* a(t).t^2 However, the above equation doesn't handle variable
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* dt very well, a time-corrected version is needed: x(t+dt) =
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* x(t) + (x(t) - x(t-dt)) * (dt/dt_prev) + a(t).t^2 We also add
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* a simple friction term (f) to the equation: x(t+dt) = x(t) +
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* (1-f) * (x(t) - x(t-dt)) * (dt/dt_prev) + a(t)t^2
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*/
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final float dTdT = dT * dT;
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final float x = mPosX + mOneMinusFriction * dTC * (mPosX - mLastPosX) + mAccelX
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* dTdT;
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final float y = mPosY + mOneMinusFriction * dTC * (mPosY - mLastPosY) + mAccelY
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* dTdT;
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mLastPosX = mPosX;
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mLastPosY = mPosY;
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mPosX = x;
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mPosY = y;
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mAccelX = ax;
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mAccelY = ay;
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}
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/*
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* Resolving constraints and collisions with the Verlet integrator
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* can be very simple, we simply need to move a colliding or
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* constrained particle in such way that the constraint is
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* satisfied.
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*/
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public void resolveCollisionWithBounds() {
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final float xmax = mHorizontalBound;
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final float ymax = mVerticalBound;
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final float x = mPosX;
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final float y = mPosY;
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if (x > xmax) {
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mPosX = xmax;
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} else if (x < -xmax) {
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mPosX = -xmax;
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}
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if (y > ymax) {
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mPosY = ymax;
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} else if (y < -ymax) {
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mPosY = -ymax;
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}
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}
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}
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/*
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* A particle system is just a collection of particles
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*/
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class ParticleSystem {
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static final int NUM_PARTICLES = 15;
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private Particle mBalls[] = new Particle[NUM_PARTICLES];
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ParticleSystem() {
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/*
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* Initially our particles have no speed or acceleration
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*/
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for (int i = 0; i < mBalls.length; i++) {
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mBalls[i] = new Particle();
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}
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}
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/*
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* Update the position of each particle in the system using the
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* Verlet integrator.
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*/
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private void updatePositions(float sx, float sy, long timestamp) {
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final long t = timestamp;
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if (mLastT != 0) {
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final float dT = (float) (t - mLastT) * (1.0f / 1000000000.0f);
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if (mLastDeltaT != 0) {
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final float dTC = dT / mLastDeltaT;
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final int count = mBalls.length;
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for (int i = 0; i < count; i++) {
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Particle ball = mBalls[i];
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ball.computePhysics(sx, sy, dT, dTC);
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}
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}
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mLastDeltaT = dT;
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}
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mLastT = t;
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}
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/*
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* Performs one iteration of the simulation. First updating the
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* position of all the particles and resolving the constraints and
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* collisions.
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*/
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public void update(float sx, float sy, long now) {
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// update the system's positions
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updatePositions(sx, sy, now);
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// We do no more than a limited number of iterations
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final int NUM_MAX_ITERATIONS = 10;
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/*
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* Resolve collisions, each particle is tested against every
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* other particle for collision. If a collision is detected the
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* particle is moved away using a virtual spring of infinite
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* stiffness.
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*/
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boolean more = true;
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final int count = mBalls.length;
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for (int k = 0; k < NUM_MAX_ITERATIONS && more; k++) {
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more = false;
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for (int i = 0; i < count; i++) {
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Particle curr = mBalls[i];
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for (int j = i + 1; j < count; j++) {
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Particle ball = mBalls[j];
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float dx = ball.mPosX - curr.mPosX;
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float dy = ball.mPosY - curr.mPosY;
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float dd = dx * dx + dy * dy;
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// Check for collisions
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if (dd <= sBallDiameter2) {
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/*
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* add a little bit of entropy, after nothing is
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* perfect in the universe.
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*/
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dx += ((float) Math.random() - 0.5f) * 0.0001f;
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dy += ((float) Math.random() - 0.5f) * 0.0001f;
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dd = dx * dx + dy * dy;
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// simulate the spring
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final float d = (float) Math.sqrt(dd);
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final float c = (0.5f * (sBallDiameter - d)) / d;
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curr.mPosX -= dx * c;
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curr.mPosY -= dy * c;
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ball.mPosX += dx * c;
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ball.mPosY += dy * c;
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more = true;
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}
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}
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/*
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* Finally make sure the particle doesn't intersects
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* with the walls.
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*/
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curr.resolveCollisionWithBounds();
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}
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}
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}
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public int getParticleCount() {
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return mBalls.length;
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}
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public float getPosX(int i) {
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return mBalls[i].mPosX;
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}
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public float getPosY(int i) {
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return mBalls[i].mPosY;
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}
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}
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public void startSimulation() {
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/*
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* It is not necessary to get accelerometer events at a very high
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* rate, by using a slower rate (SENSOR_DELAY_UI), we get an
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* automatic low-pass filter, which "extracts" the gravity component
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* of the acceleration. As an added benefit, we use less power and
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* CPU resources.
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*/
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mSensorManager.registerListener(this, mAccelerometer, SensorManager.SENSOR_DELAY_UI);
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}
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public void stopSimulation() {
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mSensorManager.unregisterListener(this);
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}
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public SimulationView(Context context) {
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super(context);
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mAccelerometer = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
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DisplayMetrics metrics = new DisplayMetrics();
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getWindowManager().getDefaultDisplay().getMetrics(metrics);
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mXDpi = metrics.xdpi;
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mYDpi = metrics.ydpi;
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mMetersToPixelsX = mXDpi / 0.0254f;
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mMetersToPixelsY = mYDpi / 0.0254f;
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// rescale the ball so it's about 0.5 cm on screen
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Bitmap ball = BitmapFactory.decodeResource(getResources(), R.drawable.ball);
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final int dstWidth = (int) (sBallDiameter * mMetersToPixelsX + 0.5f);
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final int dstHeight = (int) (sBallDiameter * mMetersToPixelsY + 0.5f);
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mBitmap = Bitmap.createScaledBitmap(ball, dstWidth, dstHeight, true);
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Options opts = new Options();
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opts.inDither = true;
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opts.inPreferredConfig = Bitmap.Config.RGB_565;
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mWood = BitmapFactory.decodeResource(getResources(), R.drawable.wood, opts);
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}
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@Override
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protected void onSizeChanged(int w, int h, int oldw, int oldh) {
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// compute the origin of the screen relative to the origin of
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// the bitmap
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mXOrigin = (w - mBitmap.getWidth()) * 0.5f;
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mYOrigin = (h - mBitmap.getHeight()) * 0.5f;
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mHorizontalBound = ((w / mMetersToPixelsX - sBallDiameter) * 0.5f);
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mVerticalBound = ((h / mMetersToPixelsY - sBallDiameter) * 0.5f);
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}
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@Override
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public void onSensorChanged(SensorEvent event) {
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if (event.sensor.getType() != Sensor.TYPE_ACCELEROMETER)
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return;
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/*
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* record the accelerometer data, the event's timestamp as well as
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* the current time. The latter is needed so we can calculate the
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* "present" time during rendering. In this application, we need to
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* take into account how the screen is rotated with respect to the
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* sensors (which always return data in a coordinate space aligned
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* to with the screen in its native orientation).
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*/
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switch (mDisplay.getRotation()) {
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case Surface.ROTATION_0:
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mSensorX = event.values[0];
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mSensorY = event.values[1];
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break;
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case Surface.ROTATION_90:
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mSensorX = -event.values[1];
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mSensorY = event.values[0];
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break;
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case Surface.ROTATION_180:
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mSensorX = -event.values[0];
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mSensorY = -event.values[1];
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break;
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case Surface.ROTATION_270:
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mSensorX = event.values[1];
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mSensorY = -event.values[0];
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break;
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}
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mSensorTimeStamp = event.timestamp;
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mCpuTimeStamp = System.nanoTime();
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}
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@Override
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protected void onDraw(Canvas canvas) {
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/*
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* draw the background
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*/
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canvas.drawBitmap(mWood, 0, 0, null);
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/*
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* compute the new position of our object, based on accelerometer
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* data and present time.
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*/
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final ParticleSystem particleSystem = mParticleSystem;
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final long now = mSensorTimeStamp + (System.nanoTime() - mCpuTimeStamp);
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final float sx = mSensorX;
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final float sy = mSensorY;
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particleSystem.update(sx, sy, now);
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final float xc = mXOrigin;
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final float yc = mYOrigin;
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final float xs = mMetersToPixelsX;
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final float ys = mMetersToPixelsY;
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final Bitmap bitmap = mBitmap;
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final int count = particleSystem.getParticleCount();
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for (int i = 0; i < count; i++) {
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/*
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* We transform the canvas so that the coordinate system matches
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* the sensors coordinate system with the origin in the center
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* of the screen and the unit is the meter.
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*/
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final float x = xc + particleSystem.getPosX(i) * xs;
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final float y = yc - particleSystem.getPosY(i) * ys;
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canvas.drawBitmap(bitmap, x, y, null);
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}
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// and make sure to redraw asap
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invalidate();
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}
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@Override
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public void onAccuracyChanged(Sensor sensor, int accuracy) {
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}
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}
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}
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