Android Accelerometer app

/*
 * V0.02
 * 9/10/11 - 1315
 * crosshair, text added
 * tried using sensor.TYPE_ORIENTATION, but causes jumps from 0 to 180, which may be   problematic in final version
 * locked to portrait for satmap version.
 * keeps crashing?? not sure why, ddms no help
 */

 package com.saltapps.satmap;

 import android.app.Activity;
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
 import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
 import android.hardware.Sensor;
 import android.hardware.SensorEvent;
 import android.hardware.SensorEventListener;
 import android.hardware.SensorManager;
 import android.os.Bundle;
 import android.view.SurfaceHolder;
import android.view.SurfaceView;

 public class Accelerometer extends Activity  implements SensorEventListener{

    float x, y, vPitch, vRoll;
    Bitmap bubble, crosshair;
    SensorManager sM;
    GFX2Surface ourSurfaceView;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new GFX2Surface(this));

        sM = (SensorManager) getSystemService(Context.SENSOR_SERVICE);

        if (sM.getSensorList(Sensor.TYPE_ACCELEROMETER).size() != 0) {  // checks that phone has accelerometer by making sure SensorList is not empty (=0)
            Sensor s = sM.getSensorList(Sensor.TYPE_ACCELEROMETER).get(0);  // assigns the available accelerometer to variable 's'
            sM.registerListener(this, s, SensorManager.SENSOR_DELAY_NORMAL);    // sets up sensor listener
        }   // if

        bubble = BitmapFactory.decodeResource(getResources(), R.drawable.bubble);
        crosshair = BitmapFactory.decodeResource(getResources(), R.drawable.crosshair);
        x = y = vPitch = vRoll = 0;
        ourSurfaceView = new GFX2Surface(this);
        ourSurfaceView.resume();
        setContentView(ourSurfaceView);

    }   // onCreate


    public class GFX2Surface extends SurfaceView implements Runnable{   // class within a class

        SurfaceHolder ourHolder;
        Thread ourThread = null;
        boolean isRunning = false;

        public GFX2Surface(Context context) {
            super(context);
            ourHolder = getHolder();

        }   // MyBringBackSurface constructor

        public void pause() {
            isRunning = false;
            while(true) {
                try {
                    ourThread.join();   // Blocks the current Thread (Thread.currentThread()) until the receiver finishes its execution and dies
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }   // try/catch
                break;
            }   // while

            ourThread = null;

        }   // pause()

        public void resume() {

            isRunning = true;
            ourThread = new Thread(this);   // refers to run method
            ourThread.start();

        }   // resume

        public void run() {

            while(isRunning) {

                if(!ourHolder.getSurface().isValid())   // if surface is not valid
                    continue;

                Canvas canvas = ourHolder.lockCanvas(); // locks the canvas while we set it up, so no other activities can edit it
                canvas.drawColor(Color.BLACK);          // sets color of canvas

                float centerX = (canvas.getWidth()/2) - (bubble.getWidth()/2);
                float centerY = (canvas.getHeight()/2) - (bubble.getHeight()/2);
                float centerCrossX = (canvas.getWidth()/2) - (crosshair.getWidth()/2);
                float centerCrossY = (canvas.getHeight()/2) - (crosshair.getWidth()/2);

                canvas.drawBitmap(crosshair, centerCrossX , centerCrossY, null);
                canvas.drawBitmap(bubble, centerX - vRoll*20, centerY + vPitch*34, null);   // places ball according to sensor amplified by 20/34 (difference due to screen ratio)

                Paint paint = new Paint();
                paint.setStyle(Paint.Style.FILL);
                paint.setColor(Color.GREEN);
                paint.setTextSize(30);
                paint.setAntiAlias(true);

                canvas.drawText("Pitch: " + (int) (vPitch*10) + "°", 0, 25, paint);
                canvas.drawText("Roll: " + (int) (vRoll*10) + "°", 0, 55, paint);

                ourHolder.unlockCanvasAndPost(canvas);

            }   // while

        }   // run()

    }   // class within a class

    @Override
    protected void onPause() {
        super.onPause();
        sM.unregisterListener(this);
    }   // onPause

    public void onAccuracyChanged(Sensor sensor, int accuracy) {
    }   // onAccuracyChanged

    public void onSensorChanged(SensorEvent event) {

        try {
            Thread.sleep(16);   // Delays to 60 sensor checks per second
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }   // try/catch

        vRoll = event.values[0];
        vPitch = event.values[1];

    }   // onSensorChanged




 }  // class