createBitmap方法能够截取源位图不同位置的块，实现游戏背景的移动

public class MainActivity extends Activity {

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(new MyView(MainActivity.this));

}

class MyView extends View{

//背景图实际高度

final int BACK_HEIGHT=1700;

//背景图和飞机

private Bitmap back;

private Bitmap plane;

final int WIDTH=640,HEIGHT=880;

//Matrix实例用于控制缩放

private Matrix matrix=new Matrix();

//图片开始的Y坐标

private int StartY=BACK_HEIGHT-HEIGHT;

public MyView(Context context) {

super(context);

back=BitmapFactory.decodeResource(context.getResources(), R.drawable.back_img);

//获取窗口管理器

WindowManager windowManager=getWindowManager();

Display display=windowManager.getDefaultDisplay();

DisplayMetrics metrics=new DisplayMetrics();

display.getMetrics(metrics);

//获得屏幕宽度

float screenWidth=metrics.widthPixels;

//确定缩放比例

float scale=screenWidth/WIDTH;

matrix.setScale(scale, scale);

plane=BitmapFactory.decodeResource(context.getResources(), R.drawable.plane);

final Handler handler=new Handler(){

@Override

public void handleMessage(Message msg) {

if(msg.what==0x123){

//图片向上移动/回到初始状态

if(StartY<3){

StartY=BACK_HEIGHT-HEIGHT;

}else{

StartY-=3;

}

}

//通知VIew重绘(调用OnDraw方法)

invalidate();

}

};

//每100ms移动一次

new Timer().schedule(new TimerTask() {

@Override

public void run() {

// TODO Auto-generated method stub

handler.sendEmptyMessage(0x123);

}

}, 0,100);

}

@Override

protected void onDraw(Canvas canvas) {

//截取背景图的一段作为实际绘制的背景图

Bitmap bitmap2=Bitmap.createBitmap(back,0,StartY,WIDTH,HEIGHT,matrix,false);

canvas.drawBitmap(bitmap2, 0, 0,null);

canvas.drawBitmap(plane, 320,700, null);

}

}