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    标题：10.5 使用SurfaceView绘制动态图像

    实例 SurfaceViewDrawDemo 绘制的是一幅静态图像，而使用 SurfaceView 可以绘制动态图像。

    绘制动态图像的过程应该在一个单独的线程中完成，而不应该在主线程中进行。实例 SurfaceViewDynDrawDemo 演示了使用 SurfaceView 组件绘制动态图像的过程。

    该实例修改自 Android SDK 提供的实例，绘制的是类似于 Windows 中的变幻线屏保的效果，运行效果如图 1 所示。
    实例SurfaceViewDynDrawDemo的运行效果
    图 1  实例 SurfaceViewDynDrawDemo 的运行效果

    实例 SurfaceViewDynDrawDemo 的布局文件 main.xml 内容如下： 
    1. <?xml version="1.0" encoding="utf-8"?>
    2.  
    3. <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    4.     android:layout_width="fill_parent"
    5.     android:layout_height="fill_parent"
    6.     android:orientation="vertical">
    7.  
    8.     <TextView
    9.         android:layout_width="fill_parent"
    10.         android:layout_height="wrap_content"
    11.         android:text="@string/hello" />
    12.  
    13.     <SurfaceView
    14.         android:id="@+id/surfaceViewl"
    15.         android:layout_width="fill_parent"
    16.         android:layout_height="fill_parent" />
    17.   
    18. </LinearLayout>
    实例 SurfaceViewDynDrawDemo 的主 Activity 为 SurfaceViewDynDrawDemoActivity，其代码如下： 
    1. import android.app.Activity;
    2. import android.graphics.Canvas;
    3. import android.graphics.Paint;
    4. import android.os.Bundle;
    5. import android.util.Log;
    6. import android.view.SurfaceHolder;
    7. import android.view.SurfaceView;
    8.  
    9. public class SurfaceViewDynDrawDemoActivity extends Activity {
    10.     private SurfaceView mySurfaceView;
    11.     private DrawingThread mDrawingThread;
    12.     SurfaceHolder surfaceHolder;
    13.  
    14.     /**
    15.      * Called when the activity is first created.
    16.      */
    17.     @Override
    18.     public void onCreate(Bundle savedInstanceState) {
    19.         super.onCreate(savedInstanceState);
    20.         setContentView(R.layout.main);
    21.         mySurfaceView = (SurfaceView) findViewById(R.id.surfaceViewl);
    22.         surfaceHolder = mySurfaceView.getHolder();
    23.         surfaceHolder.addCallback(new SurfaceHolder.Callback() {
    24.  
    25.             @Override
    26.             public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
    27.                 // TODO Auto-generated method stub
    28.             }
    29.  
    30.             @Override
    31.             public void surfaceCreated(SurfaceHolder holder) {
    32.                 // TODO Auto-generated method stub
    33.                 mDrawingThread = new DrawingThread();
    34.                 mDrawingThread.mSurface = surfaceHolder;
    35.                 mDrawingThread.start();
    36.             }
    37.  
    38.             @Override
    39.             public void surfaceDestroyed(SurfaceHolder holder) {
    40.                 // TODO Auto-generated method stub
    41.                 mDrawingThread.mQuit = true;
    42.             }
    43.         });
    44.     }
    45.  
    46.     static final class MovingPoint {
    47.         float x, y, dx, dy;
    48.  
    49.         void init(int width, int height, float minStep) {
    50.             x = (float) ((width - 1) * Math.random());
    51.             y = (float) ((height - 1) * Math.random());
    52.             dx = (float) (Math.random() * minStep * 2) + 1;
    53.             dy = (float) (Math.random() * minStep * 2) + 1;
    54.         }
    55.  
    56.         float adjDelta(float cur, float minStep, float maxStep) {
    57.             cur += (Math.random() * minStep) - (minStep / 2);
    58.             if (cur < 0 && cur > -minStep) cur = -minStep;
    59.             if (cur >= 0 && cur < minStep) cur = minStep;
    60.             if (cur > maxStep) cur = maxStep;
    61.             if (cur < -maxStep) cur = -maxStep;
    62.             return cur;
    63.         }
    64.  
    65.         void step(int width, int height, float minStep, float maxStep) {
    66.             x += dx;
    67.             if (x <= 0 || x >= (width - 1)) {
    68.                 if (x <= 0) x = 0;
    69.                 else if (x >= (width - 1)) x = width - 1;
    70.                 dx = adjDelta(-dx, minStep, maxStep);
    71.             }
    72.             y += dy;
    73.             if (y <= 0 || y >= (height - 1)) {
    74.                 if (y <= 0) y = 0;
    75.                 else if (y >= (height - 1)) y = height - 1;
    76.                 dy = adjDelta(-dy, minStep, maxStep);
    77.             }
    78.         }
    79.     }
    80.  
    81.     class DrawingThread extends Thread {
    82.         // These are protected by the Thread's lock
    83.         SurfaceHolder mSurface;
    84.         boolean mRunning;
    85.         boolean mActive;
    86.         boolean mQuit;
    87.         // Internal state
    88.         int mLineWidth;
    89.         float mMinStep;
    90.         float mMaxStep;
    91.  
    92.         boolean mInitialized = false;
    93.         final MovingPoint mPoint1 = new MovingPoint();
    94.         final MovingPoint mPoint2 = new MovingPoint();
    95.  
    96.         static final int NUM_OLD = 100;
    97.         int mNum0ld = 0;
    98.         final float[] m0ld = new float[NUM_OLD * 4];
    99.         final int[] m01dColor = new int[NUM_OLD];
    100.         int mBrightLine = 0;
    101.  
    102.         // X is red, Y is blue
    103.         final MovingPoint mColor = new MovingPoint();
    104.  
    105.         final Paint mBackground = new Paint();
    106.         final Paint mForeground = new Paint();
    107.  
    108.         int makeGreen(int index) {
    109.             int dist = Math.abs(mBrightLine - index);
    110.             if (dist > 10) return 0;
    111.             return (255 - (dist * (255 / 10))) << 8;
    112.         }
    113.  
    114.         @Override
    115.         public void run() {
    116.             mLineWidth = (int

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