Android 的 SurfaceView 双缓冲应用

鉴客发布于 2010年11月08日 21时 (1评) ?)

双缓冲是为了防止动画闪烁而实现的一种多线程应用，基于SurfaceView的双缓冲实现很简单，开一条线程并在其中绘图即可。本文介绍基于SurfaceView的双缓冲实现，以及介绍类似的更高效的实现方法。

本文程序运行截图如下，左边是开单个线程读取并绘图，右边是开两个线程，一个专门读取图片，一个专门绘图：

对比一下，右边动画的帧速明显比左边的快，左右两者都没使用Thread.sleep()。为什么要开两个线程一个读一个画，而不去开两个线程像左边那样都 “边读边画”呢？因为SurfaceView每次绘图都会锁定Canvas,也就是说同一片区域这次没画完下次就不能画，因此要提高双缓冲的效率，就得开一条线程专门画图，开另外一条线程做预处理的工作。

标签： Android SDK , SurfaceView , 双缓冲

代码片段(3)

[图片] 程序运行截图

[代码] main.xml

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<?xml version="1.0" encoding="utf-8"?> 

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<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

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    android:layout_width="fill_parent" android:layout_height="fill_parent"

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    android:orientation="vertical"> 

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    <LinearLayout android:id="@+id/LinearLayout01"

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        android:layout_width="wrap_content" android:layout_height="wrap_content"> 

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        <Button android:id="@+id/Button01" android:layout_width="wrap_content"

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            android:layout_height="wrap_content" android:text="单个独立线程"></Button> 

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        <Button android:id="@+id/Button02" android:layout_width="wrap_content"

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            android:layout_height="wrap_content" android:text="两个独立线程"></Button> 

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    </LinearLayout> 

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    <SurfaceView android:id="@+id/SurfaceView01"

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        android:layout_width="fill_parent" android:layout_height="fill_parent"></SurfaceView> 

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</LinearLayout>

[代码] TestSurfaceView.java

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package com.testSurfaceView; 

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import java.lang.reflect.Field; 

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import java.util.ArrayList; 

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import android.app.Activity; 

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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.Paint; 

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import android.graphics.Rect; 

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import android.os.Bundle; 

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import android.util.Log; 

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import android.view.SurfaceHolder; 

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import android.view.SurfaceView; 

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import android.view.View; 

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import android.widget.Button; 

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public class TestSurfaceView extends Activity { 

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    /** Called when the activity is first created. */

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    Button btnSingleThread, btnDoubleThread; 

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    SurfaceView sfv; 

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    SurfaceHolder sfh; 

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    ArrayList<Integer> imgList = new ArrayList<Integer>(); 

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    int imgWidth, imgHeight; 

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    Bitmap bitmap;//独立线程读取，独立线程绘图 

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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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        setContentView(R.layout.main); 

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        btnSingleThread = (Button) this.findViewById(R.id.Button01); 

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        btnDoubleThread = (Button) this.findViewById(R.id.Button02); 

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        btnSingleThread.setOnClickListener(new ClickEvent()); 

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        btnDoubleThread.setOnClickListener(new ClickEvent()); 

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        sfv = (SurfaceView) this.findViewById(R.id.SurfaceView01); 

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        sfh = sfv.getHolder(); 

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        sfh.addCallback(new MyCallBack());// 自动运行surfaceCreated以及surfaceChanged 

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    } 

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    class ClickEvent implements View.OnClickListener { 

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        @Override

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        public void onClick(View v) { 

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            if (v == btnSingleThread) { 

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                new Load_DrawImage(0, 0).start();//开一条线程读取并绘图 

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            } else if (v == btnDoubleThread) { 

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                new LoadImage().start();//开一条线程读取 

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                new DrawImage(imgWidth + 10, 0).start();//开一条线程绘图 

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            } 

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        } 

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    } 

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    class MyCallBack implements SurfaceHolder.Callback { 

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        @Override

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        public void surfaceChanged(SurfaceHolder holder, int format, int width, 

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                int height) { 

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            Log.i("Surface:", "Change"); 

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        } 

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        @Override

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        public void surfaceCreated(SurfaceHolder holder) { 

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            Log.i("Surface:", "Create"); 

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            // 用反射机制来获取资源中的图片ID和尺寸 

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            Field[] fields = R.drawable.class.getDeclaredFields(); 

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            for (Field field : fields) { 

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                if (!"icon".equals(field.getName()))// 除了icon之外的图片 

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                { 

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                    int index = 0; 

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                    try { 

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                        index = field.getInt(R.drawable.class); 

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                    } catch (IllegalArgumentException e) { 

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                        // TODO Auto-generated catch block 

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                        e.printStackTrace(); 

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                    } catch (IllegalAccessException e) { 

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                        // TODO Auto-generated catch block 

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                        e.printStackTrace(); 

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                    } 

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                    // 保存图片ID 

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                    imgList.add(index); 

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                } 

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            } 

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            // 取得图像大小 

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            Bitmap bmImg = BitmapFactory.decodeResource(getResources(), 

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                    imgList.get(0)); 

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            imgWidth = bmImg.getWidth(); 

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            imgHeight = bmImg.getHeight(); 

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        } 

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        @Override

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        public void surfaceDestroyed(SurfaceHolder holder) { 

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            Log.i("Surface:", "Destroy"); 

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        } 

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    } 

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    /** 

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     * 读取并显示图片的线程 

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     */

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    class Load_DrawImage extends Thread { 

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        int x, y; 

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        int imgIndex = 0; 

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        public Load_DrawImage(int x, int y) { 

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            this.x = x; 

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            this.y = y; 

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        } 

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        public void run() { 

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            while (true) { 

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                Canvas c = sfh.lockCanvas(new Rect(this.x, this.y, this.x 

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                        + imgWidth, this.y + imgHeight)); 

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                Bitmap bmImg = BitmapFactory.decodeResource(getResources(), 

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                        imgList.get(imgIndex)); 

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                c.drawBitmap(bmImg, this.x, this.y, new Paint()); 

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                imgIndex++; 

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                if (imgIndex == imgList.size()) 

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                    imgIndex = 0; 

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                sfh.unlockCanvasAndPost(c);// 更新屏幕显示内容 

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            } 

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        } 

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    }; 

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    /** 

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     * 只负责绘图的线程 

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     */

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    class DrawImage extends Thread { 

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        int x, y; 

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        public DrawImage(int x, int y) { 

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            this.x = x; 

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            this.y = y; 

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        } 

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        public void run() { 

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            while (true) { 

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                if (bitmap != null) {//如果图像有效 

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                    Canvas c = sfh.lockCanvas(new Rect(this.x, this.y, this.x 

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                            + imgWidth, this.y + imgHeight)); 

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                    c.drawBitmap(bitmap, this.x, this.y, new Paint()); 

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                    sfh.unlockCanvasAndPost(c);// 更新屏幕显示内容 

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                } 

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            } 

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        } 

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    }; 

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    /** 

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     * 只负责读取图片的线程 

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     */

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    class LoadImage extends Thread { 

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        int imgIndex = 0; 

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        public void run() { 

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            while (true) { 

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                bitmap = BitmapFactory.decodeResource(getResources(), 

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                        imgList.get(imgIndex)); 

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                imgIndex++; 

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                if (imgIndex == imgList.size())//如果到尽头则重新读取 

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                    imgIndex = 0; 

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            } 

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        } 

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    }; 

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}