Android提高第三篇之SurfaceView(下)

http://blog.csdn.net/hellogv/archive/2010/11/04/5986835.aspx
上一篇简单介绍了SurfaceView的使用，这次就介绍SurfaceView的双缓冲使用。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。

main.xml的源码：

<?xml version="1.0" encoding="utf-8"?>  
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    android:layout_width="fill_parent" android:layout_height="fill_parent"  
    android:orientation="vertical">  
  
    <LinearLayout android:id="@+id/LinearLayout01"  
        android:layout_width="wrap_content" android:layout_height="wrap_content">  
        <Button android:id="@+id/Button01" android:layout_width="wrap_content"  
            android:layout_height="wrap_content" android:text="单个独立线程"></Button>  
        <Button android:id="@+id/Button02" android:layout_width="wrap_content"  
            android:layout_height="wrap_content" android:text="两个独立线程"></Button>  
    </LinearLayout>  
    <SurfaceView android:id="@+id/SurfaceView01"  
        android:layout_width="fill_parent" android:layout_height="fill_parent"></SurfaceView>  
</LinearLayout>  

本文程序的源码：

package com.testSurfaceView;  
  
import java.lang.reflect.Field;  
import java.util.ArrayList;  
import android.app.Activity;  
import android.graphics.Bitmap;  
import android.graphics.BitmapFactory;  
import android.graphics.Canvas;  
import android.graphics.Paint;  
import android.graphics.Rect;  
import android.os.Bundle;  
import android.util.Log;  
import android.view.SurfaceHolder;  
import android.view.SurfaceView;  
import android.view.View;  
import android.widget.Button;  
  
public class testSurfaceView extends Activity {  
    /** Called when the activity is first created. */  
    Button btnSingleThread, btnDoubleThread;  
    SurfaceView sfv;  
    SurfaceHolder sfh;  
    ArrayList<Integer> imgList = new ArrayList<Integer>();  
    int imgWidth, imgHeight;  
    Bitmap bitmap;//独立线程读取，独立线程绘图  
  
    @Override  
    public void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.main);  
  
        btnSingleThread = (Button) this.findViewById(R.id.Button01);  
        btnDoubleThread = (Button) this.findViewById(R.id.Button02);  
        btnSingleThread.setOnClickListener(new ClickEvent());  
        btnDoubleThread.setOnClickListener(new ClickEvent());  
        sfv = (SurfaceView) this.findViewById(R.id.SurfaceView01);  
        sfh = sfv.getHolder();  
        sfh.addCallback(new MyCallBack());// 自动运行surfaceCreated以及surfaceChanged  
    }  
  
    class ClickEvent implements View.OnClickListener {  
  
        @Override  
        public void onClick(View v) {  
  
            if (v == btnSingleThread) {  
                new Load_DrawImage(0, 0).start();//开一条线程读取并绘图  
            } else if (v == btnDoubleThread) {  
                new LoadImage().start();//开一条线程读取  
                new DrawImage(imgWidth + 10, 0).start();//开一条线程绘图  
            }  
  
        }  
  
    }  
  
    class MyCallBack implements SurfaceHolder.Callback {  
  
        @Override  
        public void surfaceChanged(SurfaceHolder holder, int format, int width,  
                int height) {  
            Log.i("Surface:", "Change");  
  
        }  
  
        @Override  
        public void surfaceCreated(SurfaceHolder holder) {  
            Log.i("Surface:", "Create");  
  
            // 用反射机制来获取资源中的图片ID和尺寸  
            Field[] fields = R.drawable.class.getDeclaredFields();  
            for (Field field : fields) {  
                if (!"icon".equals(field.getName()))// 除了icon之外的图片  
                {  
                    int index = 0;  
                    try {  
                        index = field.getInt(R.drawable.class);  
                    } catch (IllegalArgumentException e) {  
                        // TODO Auto-generated catch block  
                        e.printStackTrace();  
                    } catch (IllegalAccessException e) {  
                        // TODO Auto-generated catch block  
                        e.printStackTrace();  
                    }  
                    // 保存图片ID  
                    imgList.add(index);  
                }  
            }  
            // 取得图像大小  
            Bitmap bmImg = BitmapFactory.decodeResource(getResources(),  
                    imgList.get(0));  
            imgWidth = bmImg.getWidth();  
            imgHeight = bmImg.getHeight();  
        }  
  
        @Override  
        public void surfaceDestroyed(SurfaceHolder holder) {  
            Log.i("Surface:", "Destroy");  
  
        }  
  
    }  
  
    /* 
     * 读取并显示图片的线程 
     */  
    class Load_DrawImage extends Thread {  
        int x, y;  
        int imgIndex = 0;  
  
        public Load_DrawImage(int x, int y) {  
            this.x = x;  
            this.y = y;  
        }  
  
        public void run() {  
            while (true) {  
                Canvas c = sfh.lockCanvas(new Rect(this.x, this.y, this.x  
                        + imgWidth, this.y + imgHeight));  
                Bitmap bmImg = BitmapFactory.decodeResource(getResources(),  
                        imgList.get(imgIndex));  
                c.drawBitmap(bmImg, this.x, this.y, new Paint());  
                imgIndex++;  
                if (imgIndex == imgList.size())  
                    imgIndex = 0;  
  
                sfh.unlockCanvasAndPost(c);// 更新屏幕显示内容  
            }  
        }  
    };  
  
    /* 
     * 只负责绘图的线程 
     */  
    class DrawImage extends Thread {  
        int x, y;  
  
        public DrawImage(int x, int y) {  
            this.x = x;  
            this.y = y;  
        }  
  
        public void run() {  
            while (true) {  
                if (bitmap != null) {//如果图像有效  
                    Canvas c = sfh.lockCanvas(new Rect(this.x, this.y, this.x  
                            + imgWidth, this.y + imgHeight));  
  
                    c.drawBitmap(bitmap, this.x, this.y, new Paint());  
  
                    sfh.unlockCanvasAndPost(c);// 更新屏幕显示内容  
                }  
            }  
        }  
    };  
  
    /* 
     * 只负责读取图片的线程 
     */  
    class LoadImage extends Thread {  
        int imgIndex = 0;  
  
        public void run() {  
            while (true) {  
                bitmap = BitmapFactory.decodeResource(getResources(),  
                        imgList.get(imgIndex));  
                imgIndex++;  
                if (imgIndex == imgList.size())//如果到尽头则重新读取  
                    imgIndex = 0;  
            }  
        }  
    };  
}