Android自学之图形图像之使用双缓冲画

参考文章：http://blog.youkuaiyun.com/lee576/article/details/7870160

在他的基础上稍微补充了一点：

当数据量很大时，绘图可能需要几秒钟甚至更长的时间，而且有时还会出现闪烁现象，为了解决这些问题，可采用双缓冲技术来绘图。
　双缓冲即在内存中创建一个与屏幕绘图区域一致的对象，先将图形绘制到内存中的这个对象上，再一次性将这个对象上的图形拷贝到屏幕上，这样能大大加快绘图的速度。双缓冲实现过程如下：
　　1、在内存中创建与画布一致的缓冲区
　　2、在缓冲区画图
　　3、将缓冲区位图拷贝到当前画布上

　　4、释放内存缓冲区

代码已经传到网上，下载地址为：

http://download.youkuaiyun.com/download/qizheguang/9434947

下面贴代码：

MainActivity.java

package com.example.doublebuffer;

import android.os.Bundle;
import android.app.Activity;
import android.graphics.BlurMaskFilter;
import android.graphics.EmbossMaskFilter;
import android.graphics.Color;  
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class MainActivity extends Activity{

	 EmbossMaskFilter emboss;  
	 BlurMaskFilter blur;
	
	 DrawView	drawview;			//调用另一个类
	 
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		emboss = new EmbossMaskFilter(new float[]{1.5f,1.5f,1.5f},0.6f,6,4.2f);  
        blur = new BlurMaskFilter(8,BlurMaskFilter.Blur.NORMAL); 
        
        Button button = (Button)findViewById(R.id.Erase_Everything);
        
        drawview = (DrawView)findViewById(R.id.draw);
        
        button.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				drawview.ReleaseDraw();	
			}
		});
	}
	
	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		
		MenuInflater inflator = new MenuInflater(this);  
        //状态R.menu.context对应菜单,并添加到中  
        inflator.inflate(R.menu.main, menu);  
        return super.onCreateOptionsMenu(menu);  
        
        
//		getMenuInflater().inflate(R.menu.main, menu);
//		return true;
	}

	
	//菜单项被单击后的回调方法  
	@Override
    public boolean onOptionsItemSelected(MenuItem mi)  
    {  
        DrawView dv = (DrawView)findViewById(R.id.draw);  
        //判断单击的是哪个菜单项,并有针对性地做出响应  
        switch(mi.getItemId())  
        {  
            case R.id.red:  
                dv.paint.setColor(Color.RED);  
                mi.setChecked(true);  
                break;  
            case R.id.green:  
                dv.paint.setColor(Color.GREEN);  
                mi.setChecked(true);  
                break;  
            case R.id.blue:  
                dv.paint.setColor(Color.BLUE);  
                mi.setChecked(true);  
                break;  
            case R.id.width_1:  
                dv.paint.setStrokeWidth(1);  
                mi.setChecked(true);  
                break;  
            case R.id.width_3:  
                dv.paint.setStrokeWidth(3);  
                mi.setChecked(true);  
                break;  
            case R.id.width_5:  
                dv.paint.setStrokeWidth(5);  
                mi.setChecked(true);  
                break;  
            case R.id.blur:  
                dv.paint.setMaskFilter(blur);  
                mi.setChecked(true);  
                break;  
            case R.id.emboss:  
                dv.paint.setMaskFilter(emboss);  
                mi.setChecked(true);  
                break;
        }  
        return true;  
    }  
    
}

DrawView.java

package com.example.doublebuffer;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Path;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.WindowManager;
import android.view.ViewGroup.LayoutParams;
import android.widget.Button;

public class DrawView extends View {
	
//	public Button btnEraseAll;
//  public LayoutParams params;
    
	float preX;  
    float preY;  
    private Path path;  
    public Paint paint = null;  
//    final int VIEW_WIDTH = 320;  
 //   final int VIEW_HEIGHT = 480;  
    //定义一个内存中的图片,该图片将作为缓冲区  
    Bitmap cacheBitmap = null;  
    //定义cacheBitmap上的canvas对象  
    Canvas cacheCanvas = null;  
    int width;								//手机屏幕宽度
    int height;								//手机屏幕高度
    
    public DrawView(Context context, AttributeSet attrs) {  
        super(context, attrs);  
        //创建一个与该View相同大小的缓存区  
 //      cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH,VIEW_HEIGHT,Config.ARGB_8888);
    	
       WindowManager wm = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
       width = wm.getDefaultDisplay().getWidth();			//--表示函数很老
       height = wm.getDefaultDisplay().getHeight();
        
//      btnEraseAll = new Button(context);
//      btnEraseAll.setText("Erase Everything!!");
//      params = new LayoutParams(LayoutParams.MATCH_PARENT,LayoutParams.WRAP_CONTENT);			//动态构建布局
//      btnEraseAll.setLayoutParams(params);
           	
    } 
    
    //释放
    public void ReleaseDraw()
	{	
    	cacheBitmap = null;
    	cacheCanvas = null;
    	
		path.reset();
		postInvalidate();  
	}
    
    public boolean onTouchEvent(MotionEvent event)  
    {  
        //获取拖动事件发生的位置  
        float x = event.getX();  
        float y = event.getY();  
        switch(event.getAction())  
        {  
            case MotionEvent.ACTION_DOWN:  					//按下
                 path.moveTo(x, y);  
                 preX = x;  
                 preY = y;  
                 break;  
            case MotionEvent.ACTION_MOVE:  					//移动
                 path.quadTo(preX, preY, x, y);  
                 preX = x;  
                 preY = y;  
                 break;  
            case MotionEvent.ACTION_UP:  					//抬起
                 cacheCanvas.drawPath(path, paint);  
                 path.reset();  
                 break;  
        }  
        
        invalidate(); 
        
        //返回true表明处理方法已经处理该事件  
        return true;  
    }
    
    public void onDraw(Canvas canvas)  
    {  
    	if (cacheBitmap == null) {
    		cacheBitmap = Bitmap.createBitmap(width, height, Config.ARGB_8888);  
            cacheCanvas = new Canvas();  
            path = new Path();  
            //设置cacheCanvas将会绘制到内存中的cacheBitmap上  
            cacheCanvas.setBitmap(cacheBitmap);  
            
            //设置画笔的颜色  
            paint = new Paint(Paint.DITHER_FLAG);  
            paint.setColor(Color.RED);  
            
            //设置画笔的风格  
            paint.setStyle(Paint.Style.STROKE);  
            paint.setStrokeWidth(5);  
            
            //设置结合处的样子，MITER:结合处为锐角， ROUND:结合处为圆弧：BEVEL：结合处为直线。
            paint.setStrokeJoin(Paint.Join.ROUND);
            
            //反锯齿  
            paint.setAntiAlias(true);  
            paint.setDither(true);  
		}
    	
        Paint bmpPaint = new Paint();  
        //将cacheBitmap绘制到该View组件上  
        canvas.drawBitmap(cacheBitmap, 0, 0, bmpPaint);  
        //沿着path绘制  
        canvas.drawPath(path, paint);  
    } 
}

布局文件：

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" >

    <LinearLayout
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
         
    <com.example.doublebuffer.DrawView
        android:id="@+id/draw"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="9"
      />
    
    <Button
		android:id="@+id/Erase_Everything"
		android:layout_width="match_parent"
		android:layout_height="0dp"
		android:layout_weight="1"
		android:text="Erase Everything"
		/>
    
    <!-- View 
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:background="#000000"/-->
    </LinearLayout>   
     
</LinearLayout>

menu菜单文件：

main.xml

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

    <!-- item
        android:id="@+id/action_settings"
        android:orderInCategory="100"
        android:showAsAction="never"
        android:title="@string/action_settings"/-->

        <item android:title="@string/color">  
        <menu>  
            <!-- 定义一组单选菜单项 -->  
            <group android:checkableBehavior="single">  
                <!-- 定义多个菜单项 -->  
                <item  
                    android:id="@+id/red" android:title="@string/color_red"/>  
                <item  
                    android:id="@+id/green" android:title="@string/color_green"/>  
                <item  
                    android:id="@+id/blue" android:title="@string/color_blue"/>  
            </group>  
        </menu>  
    </item>  
    <item android:title="@string/width">  
        <menu>  
            <!-- 定义一组菜单项 -->  
            <group>  
                <!-- 定义3个菜单项 -->  
                <item  
                    android:id="@+id/width_1" android:title="@string/width_1"/>  
                <item  
                    android:id="@+id/width_3" android:title="@string/width_3"/>  
                <item  
                    android:id="@+id/width_5" android:title="@string/width_5"/>                        
            </group>  
        </menu>  
    </item>  
    <item  
        android:id="@+id/blur" android:title="@string/blur"/>      
    <item  
        android:id="@+id/emboss" android:title="@string/emboss"/> 
        
</menu>

strings.xml

    <string name="hello">Hello World, HandDraw!</string> 
    <string name="width_1">1像素</string>   
	<string name="width_3">3像素</string>   
	<string name="width_5">5像素</string>   
	<string name="color_red">红色</string>   
	<string name="color_green">绿色</string>   
	<string name="color_blue">蓝色</string>   
	<string name="color">画笔颜色</string>   
	<string name="width">画笔宽度</string>   
	<string name="blur">模糊效果</string>   
	<string name="emboss">浮雕效果</string>