初学Android,图形图像之使用双缓冲画图(二十七)

　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

下面的例子(一个画图板)将实现双缓冲画图

先自定义一个View(Bitmap将会绘制到这个View上)

package Wangli.Graphics.HandDraw;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;public class DrawView extends View {    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;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);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(1);//反锯齿paint.setAntiAlias(true);paint.setDither(true);}    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:         path.moveTo(x, y);         preX = x;         preY = y;         break;        case MotionEvent.ACTION_MOVE:            path.quadTo(preX, preY, x, y);            preX = x;            preY = y;            break;        case MotionEvent.ACTION_UP:         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)    {    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);    }}

定义菜单资源文件my_menu

<?xml version="1.0" encoding="utf-8"?><menu xmlns:android="http://schemas.android.com/apk/res/android"><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 --><itemandroid:id="@+id/red" android:title="@string/color_red"/><itemandroid:id="@+id/green" android:title="@string/color_green"/><itemandroid: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 --><itemandroid:id="@+id/width_1" android:title="@string/width_1"/><itemandroid:id="@+id/width_3" android:title="@string/width_3"/><itemandroid:id="@+id/width_5" android:title="@string/width_5"/></group></menu></item><itemandroid:id="@+id/blur" android:title="@string/blur"/><itemandroid:id="@+id/emboss" android:title="@string/emboss"/></menu>

strings.xml

<?xml version="1.0" encoding="utf-8"?><resources>  <string name="hello">Hello World, HandDraw!</string>   <string name="app_name">手绘</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> </resources>

主界面处理菜单事件　

package Wangli.Graphics.HandDraw;import android.app.Activity;import android.graphics.BlurMaskFilter;import android.graphics.Color;import android.graphics.EmbossMaskFilter;import android.os.Bundle;import android.view.Menu;import android.view.MenuInflater;import android.view.MenuItem;public class HandDraw extends Activity {    /** Called when the activity is first created. */EmbossMaskFilter emboss;BlurMaskFilter blur;    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);        emboss = new EmbossMaskFilter(new float[]{1.5f,1.5f,1.5f},0.6f,6,4.2f);        blur = new BlurMaskFilter(8,BlurMaskFilter.Blur.NORMAL);    }    //负责创建选项菜单    public boolean onCreateOptionsMenu(Menu menu)    {    MenuInflater inflator = new MenuInflater(this);    //状态R.menu.context对应菜单,并添加到中    inflator.inflate(R.menu.my_menu,menu);    return super.onCreateOptionsMenu(menu);    }    //菜单项被单击后的回调方法    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;    }}

下面是实现效果

更改画笔效果