Android开发之用双缓冲技术绘图

双缓冲技术主要用在画图，动画效果上，其原理就是：将资源先载入到缓冲区，然后再将缓冲区整个载入到View上面去。

双缓冲技术可以有效防止闪烁，提高显示质量。

DrawView.java:

package com.example.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 = 720;

final int VIEW_HEIGHT = 800;

//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 set) {

super(context, set);

// TODO Auto-generated constructor stub

//创建一个与该View同样大小的缓冲区

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);

//设置画笔风格

paint.setStyle(Paint.Style.STROKE);

paint.setStrokeWidth(1);

//反锯齿

paint.setAntiAlias(true);

paint.setDither(true);

}

@Override

public boolean onTouchEvent(MotionEvent event) {

//获取拖动事件发生位置

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();

//表明处理方法已经处理改事件

return true;

}

@Override

protected 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);

}

}

my_menu.xml:

<?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 >

            <!-- 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 >

            <!-- 定义三个菜单项 -->

            <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>

Activity.java:

package com.example.handdraw;


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


public class MainActivity extends Activity {

EmbossMaskFilter emboss;
BlurMaskFilter blur;


@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);
}


@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);
inflator.inflate(R.menu.my_menu, menu);
return super.onCreateOptionsMenu(menu);
}


@Override
public boolean onOptionsItemSelected(MenuItem item) {
// TODO Auto-generated method stub
DrawView dv = (DrawView)findViewById(R.id.draw);
switch(item.getItemId())
{
case R.id.red:
dv.paint.setColor(Color.RED);
item.setChecked(true);
break;
case R.id.green:
dv.paint.setColor(Color.GREEN);
item.setChecked(true);
break;
case R.id.blue:
dv.paint.setColor(Color.BLUE);
item.setChecked(true);
break;
case R.id.width_1:
dv.paint.setStrokeWidth(1);
break;
case R.id.width_3:
dv.paint.setStrokeWidth(3);
break;
case R.id.width_5:
dv.paint.setStrokeWidth(5);
break;
case R.id.blur:
dv.paint.setMaskFilter(blur);
break;
case R.id.emboss:
dv.paint.setMaskFilter(emboss);
break;
}
return true;
}
}

main.xml

<RelativeLayout 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"

    android:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"

    android:paddingRight="@dimen/activity_horizontal_margin"

    android:paddingTop="@dimen/activity_vertical_margin"

    tools:context=".MainActivity" >

    <com.example.handdraw.DrawView

        android:id="@+id/draw"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="@string/hello_world" />

</RelativeLayout>