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>