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
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 -->
<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
<?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
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