Android采用双缓冲实现画板

Bertha 。 2022-08-21 09:39 144阅读 0赞

## 1.双缓冲技术的概念 ##

所谓的双缓冲技术其实很简单，当程序需要在指定的View上进行绘制时，程序并不需要直接绘制到该View组件，而是先绘制到一个内存中的Bitmap图片上（就是缓冲），等内存中的Bitmap绘制好之后，再一次性将Bitmap绘制到View组件上。

## 2.Android采用双缓冲实现画板 ##

### 2.1 实现的思路： ###

1.定义一个内存中图片，将他作为缓冲区Bitmap cacheBitmap = null;  
2.定义缓冲区Cache的Canvas对象 Canvas cacheCanvas = null;  
3.设置cacheCanvas将会绘制到内存的bitmap上。  
cacheCanvas.setBitmap(cacheBitmap);  
4. 将cacheBitmap绘制到该View上.  
canvas.drawBitmap(cacheBitmap,0,0,p);

## 3.代码实现 ##

package com.lidong.android_ibrary.view;
    
    import android.content.Context;
    import android.graphics.Bitmap;
    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;
    
    /** *@类名 : DrawView *@描述 : 使用双缓存技术实现绘制 *@时间 : 2016/4/26 9:18 *@作者: 李东 *@邮箱 : lidong@chni.com.cn *@company: chni */
    public class DrawView extends View { 
    
        float preX;
        float preY;
        private Path path;
        private Paint paint = null;
        private int VIEW_WIDTH = 800;
        private int VIEW_HEIGHT = 600;
        //定义一个内存中图片，将他作为缓冲区
        Bitmap cacheBitmap = null;
        //定义缓冲区Cache的Canvas对象
        Canvas cacheCanvas = null;
    
        public DrawView(Context context) {
            this(context,null);
        }
    
        public DrawView(Context context, AttributeSet attrs) {
            super(context, attrs);
            //创建一个与该VIew相同大小的缓冲区
            cacheBitmap = Bitmap.createBitmap(VIEW_WIDTH,VIEW_HEIGHT,Bitmap.Config.ARGB_8888);
            //创建缓冲区Cache的Canvas对象
            cacheCanvas = new Canvas();
            path = new Path();
            //设置cacheCanvas将会绘制到内存的bitmap上
            cacheCanvas.setBitmap(cacheBitmap);
            paint = new Paint();
            paint.setColor(Color.RED);
            paint.setFlags(Paint.DITHER_FLAG);
            paint.setStyle(Paint.Style.STROKE);
            paint.setStrokeWidth(5);
            paint.setAntiAlias(true);
            paint.setDither(true);
        }
    
        @Override
        protected void onDraw(Canvas canvas) {
           Paint p = new Paint();
            //将cacheBitmap绘制到该View
            canvas.drawBitmap(cacheBitmap,0,0,p);
            canvas.drawPath(path,paint);
        }
    
    
        @Override
        public boolean onTouchEvent(MotionEvent event) {
            //获取拖动时间的发生位置
             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:
                    //这是是调用了cacheBitmap的Canvas在绘制
                    cacheCanvas.drawPath(path,paint);
                    path.reset();
                    break;
            }
            invalidate();//在UI线程刷新VIew
            return true;
        }
    }

## 4.实现的效果 ##

![这里写图片描述][20160426093515491]

效果就是这样。

[代码地址][Link 1]

[20160426093515491]: /images/20220724/6391ce8f532f40668835a271f0058b52.png
[Link 1]: https://github.com/lidong1665/AndroidRapidLibrary/tree/master/Android-Rapid-Development-Of-Library/android_library/src/main/java/com/lidong/android_ibrary/view