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Android 项目:画图白板APP开发（五）——橡皮擦（全面）

news 2025/9/11 7:01:15

在画图白板应用中，橡皮擦是一个必不可少的功能。它让用户能够修正错误，精确调整他们的创作。本文将详细介绍如何在Android画图白板应用中实现一个高效且用户友好的橡皮擦功能。主要分为以下部分：

橡皮擦：使用透明笔迹覆盖
一键清屏：清空画布所有内容
按笔迹清除：清除选中的笔迹
橡皮擦（修改原本 Path 结构）：需要更改原笔迹，分割成新笔迹
电子笔笔帽擦除：电子笔笔帽当橡皮擦使用

部分功能演示：

橡皮檫演示效果

一、橡皮擦

1. 使用PorterDuff模式

PorterDuffXfermode是Android中处理图形混合的强大工具。对于橡皮擦，我们可以使用PorterDuff.Mode.CLEAR模式，它会将绘制区域的像素完全清除。

2. 代码

//设置橡皮的属性
paint_eraser.setStrokeWidth(50f);
paint_eraser.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));
paint_eraser.setStyle(Paint.Style.STROKE);
paint_eraser.setStrokeCap(Paint.Cap.ROUND);
paint_eraser.setStrokeJoin(Paint.Join.ROUND);
paint_eraser.setAntiAlias(true);
paint_eraser.setDither(true);
paint_eraser.setFilterBitmap(true);
paint_eraser.setStrokeMiter(1.0f);

注意：此操作不会修改原始的笔迹数据层 (StrokeManager)。它只是在视觉上覆盖。

3. 效果图

擦除前：

擦除后：

二、一键清屏

1. 代码

//清空画布
cacheCanvas.drawColor(0,PorterDuff.Mode.CLEAR);
invalidate();

清空作为Canvas绘制目标的那块Bitmap，PorterDuff.Mode.CLEAR: 这是核心所在。它是一种混合模式（Blending Mode），其规则是：清除目标图像中的所有像素，忽略源图像。无论原本画布上有什么，这个模式都会将其变为完全透明。

三、按笔迹擦除

1.思路

画一条曲线，清除相交的可视化笔画（橡皮擦笔画除外），下面配置笔迹擦除橡皮。

//设置笔画删除的属性
paint_eraser_sliding.setStrokeWidth(3f);//3
paint_eraser_sliding.setColor(Color.parseColor("#E94F4F"));//设置为红色
paint_eraser_sliding.setStyle(Paint.Style.STROKE);
paint_eraser_sliding.setStrokeCap(Paint.Cap.ROUND);
paint_eraser_sliding.setStrokeJoin(Paint.Join.ROUND);
paint_eraser_sliding.setAntiAlias(true);
paint_eraser_sliding.setDither(true);
paint_eraser_sliding.setFilterBitmap(true);
paint_eraser_sliding.setStrokeMiter(1.0f);
//设置画出来的为虚线
paint_eraser_sliding.setPathEffect( new DashPathEffect(new float[]{20f,10f,5f,10f},0f));

2. 代码

当手指在屏幕上移动，显示笔迹擦除橡皮的同时，记录最新的点和上一个点，判断是否跟可视化笔画相交。

private void actionMove_Sliding(MotionEvent event){//来判断应该删除哪些线条，利用高光显示float cx = (event.getX(0)+ mStartXs[0]) / 2f;float cy = (event.getY(0) + mStartYs[0]) / 2f;mDottedLine.mXY.add(new DottedLineDates.XAndY(event.getX(0),event.getY(0)));mDottedLine.path.quadTo(mStartXs[0], mStartYs[0], cx, cy);//resetDirtyRect(mDottedLine.mRectF,event.getX(0),event.getY(0));//判断是否相交(虚线只用提供两个点即可) isDelete为true时变成高光isCross(mStartXs[0],mStartYs[0],event.getX(0),event.getY(0));mStartXs[0] = event.getX(0);mStartYs[0] = event.getY(0);paths[0].moveTo(cx, cy);cacheCanvas.drawColor(0,PorterDuff.Mode.CLEAR);  //这个很关键invalidateReason = REASON_DRAW_MOVE;invalidate();
}

可视化笔迹的类型：线和点 ，删除笔迹的标准有所不同

线：判断是否相交
点：判断是否相切

为了更严谨些，线除了判断相交之外；还需要判断起点和终点是否相切。下面的代码我只写了起点的判断，还有另外原因，是因为用电子笔按下的点，很大可能性是经历了多个move点，这些move点是重叠的。判断起点是为了排除类似的点。

//判断每个false的是否相交
private void isCross(float x1, float y1, float x2, float y2) {for (int i = 0; i < mPaintedList.size(); i++) {//假如为橡皮擦就continueif(mPaintedList.get(i).mPaint.getXfermode()==paint_eraser.getXfermode()){//如果为橡皮，就passcontinue;}boolean isEnding = false;while (!mPaintedList.get(i).isDelete()&&!isEnding){//判断DOTTED_LINE是否为点（在压力发生改变的时候他就会运行到move）所以这个点很难捕捉//假如没有准备删除就遍历(有两种类型的处理：点和线)if(mPaintedList.get(i).getLineModel()==LINE||mPaintedList.get(i).getLineModel()==DOTTED_LINE){//目前是对线的处理//System.out.println("AAAAAAAAAAAAAAAA 进入了while循环:线 id "+i);boolean b1; //对首点的判断float pointWidth = pointToLine(x1,y1,x2,y2,mPaintedList.get(i).mXToMatrix,mPaintedList.get(i).mYToMatrix);b1 = pointWidth<=mPaintedList.get(i).mWidth;for (int j = 0; j < mPaintedList.get(i).mOnePaths.size() ; j++) {boolean b ;if(j==0){//使用最开始保存的点b = intersection(x1,y1,x2,y2,mPaintedList.get(i).mXToMatrix,mPaintedList.get(i).mYToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);}else {b = intersection(x1,y1,x2,y2,mPaintedList.get(i).mOnePaths.get(j-1).xToMatrix,mPaintedList.get(i).mOnePaths.get(j-1).yToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);}if(b||b1){//如果判断出相交 == 成为待删除//System.out.println("AAAAAAAAAAAAAAAA 查找到了一条可擦线段  id为："+ i);mPaintedList.get(i).setDelete(true);//同时保存到删除备选
//                            if(mDeleteList == null){
//                                mDeleteList = new ArrayList<>();
//                            }
//                            mDeleteList.add(new PaintDates(mPaintedList.get(i).mPaint,mPaintedList.get(i).mOnePaths
//                                    ,mPaintedList.get(i).mx,mPaintedList.get(i).my,mPaintedList.get(i).mWidth)); //这里的isDelete默认为falsebreak;}//当结束的时候if(j == (mPaintedList.get(i).mOnePaths.size()- 1)){//结束while循环isEnding=true;}}}else {//对点的处理float pointWidth = pointToLine(x1,y1,x2,y2,mPaintedList.get(i).mXToMatrix,mPaintedList.get(i).mYToMatrix);if(pointWidth<=mPaintedList.get(i).mWidth){//System.out.println("AAAAAAAAAAAAAAAA 查找到了一条可擦点点  id为："+ i);mPaintedList.get(i).setDelete(true);//同时保存到删除备选
//                        if(mDeleteList == null){
//                            mDeleteList = new ArrayList<>();
//                        }
//                        mDeleteList.add(new PaintDates(mPaintedList.get(i).mPaint,mPaintedList.get(i).mOnePaths
//                                ,mPaintedList.get(i).mx,mPaintedList.get(i).my,mPaintedList.get(i).mWidth)); //这里的isDelete默认为falsebreak;}//当结束的时候isEnding=true;}}}
}// 点到直线的最短距离的判断 点（x0,y0） 到由两点组成的线段（x1,y1） ,( x2,y2 )
private float pointToLine(float x1, float y1, float x2, float y2, float x0,float y0) {float space = 0;float a, b, c;a = distanceTo(x1, y1, x2, y2);// 线段的长度b = distanceTo(x1, y1, x0, y0);// (x1,y1)到点的距离c = distanceTo(x2, y2, x0, y0);// (x2,y2)到点的距离if (c <= 0.000001 || b <= 0.000001) {space = 0;return space;}if (a <= 0.000001) {space = b;return space;}if (c * c >= a * a + b * b) {space = b;return space;}if (b * b >= a * a + c * c) {space = c;return space;}float p = (a + b + c) / 2;// 半周长float s = (float) Math.sqrt(p * (p - a) * (p - b) * (p - c));// 海伦公式求面积space = 2 * s / a;// 返回点到线的距离（利用三角形面积公式求高）return space;
}//判断两条直线是否相交
public static boolean intersection(double l1x1, double l1y1, double l1x2, double l1y2,double l2x1, double l2y1, double l2x2, double l2y2)
{// 快速排斥实验 首先判断两条线段在 x 以及 y 坐标的投影是否有重合。 有一个为真，则代表两线段必不可交。if (Math.max(l1x1,l1x2) < Math.min(l2x1 ,l2x2)|| Math.max(l1y1,l1y2) < Math.min(l2y1,l2y2)|| Math.max(l2x1,l2x2) < Math.min(l1x1,l1x2)|| Math.max(l2y1,l2y2) < Math.min(l1y1,l1y2)){return false;}// 跨立实验  如果相交则矢量叉积异号或为零，大于零则不相交return !((((l1x1 - l2x1) * (l2y2 - l2y1) - (l1y1 - l2y1) * (l2x2 - l2x1))* ((l1x2 - l2x1) * (l2y2 - l2y1) - (l1y2 - l2y1) * (l2x2 - l2x1))) > 0)&& !((((l2x1 - l1x1) * (l1y2 - l1y1) - (l2y1 - l1y1) * (l1x2 - l1x1))* ((l2x2 - l1x1) * (l1y2 - l1y1) - (l2y2 - l1y1) * (l1x2 - l1x1))) > 0);
}

流程：

遍历所有可视化线段（排除橡皮擦）
遍历过程中，先判断线段起点是否跟传入的线段相切。
接着判断可视化线段每个点组成的线段，是否跟传入的线段相交。
判断相切或相交了，就将其设置为待删除，同时设置该曲线为高光加粗效果。
点的逻辑就只需判断相切即可。

注意：xToMatrix 和 yToMatrix 在这里是偏移和放大缩小后的线段点的位置，这个在后续讲解放大缩小时会讲解，各个功能之间相互配合，让程序更出彩。

当手指松开之后，就执行下面的代码。

private void actionUp_Sliding(){//UP开始的时候就开始删除（可能有多个）//1.查找并删除(依据撤销，没必要删除)for (int i = mPaintedList.size()-1 ; i>=0 ; i--) {//反着删除if(mPaintedList.get(i).isDelete()){if(mCancelList.get(mCancelList.size()-1).MassageType==SLIDING_MULTI_STROKE_UN_HAVE){//设置成有效操作mCancelList.get(mCancelList.size()-1).MassageType=SLIDING_MULTI_STROKE_HAVE;mCancelList.get(mCancelList.size()-1).paintStrokes = new ArrayList<>();}mCancelList.get(mCancelList.size()-1).paintStrokes.add(new MessageStrokes.IdAndStrokes(i,new PaintDates(mPaintedList.get(i))));mPaintedList.remove(i);}}cacheCanvas.drawColor(0,PorterDuff.Mode.CLEAR);
}

这里简单点理解就是将 mPaintedList.get(i) 的笔迹移除到了mCancelList.get(mCancelList.size()-1).paintStrokes 中，这里的mCancelList是撤销恢复使用的，在这里无需理会。

注意：这里反向删除，是为了避免以下问题。

当从一个 List 中正向遍历（从0到size-1）并删除元素时，每删除一个元素，后续元素的索引都会前移（即索引值减1），这会导致：

如果删除第i个元素，那么原本第i+1个元素会变成第i个，但循环索引i会继续增加，从而跳过这个元素。

还可能因为索引越界而引发异常（比如删除后列表大小变化，但循环仍试图访问原索引）。

反向遍历（从size-1到0）删除可以避免这个问题：

删除一个元素后，前面元素的索引不会改变（因为删除的是当前索引i，而i是递减的，下一个要检查的是i-1，不受删除影响）。

这样确保每个元素都被正确遍历，且不会出现索引越界。

3. 效果图

选中后的状态，其中红色虚线为擦除橡皮的轨迹，高光的笔迹就为待删除的笔迹

删除结果如下：

四、橡皮擦（修改原本 Path 结构）

上面的效果，就是根据橡皮擦将原本 Path 分割的结果。

1. 思路

当橡皮擦经过 Path 的时候，除了可以遮挡笔迹之外，还希望将 Path 在遮挡的位置断开，形成新的 Path 。下面代码是橡皮擦在Move的时候执行的部分代码，需要留意的是isCross_eraser。

}else if(mode == ERASER){mEraser.setLayoutParams(new AbsoluteLayout.LayoutParams((int)maxDistance,(int)maxDistance,(int) (event.getX(0)+relativeOffsetX-maxDistance/2), (int) (event.getY(0)+relativeOffsetY-maxDistance/2)));Paints[0].setLineModel(DOTTED_LINE);resetDirtyRect(mRectFs[0],mStartXs[0],mStartYs[0],event.getX(0)+relativeOffsetX,event.getY(0)+relativeOffsetY);float cx = (event.getX(0)+relativeOffsetX+mStartXs[0])/2f;float cy = (event.getY(0)+relativeOffsetY+mStartYs[0])/2f;//用来判断是否相交，如果相交就在的位置断开即可isCross_eraser(mStartXs[0],mStartYs[0],event.getX(0)+relativeOffsetX,event.getY(0)+relativeOffsetY);if(Paints[0].mPath == null){Paints[0].mPath = new Path(paths[0]);}Paints[0].mOnePaths.add(new PaintDates.PathAndWidth(event.getX(0)+relativeOffsetX,event.getY(0)+relativeOffsetY));Paints[0].mPath.quadTo(mStartXs[0],mStartYs[0],cx,cy);mStartXs[0] = event.getX(0)+relativeOffsetX;mStartYs[0] = event.getY(0)+relativeOffsetY;
}

2. 代码

//用来判断是否相交，如果相交就在的位置断开即可
private void isCross_eraser(float x1, float y1, float x2, float y2) {PointF pointF;for (int i = 0; i < mPaintedList.size(); i++) {boolean isEnding = false;while (!isEnding){//判断DOTTED_LINE是否为点（在压力发生改变的时候他就会运行到move）所以这个点很难捕捉//假如没有准备删除就遍历(有两种类型的处理：点和线)if(mPaintedList.get(i).mPaint.getXfermode()==paint_eraser.getXfermode()){//如果为橡皮，就passbreak;}if(mPaintedList.get(i).getLineModel()==POINT){break;}if(mPaintedList.get(i).getLineModel()==LINE||mPaintedList.get(i).getLineModel()==DOTTED_LINE){//目前是对线的处理(除开对橡皮的处理)//其实可以两个点之间就设置一个点（并且实时更新就可）for (int j = 0; j < mPaintedList.get(i).mOnePaths.size() ; j++) {boolean b ;if(j==0){b = intersection(x1,y1,x2,y2,mPaintedList.get(i).mXToMatrix,mPaintedList.get(i).mYToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);}else {b = intersection(x1,y1,x2,y2,mPaintedList.get(i).mOnePaths.get(j-1).xToMatrix,mPaintedList.get(i).mOnePaths.get(j-1).yToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);}if(b){//如果判断出相交 == 成为待删除//System.out.println("AAAAAAAAAAAAAAAA 查找到了一条可擦线段  id为："+ i);//mPaintedList.get(i).setDelete(true);//设置状态，求比例，保存在两点之间（因为有漫游效果，所以求点是不现实的）//遍历一笔，看到底有几个交点：决定分成多少段if(!mPaintedList.get(i).isCut()){mPaintedList.get(i).setCut(true);}mPaintedList.get(i).mOnePaths.get(j).isCut = true;if(j==0){pointF = intersectionXY(x1,y1,x2,y2,mPaintedList.get(i).mXToMatrix,mPaintedList.get(i).mYToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);//assert pointF != null;  //他为空了，中断程序if(pointF!=null){mPaintedList.get(i).mOnePaths.get(j).BL = distanceTo(mPaintedList.get(i).mXToMatrix,mPaintedList.get(i).mYToMatrix,pointF.x,pointF.y)/distanceTo(mPaintedList.get(i).mXToMatrix,mPaintedList.get(i).mYToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);}else {mPaintedList.get(i).mOnePaths.get(j).isCut = false; //没有值就设置为不割}}else {pointF = intersectionXY(x1,y1,x2,y2,mPaintedList.get(i).mOnePaths.get(j-1).xToMatrix,mPaintedList.get(i).mOnePaths.get(j-1).yToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);//assert pointF != null;if(pointF!=null){mPaintedList.get(i).mOnePaths.get(j).BL = distanceTo(mPaintedList.get(i).mOnePaths.get(j-1).xToMatrix,mPaintedList.get(i).mOnePaths.get(j-1).yToMatrix,pointF.x,pointF.y)/distanceTo(mPaintedList.get(i).mOnePaths.get(j-1).xToMatrix,mPaintedList.get(i).mOnePaths.get(j-1).yToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);}else {mPaintedList.get(i).mOnePaths.get(j).isCut = false; //没有值就设置为不割}//System.out.println("AAAAAAAAAAAAAAAAAAAAAAAA"+pointF.x+","+pointF.y+",j="+j+",bl="+mPaintedList.get(i).mOnePaths.get(j).BL);}}if(j == (mPaintedList.get(i).mOnePaths.size()- 1)){//结束while循环（必须遍历所有，知道结尾）isEnding=true;}}}}}
}//判断交点
public static PointF intersectionXY(float x1, float y1, float x2, float y2,float x3, float y3, float x4, float y4)
{float x;float y;float k1=Float.MAX_VALUE;float k2=Float.MAX_VALUE;boolean flag1=false;boolean flag2=false;if((x1-x2)==0)flag1=true;if((x3-x4)==0)flag2=true;if(!flag1)k1=(y1-y2)/(x1-x2);if(!flag2)k2=(y3-y4)/(x3-x4);if(flag1){x=x1;if(k2==0){y=y3;}else{y=k2*(x-x4)+y4;}}else if(flag2){x=x3;if(k1==0){y=y1;}else{y=k1*(x-x2)+y2;}}else{if(k1==0){y=y1;x=(y-y4)/k2+x4;}else if(k2==0){y=y3;x=(y-y2)/k1+x2;}else{x=(k1*x2-k2*x4+y4-y2)/(k1-k2);y=k1*(x-x2)+y2;}}if(between(x1,x2,x)&&between(y1,y2,y)&&between(x3,x4,x)&&between(y3,y4,y)){PointF point=new PointF();point.x = x;point.y = y;return point;}return null;
}

逻辑：

流程跟按笔迹擦除差不多，判断相交之后，保存交点和区域段（需要切割的区域）
move的时候，只需要记录数据。等到手指松开执行 up 时，再去切割所有线段

接下来是松手后执行的代码

private void actionUp_Eraser(){mEraser.setVisibility(GONE);int size =mPaintedList.size();//这里将其分段（理论上分段的操作应该是不会显示出不同的）for (int i = 0 ; i< size ; i++)for (int i = 0 ; i< size ; i++){if(mPaintedList.get(i).isCut()){ //当此线是准备是剪切的//这里是不透明笔锋if(mPaintedList.get(i).getLineModel()==LINE){mCutList.add(new PaintDatesAndID());//首先要添加一个笔画mCutList.get(mCutList.size()-1).id = i;mCutList.get(mCutList.size()-1).mCutPaintList.add(new PaintDates(mPaintedList.get(i).mPaint,new ArrayList<>(),mPaintedList.get(i).mx,mPaintedList.get(i).my,mPaintedList.get(i).mWidth));mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mXToMatrix = mPaintedList.get(i).mXToMatrix;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mYToMatrix = mPaintedList.get(i).mYToMatrix;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).setLineModel(mPaintedList.get(i).getLineModel());mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath = mPaintedList.get(i).mPath;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mMatrixS.addAll(mPaintedList.get(i).mMatrixS) ; //这里存疑for (int j = 0; j <mPaintedList.get(i).mOnePaths.size() ; j++) {float cx;float cy;if(mPaintedList.get(i).mOnePaths.get(j).isCut){//根据比例求点PointF pointF ;PointF pointF1; //偏移点if(j==0){pointF= pointToBL(mPaintedList.get(i).mOnePaths.get(j).BL,mPaintedList.get(i).mx, mPaintedList.get(i).my,mPaintedList.get(i).mOnePaths.get(j).x, mPaintedList.get(i).mOnePaths.get(j).y);pointF1= pointToBL(mPaintedList.get(i).mOnePaths.get(j).BL,mPaintedList.get(i).mXToMatrix, mPaintedList.get(i).mYToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);}else {pointF= pointToBL(mPaintedList.get(i).mOnePaths.get(j).BL,mPaintedList.get(i).mOnePaths.get(j-1).x, mPaintedList.get(i).mOnePaths.get(j-1).y,mPaintedList.get(i).mOnePaths.get(j).x, mPaintedList.get(i).mOnePaths.get(j).y);pointF1= pointToBL(mPaintedList.get(i).mOnePaths.get(j).BL,mPaintedList.get(i).mOnePaths.get(j-1).xToMatrix, mPaintedList.get(i).mOnePaths.get(j-1).yToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);}mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.add(new PaintDates.PathAndWidth(new Path(mPaintedList.get(i).mOnePaths.get(j).path), mPaintedList.get(i).mOnePaths.get(j).width, pointF.x, pointF.y));mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).xToMatrix = pointF1.x;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).yToMatrix = pointF1.y;if(j==0){mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).path.moveTo( mPaintedList.get(i).mx, mPaintedList.get(i).my);cx = (mPaintedList.get(i).mx+ pointF.x)/2f;cy = (mPaintedList.get(i).my+ pointF.y)/2f;}else {mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).path.moveTo( mPaintedList.get(i).mOnePaths.get(j-1).x, mPaintedList.get(i).mOnePaths.get(j-1).y);cx = (mPaintedList.get(i).mOnePaths.get(j-1).x+ pointF.x)/2f;cy = (mPaintedList.get(i).mOnePaths.get(j-1).y+ pointF.y)/2f;}mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).path.lineTo(cx, cy);//new下一个mCutList.get(mCutList.size()-1).mCutPaintList.add(new PaintDates(mPaintedList.get(i).mPaint,new ArrayList<>(),pointF.x,pointF.y,mPaintedList.get(i).mWidth));mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mXToMatrix = pointF1.x;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mYToMatrix = pointF1.y;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).setLineModel(mPaintedList.get(i).getLineModel());mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath = mPaintedList.get(i).mPath;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mMatrixS.addAll(mPaintedList.get(i).mMatrixS); //这里存疑mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.add(new PaintDates.PathAndWidth(new Path(mPaintedList.get(i).mOnePaths.get(j).path), mPaintedList.get(i).mOnePaths.get(j).width,  mPaintedList.get(i).mOnePaths.get(j).x, mPaintedList.get(i).mOnePaths.get(j).y));mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).path.reset();mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).path.moveTo( pointF.x, pointF.y);mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).path.lineTo(mPaintedList.get(i).mOnePaths.get(j).x, mPaintedList.get(i).mOnePaths.get(j).y);mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).xToMatrix = mPaintedList.get(i).mOnePaths.get(j).xToMatrix;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).yToMatrix = mPaintedList.get(i).mOnePaths.get(j).yToMatrix;}else {mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.add(new PaintDates.PathAndWidth(new Path(mPaintedList.get(i).mOnePaths.get(j).path), mPaintedList.get(i).mOnePaths.get(j).width, mPaintedList.get(i).mOnePaths.get(j).x, mPaintedList.get(i).mOnePaths.get(j).y));if(mPaintedList.get(i).mOnePaths.get(j).addPaths!=null){mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).addPaths = new ArrayList<>(mPaintedList.get(i).mOnePaths.get(j).addPaths) ;}mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).xToMatrix = mPaintedList.get(i).mOnePaths.get(j).xToMatrix;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).yToMatrix = mPaintedList.get(i).mOnePaths.get(j).yToMatrix;}}}else {//这里是透明笔画（用path的）mCutList.add(new PaintDatesAndID());//首先要添加一个笔画mCutList.get(mCutList.size()-1).mCutPaintList.add(new PaintDates(mPaintedList.get(i).mPaint,new ArrayList<>(),mPaintedList.get(i).mx,mPaintedList.get(i).my,mPaintedList.get(i).mWidth));mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mXToMatrix = mPaintedList.get(i).mXToMatrix;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mYToMatrix = mPaintedList.get(i).mYToMatrix;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).setLineModel(mPaintedList.get(i).getLineModel());mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath = new Path();mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath.moveTo(mPaintedList.get(i).mx,mPaintedList.get(i).my);mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mMatrixS.addAll(mPaintedList.get(i).mMatrixS) ; //这里存疑for (int j = 0; j <mPaintedList.get(i).mOnePaths.size() ; j++){float cx;float cy;if(mPaintedList.get(i).mOnePaths.get(j).isCut){PointF pointF ;PointF pointF1; //偏移点if(j==0){pointF= pointToBL(mPaintedList.get(i).mOnePaths.get(j).BL,mPaintedList.get(i).mx, mPaintedList.get(i).my,mPaintedList.get(i).mOnePaths.get(j).x, mPaintedList.get(i).mOnePaths.get(j).y);pointF1= pointToBL(mPaintedList.get(i).mOnePaths.get(j).BL,mPaintedList.get(i).mXToMatrix, mPaintedList.get(i).mYToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);cx = (mPaintedList.get(i).mx+pointF.x)/2f;cy = (mPaintedList.get(i).my+pointF.y)/2f;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath.quadTo(mPaintedList.get(i).mx,mPaintedList.get(i).my,cx,cy);}else {pointF= pointToBL(mPaintedList.get(i).mOnePaths.get(j).BL,mPaintedList.get(i).mOnePaths.get(j-1).x, mPaintedList.get(i).mOnePaths.get(j-1).y,mPaintedList.get(i).mOnePaths.get(j).x, mPaintedList.get(i).mOnePaths.get(j).y);pointF1= pointToBL(mPaintedList.get(i).mOnePaths.get(j).BL,mPaintedList.get(i).mOnePaths.get(j-1).xToMatrix, mPaintedList.get(i).mOnePaths.get(j-1).yToMatrix,mPaintedList.get(i).mOnePaths.get(j).xToMatrix, mPaintedList.get(i).mOnePaths.get(j).yToMatrix);cx = (mPaintedList.get(i).mOnePaths.get(j-1).x+pointF.x)/2f;cy = (mPaintedList.get(i).mOnePaths.get(j-1).y+pointF.y)/2f;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath.quadTo(mPaintedList.get(i).mOnePaths.get(j-1).x,mPaintedList.get(i).mOnePaths.get(j-1).y,cx,cy);}mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.add(new PaintDates.PathAndWidth(pointF.x, pointF.y));mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).xToMatrix = pointF1.x;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).yToMatrix = pointF1.y;//该new一个了mCutList.get(mCutList.size()-1).mCutPaintList.add(new PaintDates(mPaintedList.get(i).mPaint,new ArrayList<>(),pointF.x, pointF.y,mPaintedList.get(i).mWidth));mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mXToMatrix =  pointF1.x;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mYToMatrix =  pointF1.y;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).setLineModel(mPaintedList.get(i).getLineModel());mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath = new Path();mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath.moveTo(pointF.x, pointF.y);mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mMatrixS.addAll(mPaintedList.get(i).mMatrixS) ; //这里存疑cx = (pointF.x+mPaintedList.get(i).mOnePaths.get(j).x)/2f;cy = (pointF.y+mPaintedList.get(i).mOnePaths.get(j).y)/2f;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath.quadTo(pointF.x,pointF.y,cx,cy);mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.add(new PaintDates.PathAndWidth(mPaintedList.get(i).mOnePaths.get(j).x, mPaintedList.get(i).mOnePaths.get(j).y));mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).xToMatrix = mPaintedList.get(i).mOnePaths.get(j).xToMatrix;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).yToMatrix = mPaintedList.get(i).mOnePaths.get(j).yToMatrix;}else {if(j==0){cx = (mPaintedList.get(i).mx+mPaintedList.get(i).mOnePaths.get(j).x)/2f;cy = (mPaintedList.get(i).my+mPaintedList.get(i).mOnePaths.get(j).y)/2f;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath.quadTo(mPaintedList.get(i).mx,mPaintedList.get(i).my,cx,cy);}else {cx = (mPaintedList.get(i).mOnePaths.get(j-1).x+mPaintedList.get(i).mOnePaths.get(j).x)/2f;cy = (mPaintedList.get(i).mOnePaths.get(j-1).y+mPaintedList.get(i).mOnePaths.get(j).y)/2f;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mPath.quadTo(mPaintedList.get(i).mOnePaths.get(j-1).x,mPaintedList.get(i).mOnePaths.get(j-1).y,cx,cy);}mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.add(new PaintDates.PathAndWidth(mPaintedList.get(i).mOnePaths.get(j).x, mPaintedList.get(i).mOnePaths.get(j).y));mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).xToMatrix = mPaintedList.get(i).mOnePaths.get(j).xToMatrix;mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.get(mCutList.get(mCutList.size()-1).mCutPaintList.get(mCutList.get(mCutList.size()-1).mCutPaintList.size()-1).mOnePaths.size()-1).yToMatrix = mPaintedList.get(i).mOnePaths.get(j).yToMatrix;}}}//在这里保存数字//mNumList.add(mCutList.size());}}if(mCutList.size()!=0){for (int i = mCutList.size()-1; i >= 0; i--) {//从最后一个分割的开始添加，此时包括之前的线+分割线mPaintedList.addAll(mCutList.get(i).id,mCutList.get(i).mCutPaintList);for (int j = 0; j < mCutList.get(i).mCutPaintList.size() ; j++) {mCancelList.get(mCancelList.size()-1).paintStrokes.add(new MessageStrokes.IdAndStrokes(mCutList.get(i).id,null));//一定要倒着来}}mCutList.clear();}//将他们delete  +mCutList.size()for (int j = mPaintedList.size()-1; j>=0 ; j--) {if(mPaintedList.get(j).isCut()){mCancelList.get(mCancelList.size()-1).paintStrokes.add(new MessageStrokes.IdAndStrokes(j,new PaintDates(mPaintedList.get(j))));mPaintedList.remove(j);}}if(Paints[0]!=null){mPaintedList.add(new PaintDates(Paints[0].mPaint,Paints[0].mOnePaths,Paints[0].mx,Paints[0].my,Paints[0].mWidth));mPaintedList.get(mPaintedList.size()-1).setLineModel(Paints[0].getLineModel());mPaintedList.get(mPaintedList.size()-1).mPath = Paints[0].mPath;mPaintedList.get(mPaintedList.size() - 1).draw(cacheCanvas);}paths[0].reset();Paints[0] = null;
}

代码有点多，我简单说说流程：整体分为四个阶

阶段一：遍历并处理被切割的笔画

核心逻辑：正向遍历所有笔画，找到被标记为“切割”（isCut()）的笔画进行处理。

处理分为两种模式：

1. 不透明笔锋模式 (LINE)

创建新的切割记录：在mCutList中添加一个PaintDatesAndID对象。

复制原笔画属性：创建一个新的PaintDates对象，复制原笔画的 paint、坐标、宽度等基本属性。

遍历笔画的每个线段 (mOnePaths)：

如果线段被切割 (isCut):

计算切割点坐标（pointF）和对应的矩阵变换点（pointF1）。

将当前线段在切割点处分割：

当前子笔画结束于切割点。

创建一个新的子笔画从切割点开始。

如果线段未被切割:

直接将整个线段添加到当前子笔画中。

2. 透明笔画模式（非LINE，使用Path）

逻辑与不透明模式类似，但使用Path和二次贝塞尔曲线（quadTo）来构建平滑的笔迹。

同样在切割点处分割Path，并创建新的子笔画。

阶段二：将分割后的笔画重新插入原列表

反向遍历mCutList（从最后处理的笔画开始）。

将分割后产生的子笔画列表（mCutPaintList）插入回原笔画列表（mPaintedList）的原始位置（mCutList.get(i).id）。

为撤销功能记录这些操作（添加到mCancelList）。

清空临时切割列表mCutList。

阶段三：清理被标记为切割的原始笔画

反向遍历当前所有笔画。

找到所有仍被标记为“切割”的原始笔画（这些是刚刚被分割处理的原始笔画）。

将它们从mPaintedList中移除，并添加到撤销列表中。

阶段四：处理当前正在绘制的笔画

如果存在正在绘制的笔画（Paints[0]），将其完成并添加到笔画列表中。

绘制到缓存画布上。

重置路径和笔画变量，为下一次绘制做准备。

五、电子笔笔帽擦除

通过判断是否为MotionEvent.TOOL_TYPE_ERASER，不同的的厂商电子笔的数据有所不同，但是使用方式大差不差。当识别到时，更改为上面的介绍的几种橡皮擦即可。

int toolType = event.getToolType(0);
if(toolType == MotionEvent.TOOL_TYPE_ERASER){
//实现逻辑
}

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1. 使用PorterDuff模式

2. 代码

3. 效果图

二、一键清屏

1. 代码

三、按笔迹擦除

1.思路

2. 代码

3. 效果图

四、橡皮擦（修改原本 Path 结构）

1. 思路

2. 代码

阶段一：遍历并处理被切割的笔画

1. 不透明笔锋模式 (`LINE`)

2. 透明笔画模式（非`LINE`，使用Path）

阶段二：将分割后的笔画重新插入原列表

阶段三：清理被标记为切割的原始笔画

阶段四：处理当前正在绘制的笔画

五、电子笔笔帽擦除

相关文章：

一、橡皮擦

1. 使用PorterDuff模式

2. 代码

3. 效果图

二、一键清屏

1. 代码

三、按笔迹擦除

1.思路

2. 代码

3. 效果图

四、橡皮擦（修改原本 Path 结构）

1. 思路

2. 代码

阶段一：遍历并处理被切割的笔画

1. 不透明笔锋模式 (LINE)

2. 透明笔画模式（非LINE，使用Path）

阶段二：将分割后的笔画重新插入原列表

阶段三：清理被标记为切割的原始笔画

阶段四：处理当前正在绘制的笔画

五、电子笔笔帽擦除

相关文章：

1. 不透明笔锋模式 (`LINE`)

2. 透明笔画模式（非`LINE`，使用Path）