300字范文 > Android触摸事件实现笔触画布

Android触摸事件实现笔触画布

时间：2022-11-12 14:30:15

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Android触摸事件实现笔触画布

任何View都有触摸事件,经常在自定义控件时重写setOnTouchListener
本篇通过手绘图片来讲述这个知识点

本篇分为三个等级：一览图：

LEVEL1:基础实现

在Activity中通过一个全屏的Bitmap创建的Canvas绘制
为ImageView添加触摸事件监听。

1.成员变量

ImageView mIdIvShow;float downX = 0;float downY = 0;float upX = 0;float upY = 0;private Canvas mCanvas;private Paint mPaint;

2.创建画布

//获取屏幕尺寸Point point = new Point();getWindowManager().getDefaultDisplay().getSize(point);//创建一个和屏幕一样大的BitmapBitmap bitmap = Bitmap.createBitmap(point.x, point.y, Bitmap.Config.ARGB_8888);//创建Canvas对象mCanvas = new Canvas(bitmap);mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);mPaint.setStrokeWidth(10);mPaint.setColor(Color.RED);//将bitmap用ImageView展示mIdIvShow.setImageBitmap(bitmap);

3.监听事件

mIdIvShow.setOnTouchListener((v, event) -> {switch (event.getAction()) {case MotionEvent.ACTION_DOWN:downX = event.getX();downY = event.getY();L.d("按下:(" + downX + "," + downY + ")" + L.l());break;case MotionEvent.ACTION_CANCEL:break;case MotionEvent.ACTION_MOVE:break;case MotionEvent.ACTION_UP:upX = event.getX();upY = event.getY();L.d("抬起:(" + upX + "," + upY + ")" + L.l());mCanvas.drawLine(downX, downY, upX, upY, mPaint);mIdIvShow.invalidate();//更新视图break;}return true;});}

升级版：LEVER2

LEVEL2.png

mIdIvShow.setOnTouchListener((v, event) -> {switch (event.getAction()) {case MotionEvent.ACTION_DOWN:downX = event.getX();downY = event.getY();break;case MotionEvent.ACTION_CANCEL:break;case MotionEvent.ACTION_MOVE:upX = event.getX();upY = event.getY();mCanvas.drawLine(downX, downY, upX, upY, mPaint);mIdIvShow.invalidate();//更新点位downY = upY;downX = upX;break;case MotionEvent.ACTION_UP://抬起点Y>1100,清除笔迹if (upY > 1100) {Paint paint = new Paint();paint.setColor(Color.WHITE);mCanvas.drawRect(0, 0, mPoint.x, mPoint.y, paint);}break;}return true;});

再升级版：LEVER3

笔触根据绘制的速度动态改变画笔粗细

LEVER3.png

float movingX = 0;float movingY = 0;private long lastTimestamp = 0L;//最后一次的时间戳

mIdIvShow.setOnTouchListener((view, event) -> {switch (event.getAction()) {case MotionEvent.ACTION_DOWN:lastTimestamp = System.currentTimeMillis();downX = event.getX();downY = event.getY();break;case MotionEvent.ACTION_CANCEL:break;case MotionEvent.ACTION_MOVE:movingX = event.getX();movingY = event.getY();long curTimestamp = System.currentTimeMillis();//计算时间差long detaT = curTimestamp - lastTimestamp;//计算距离差float detaS = Logic.disPos2d(movingX, movingY, downX, downY);//由于速度是 px/msdouble v = detaS / detaT;//速度转化为画笔宽度的等式float width = 14/(float)v;L.d(width + L.l());//限制极值情况if ((width > 0) && width < 30) {mPaint.setStrokeWidth(width);}mCanvas.drawLine(downX, downY, movingX, movingY, mPaint);mIdIvShow.invalidate();downX = movingX;downY = movingY;lastTimestamp = curTimestamp;//更新时间movePos.add(new PointF(event.getX(), event.getY()));break;}return true;});

拓展

1.其中可以改变求宽度的等式实现不同的笔触:如

float width = (float) Math.log10(v) * 40;

LEVER3+.png

2.在图片上绘画

//图片原型Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.iv_500x400);//图片副本Bitmap mNewBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), bitmap.getConfig());//用副本生成CanvasmCanvas = new Canvas(mNewBitmap);mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);mPaint.setStrokeCap(Paint.Cap.ROUND);//直线圆头mCanvas.drawBitmap(bitmap, new Matrix(), mPaint);mPaint.setStrokeWidth(10);mPaint.setColor(Color.parseColor("#88164BE6"));//设置副本图片到ImageViewmIdIvShow.setImageBitmap(mNewBitmap);

拓展2.png