Android触摸事件实现笔触画布

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

//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Bitmap
Bitmap 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);

 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;
        });
    }

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;
});

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/ms
            double 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;
});

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

//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Canvas
mCanvas = 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ImageView
mIdIvShow.setImageBitmap(mNewBitmap);