从圆圈android

Question

我可以编写一个应用程序来绘制，但我有一个问题

我想从圆圈开始绘画， 我的出发点始终是圆圈，我怎么能这样做？

现在我可以从任何一点画画，我试图找到屏幕的中间但是它不起作用

    public CanvasView(Context context, AttributeSet attrs) {
    super(context, attrs);
    this.context = context;
    path = new Path();
    paint = new Paint();
    paint.setColor(Color.RED);
    paint.setAntiAlias(true);
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeJoin(Paint.Join.ROUND);
    paint.setStrokeWidth(20f);
}

@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    mbitmap = Bitmap.createBitmap(w,h,Bitmap.Config.ARGB_8888);
    mcanvas = new Canvas(mbitmap);
}

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    DisplayMetrics metrics = Resources.getSystem().getDisplayMetrics();
    int a = metrics.widthPixels; // to get width of the screen
    int b = metrics.heightPixels;

    canvas.drawCircle(a/2,((b/2)-160),50, paint);
    if ((canDraw)) {
        canvas.drawPath(path, paint);
    }
}

private void startTouch (float x , float y){
    if ((canDraw)) {
    path.moveTo(x,y);
    mX = x;
    mY = y ;
}}
public void moveTouche (float x,float y ) {
    if ((canDraw)) {
    float dx = Math.abs(x - mX);
    float dy = Math.abs(y - mY);
    if(dx >= Tolerance || dy >= Tolerance){
        path.quadTo(mX,mY,(x+mX)/2,(y+mY)/2);
        mX = x ;
        mY = y;

    }}
}
private void upTouch(){
    if ((canDraw)) {
    path.lineTo(mX,mY);
}}

@Override
public boolean onTouchEvent(MotionEvent event) {
    float x = event.getX();
    float y = event.getY();
   switch (event.getAction()){
        case MotionEvent.ACTION_DOWN:
            startTouch(x,y);
            invalidate();
            break ;
        case MotionEvent.ACTION_UP:
            upTouch();
            invalidate();
            break ;
        case MotionEvent.ACTION_MOVE:
            moveTouche(x,y);
            invalidate();
            break;
    }
   return true ;
}
}    

Answer 1

• 找到界定触摸必须从哪个中心区域开始的坐标，或者创建一个标识它的元素

• 在ouTouchEvent内，写下：

  case MotionEvent.ACTION_DOWN:
      if (touchIsInsideCircle(x,y)) {
         startTouch(x,y);
         invalidate();
      }
      break ;
  

• 使用预定义的坐标定义一个知道屏幕中心的函数：

   boolean touchIsInsideCircle(float x, float y) {
       return (x < maxX && x > minX && y < maxY && y > minY);
   }