单击一个形状WinForm

Question

I am drawing a circle of _radius = 50 pixels in the center of the form:

g.FillEllipse(Brushes.Red, this.ClientRectangle.Width / 2 - _radius / 2, this.ClientRectangle.Height / 2 - _radius / 2, _radius, _radius);

Now I want to check if the user clicked in the form.

if (e.Button == MouseButtons.Left)
{
    int w = this.ClientRectangle.Width;
    int h = this.ClientRectangle.Height;

    double distance = Math.Sqrt((w/2 - e.Location.X) ^ 2 + (h/2 - e.Location.Y) ^ 2);
    ....

 if (distance <_radius)
    return true;
 else
    return false;
}

Now I am ending up with wrong values. For instance if I click on the edge of the circle I at times get distance of ~10 or NaN at times. What am I doing wrong here?

Answer 1

1. You're performing integer division, which is coarser than floating-point division.
2. ^ is not the "power-to" operator, it's the bitwise XOR operator , which is probably not what you want. Use Math.Pow or x*x instead.
3. You can simplify the last statement by simply doing return distance < _radius .

Try this:

Single w = this.ClientRectangle.Width;
Single h = this.ClientRectangle.Height;

Single distanceX = w / 2f - e.Location.X;
Single distanceY = h / 2f - e.Location.Y;

Single distance = Math.Sqrt( distanceX  * distanceX + distanceY * distanceY );

return distance < this._radius;

(This code does not change any assumptions about the location of the circle).