How to detect if mouse has clicked inside of a certain shape in c# on winform app?

Question

Let's say that I have a win form app and I have a picture box called pictureBox1. Then I run the following code:

public System.Drawing.Graphics graphics;
public System.Drawing.Pen blackPen = new System.Drawing.Pen(Color.Black, 2);

public void drawVennDiagram()
{
    graphics = pictureBox1.CreateGraphics();
    graphics.DrawEllipse(blackPen, 0, 0, 100, 100);
    graphics.DrawEllipse(blackPen, 55, 0, 100, 100);
}

If I call drawVennDiagram() , it will draw two circles in pictureBox1 and the circles overlap just enough to look like a venn diagram.

What I am trying to achieve is as follows:

• Run Method A if the mouse clicks anywhere outside of the venn diagram but in the picturebox.

• Run Method B if the mouse clicks only inside of the first circle.

• Run Method C if the mouse clicks inside of both circles.

• Run Method D if the mouse clicks only inside of the second circle.

So far I have written the code below, which essentially tracks where the cursor clicks, but I have no way of figuring out which parameter (a, b, c, d) the cursor location follows.

private void pictureBox1_Click(object sender, EventArgs e)
{
    this.Cursor = new Cursor(Cursor.Current.Handle);
    int xCoordinate = Cursor.Position.X;
    int yCoordinate = Cursor.Position.Y;
}

private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
{
    int xCoordinate = e.X;
    int yCoordinate = e.Y;
}

What is the best way to achieve this?

Answer 1

Yes. Given a circle is positioned with center (x_c,y_c) and radius r, a coordinate (x,y) is within the circle if: (x-x_c)²+(y-y_c)²≤r².

Given we know that, we also know that your circles have a center at (50,50) and (105,50) and each have a radius of 50. So now we define a method:

public static bool InsideCircle (int xc, int yc, int r, int x, int y) {
    int dx = xc-x;
    int dy = yc-y;
    return dx*dx+dy*dy <= r*r;
}

Now you can use:

private void pictureBox1_MouseUp(object sender, MouseEventArgs e) {
    int x = e.X;
    int y = e.Y;
    bool inA = InsideCircle(50,50,50,x,y);
    bool inB = InsideCircle(105,50,50,x,y);
    if(inA && inB) {
        C();
    } else if(inA) {
        B();
    } else if(inB) {
        D();
    } else {
        A();
    }
}

Note however that for now, the two circles you paint do not overlap anyway.