Creating Venn diagram in C# win Form

Question

I need to create a Venn diagram in win form C#. I have been trying to do it using Graphics.DrawEllipse and FillElipse. But I am not sure how do I fill in the common part.

I want to achieve this,

Here is my code for this,

private void panelControlVennDiagram_Paint(object sender, PaintEventArgs e)
{
  Brush brushLeft = new SolidBrush(Color.Blue);
  Brush brushRight = new SolidBrush(Color.LightPink);
  Brush brushCommon = new SolidBrush(Color.Purple);

  Pen pen = new Pen(brushLeft, 10);

  Rectangle leftVenn = new Rectangle(20, 50,100,100);
  Rectangle rightVenn = new Rectangle(90, 50, 100, 100);
  Rectangle commonVenn = new Rectangle(100, 120, 100, 100);

  Font stringFont = new Font("Times New Roman", 9);

  e.Graphics.DrawString("Left:" + leftValue, stringFont, brushLeft, 10,70);
  e.Graphics.DrawString("Right:" + rightValue, stringFont, brushRight, 90,70);
  e.Graphics.DrawString("Common:" + commonValue,stringFont, brushCommon, 100,70);

  // Fill ellipse on screen.
  e.Graphics.FillEllipse(brushLeft, leftVenn);
  e.Graphics.FillEllipse(brushRight, rightVenn);

  e.Graphics.DrawEllipse(Pens.White, leftVenn);
  e.Graphics.DrawEllipse(Pens.White, rightVenn);

}

I am drawing two ellipses and need to have a different color for the common part. I can not use any library. Please help.

Answer 1

you could use a semi-transparent color so that the color of the overlapping parts is the actual composite color of the two circles

Brush brushLeft = new SolidBrush(Color.FromArgb(50, Color.Blue));
Brush brushRight = new SolidBrush(Color.FromArgb(50, Color.Red));

Answer 2

You could add System.Drawing.Drawing2D; namespace to use GraphicPath . Create a graphic path and get the intersection region.

Try this code: (I have commented DrawString for testing purpose)

private void panelControlVennDiagram_Paint(object sender, PaintEventArgs e)
{
    Rectangle leftVenn = new Rectangle(20, 50, 100, 100);
    Rectangle rightVenn = new Rectangle(90, 50, 100, 100);          
    Region region1 = new Region();

    //Font stringFont = new Font("Times New Roman", 9);
    //e.Graphics.DrawString("Left:" , stringFont, brushLeft, 10, 70);
    //e.Graphics.DrawString("Right:" , stringFont, brushRight, 90, 70);
    //e.Graphics.DrawString("Common:", stringFont, brushCommon, 100, 70);

    // Fill ellipse on screen.
    using(Brush brushLeft = new SolidBrush(Color.Blue))
    {    
        e.Graphics.FillEllipse(brushLeft, leftVenn);
        e.Graphics.DrawEllipse(Pens.White, leftVenn);
    }

    using(Brush brushRight = new SolidBrush(Color.LightPink))
    {
        e.Graphics.FillEllipse(brushRight, rightVenn);        
        e.Graphics.DrawEllipse(Pens.White, rightVenn);
    } 

    using (GraphicsPath circle_path = new GraphicsPath())
    {
        circle_path.AddEllipse(leftVenn);
        region1.Intersect(circle_path);
    }

    using (GraphicsPath circle_path = new GraphicsPath())
    {
        circle_path.AddEllipse(rightVenn);
        region1.Intersect(circle_path);
    }

    using(Brush brushCommon = new SolidBrush(Color.Purple))
    {  
        e.Graphics.FillRegion(brushCommon, region1);
    }

}

Output :