Drawing a triangle with rounded corners

Question

So here's my code to draw a triangle:

Graphics y = CreateGraphics();
Pen yy = new Pen(Color.Red);
pictureBox1.Refresh();

Point x = new Point(Convert.ToInt32(textBox1.Text)*10, Convert.ToInt32(textBox2.Text)*10);
Point xx = new Point(Convert.ToInt32(textBox3.Text)*10, Convert.ToInt32(textBox4.Text)*10);
Point xxx = new Point(Convert.ToInt32(textBox5.Text)*10, Convert.ToInt32(textBox6.Text)*10);

Point[] u = { x, xx, xxx };
y = pictureBox1.CreateGraphics();
y.DrawPolygon(yy, u);

Is there any way to round the corners on this? I read about it on google and it seems there's only a way to round rectangles, but not triangles.

Is there any command to do that for me or I have to do it manually?

Thanks for replies :)

Answer 1

public GraphicsPath DrawRoundedTriangle(RectangleF Rect, PointF point_A, PointF point_B, PointF point_C, float Radius)
    {
        Radius = (Rect.Height / 9f) * (Radius * 0.2f);
        float Diameter = Radius * 2f;
        float arcSize = (float)((Diameter / 2f) * Math.Sqrt(3.0));
        GraphicsPath path = new GraphicsPath();
        float sweep_angle = 120f; //Angle of Arc in the corners
        if (Radius == 0f)
        {
            //Drawing of triangle without a rounded corner
            path.AddLine(point_A, point_B);
            path.AddLine(point_B, point_C);
            path.AddLine(point_C, point_A);
        }
        else
        {
            PointF[] array = new PointF[6];

            array[0] = new PointF(point_A.X + Radius, point_A.Y - arcSize);  //Left Vertex point
            array[1] = new PointF(point_B.X - Radius, point_B.Y + arcSize); //Top Vertex point
            array[2] = new PointF(point_B.X + Radius, point_B.Y + arcSize); //Top Vertex point
            array[3] = new PointF(point_C.X - Radius, point_C.Y - arcSize); //Right Vertex point
            array[4] = new PointF(point_C.X - arcSize, point_C.Y);        //Right Vertex point
            array[5] = new PointF(point_A.X + arcSize, point_C.Y);       //Left Vertex point

            //Path Creation for Drawing
            path.AddArc( (array[5].X - Radius), (array[5].Y - Diameter), Diameter, Diameter, 90f, sweep_angle);                 //Left Vertex
            path.AddLine(array[0], array[1]);                                                                                   //Left Side Line
            path.AddArc(array[1].X, ((array[1].Y - arcSize) + Radius), Diameter, Diameter, 210f, sweep_angle);                  //Top Vertex
            path.AddLine(array[2], array[3]);                                                                                   //Right Side Line
            path.AddArc((array[3].X - arcSize), (array[3].Y - (Diameter - arcSize)), Diameter, Diameter, 330f, sweep_angle);    //Right Vertex
            path.AddLine(array[4], array[5]);                                                                                   //Bottom Line
        }
        path.CloseFigure();
        return path;
    }

Answer 2

I fought with the math for a bit, then I had an idea...overlaid shapes.

      <Canvas >
     <Polyline Margin="-1 0 0 0"
        Fill="{StaticResource Yellow}" 
        Points="3,14.5 17,14.5 10,2 3,14.5" 
        StrokeStartLineCap="Round" StrokeEndLineCap="Round" StrokeLineJoin="Round"
        Stroke="Black" 
        StrokeThickness="4"/>
     <Polyline Margin="-1 0 0 0"
        Fill="{StaticResource Yellow}" 
        Stroke="{StaticResource Yellow}"
        Points="3,14.5 17,14.5 10,2 3,14.5"   
        StrokeStartLineCap="Round" StrokeEndLineCap="Round" StrokeLineJoin="Round"
        StrokeThickness="3"/>
  </Canvas>

Answer 3

It is not possible out of the box.

You can create rounded polygons like this:

• Change each line by making it shorter (on both ends) by your chosen number of pixels, now line AB is line A1B1..
• Create a GraphicsPath which consists of these lines and in between each pair of lines a curve that connects those new endpoints
• To better control the curves it would help to add a point in the middle between the original corners and the connection of the new endpoints

For a Triangle ABC this would mean to

• Create A1, A2, B1, B2, C1, C2
• Then calculate the middle points A3, B3, C3
• and finally adding to a GraphicsPath:
  • Line A1B1, Curve B1B3B2, Line B2C1, Curve C1C3C2, Line C2A2 and Curve A2A3A1.

Here is a piece of code that uses this method:

A GraphicsPaths to be used in the Paint event:

GraphicsPath GP = null;

A test method with a list of points, making up a triangle - (*) we overdraw by two points to make things easier; one could add the final lines and curves by ading a few lines of code instead..

private void TestButton_Click(object sender, EventArgs e)
{
    Point A = new Point(5, 50);
    Point B = new Point(250, 100);
    Point C = new Point(50, 250);

    List<Point> points = new List<Point>();
    points.Add(A);
    points.Add(B);
    points.Add(C);
    points.Add(A);  // *
    points.Add(B);  // *

    GP = roundedPolygon(points.ToArray(), 20);

    panel1.Invalidate();
}

private void panel1_Paint(object sender, PaintEventArgs e)
{
   if (GP == null) return;
   using (Pen pen = new Pen(Brushes.BlueViolet, 3f))
          e.Graphics.DrawPath(pen, GP);
}


GraphicsPath roundedPolygon(Point[] points, int rounding)
{
    GraphicsPath GP = new GraphicsPath();
    List<Line> lines = new List<Line>();
    for (int p = 0; p < points.Length - 1; p++)
        lines.Add( shortenLine(new Line(points[p], points[p+1]), rounding) );
    for (int l = 0; l < lines.Count - 1; l++)
    {
        GP.AddLine(lines[l].P1, lines[l].P2);
        GP.AddCurve(new Point[] { lines[l].P2, 
                                  supPoint(lines[l].P2,points[l+1], lines[l+1].P1), 
                                  lines[l+1].P1 });

    }
    return GP;
}

// a simple structure
struct Line
{
    public Point P1; public Point P2;
    public Line(Point p1, Point p2){P1 = p1; P2 = p2;}
}

// routine to make a line shorter on both ends
Line shortenLine(Line line, int byPixels)
{
    float len = (float)Math.Sqrt(Math.Pow(line.P1.X - line.P2.X, 2)
                               + Math.Pow(line.P1.Y - line.P2.Y, 2));
    float prop = (len - byPixels) / len;
    Point p2 = pointBetween(line.P1, line.P2, prop);
    Point p1 = pointBetween(line.P1, line.P2, 1 - prop);
    return new Line(p1,p2);
}

// with a proportion of 0.5 the point sits in the middle
Point pointBetween(Point p1, Point p2, float prop)
{
    return new Point((int)(p1.X + (p2.X - p1.X) * prop), 
                     (int)(p1.Y + (p2.Y - p1.Y) * prop));
}

// a supporting point, change the second prop (**) to change the rounding shape! 
Point supPoint(Point p1, Point p2, Point p0)
{
    Point p12 = pointBetween(p1, p2, 0.5f);
    return pointBetween(p12, p0, 0.5f);       // **
}

Example:

Answer 4

I think if you adjust your coordinates appropriately and specify a Width for your Pen greater than 1 and set the LineJoin property to Rounded, you should obtain a triangle with rounded corners.