How to draw an arrow with DrawLine command

DrawLine in C# (e.g., in WinForms or GDI+) only draws a straight line — it does not support arrows directly. Graphics libraries usually do not support DrawArrow command by default beacuse it is a simple task to mimic DrawArrow command using three DrawLine commands. To draw an arrow, you combine:

• Graphics.DrawLine
• Pen.CustomEndCap (recommended), or
• manual triangle drawing

1. Easiest way: Use CustomEndCap (recommended)

This is the cleanest solution.

using System.Drawing;
using System.Drawing.Drawing2D;

void DrawArrow(Graphics g)
{
    Pen pen = new Pen(Color.Black, 2);

    // Create arrow shape at the end of the line
    AdjustableArrowCap arrowCap = new AdjustableArrowCap(4, 6);
    pen.CustomEndCap = arrowCap;

    g.DrawLine(pen, 50, 50, 200, 50);
}

What happens

• Line is drawn from (50,50) to (200,50)
• Arrowhead is automatically added at the end

2. Alternative: Use LineCap (simpler, less control)

using System.Drawing;
using System.Drawing.Drawing2D;

void DrawArrow(Graphics g)
{
    Pen pen = new Pen(Color.Black, 2);

    pen.EndCap = LineCap.ArrowAnchor;

    g.DrawLine(pen, 50, 80, 200, 80);
}

Notes

• Very simple
• Less customizable than CustomEndCap

3. Manual arrow (for full control)

If you want full control over shape/angle:

void DrawArrow(Graphics g)
{
    Point start = new Point(50, 120);
    Point end = new Point(200, 120);

    // Draw main line
    g.DrawLine(Pens.Black, start, end);

    // Draw arrowhead manually
    float arrowSize = 10;

    var angle = Math.Atan2(end.Y - start.Y, end.X - start.X);

    PointF p1 = new PointF(
        end.X - (float)(arrowSize * Math.Cos(angle - Math.PI / 6)),
        end.Y - (float)(arrowSize * Math.Sin(angle - Math.PI / 6))
    );

    PointF p2 = new PointF(
        end.X - (float)(arrowSize * Math.Cos(angle + Math.PI / 6)),
        end.Y - (float)(arrowSize * Math.Sin(angle + Math.PI / 6))
    );

    g.DrawLine(Pens.Black, end, p1);
    g.DrawLine(Pens.Black, end, p2);
}

Another implementation of DrawArrow

The following method draws an arrow using three DrawLine calls in C# programming language. 

void DrawArrow(double x1, double y1, double x2, double y2, int arrLength = 10)
{
    var m = x2 - x1 == 0 ? 0 : (y2 - y1) / (x2 - x1);
    var degree = Math.Atan(m);

    var toLeft = x2 > x1 ? 0 : Math.PI;

    var degree1 = degree + 5 * Math.PI / 6 + toLeft;
    var degree2 = degree + 7 * Math.PI / 6 + toLeft;

    var px1 = x2 + Math.Cos(degree1) * arrLength;
    var py1 = y2 + Math.Sin(degree1) * arrLength;

    var px2 = x2 + Math.Cos(degree2) * arrLength;
    var py2 = y2 + Math.Sin(degree2) * arrLength;

    var pen = new Pen(Color.Black);
   
    g.DrawLine(pen, x1, y1, x2, y2);
    g.DrawLine(pen, x2, y2, px1, py1);
    g.DrawLine(pen, x2, y2, px2, py2);
}