C# Signature:

[DllImport("gdi32.dll")]
static extern IntPtr CreatePolygonRgn(POINT [] lppt, int cPoints,
   int fnPolyFillMode);

User-Defined Types:

POINT

Notes:

Values for fnPolyFillMode can be 1=Alternate or 2=Winding

Tips & Tricks:

System.Drawing.Point can be used instead POINT.

[DllImport("gdi32.dll")]

static extern IntPtr CreatePolygonRgn(Point[] lppt, int cPoints, int fnPolyFillMode);

Sample Code:

/// <summary>

/// Create a border for custom label control

/// </summary>

/// <returns>

/// if int is returned. Function was successful.

/// if string is returned. Function was failed.

/// </returns>

/// <remarks>Created by Jim Vazquez Castan</remarks>

private string SetBorder()

{

    try
    {
    // First we create polygon
    IntPtr forma = CreatePolygonRgn(edges, edges.Length, 1);
    // then we create area
    int iRes = SetWindowRgn(this.Handle, forma, true);

    return iRes.ToString();
    }
    catch (Exception ex) { return ex.Message; }

}

Alternative Managed API:

Do you know one? Please contribute it!