Cool, Semi-transparent and Shaped Dialogs with Standard Controls for Windows 2000 and Above

using System;
using System.Drawing;
using System.Runtime.InteropServices;

namespace ImgDlgSample
{
    public enum MousePositionCodes : int
    {
        HTERROR = -2,
        HTTRANSPARENT = -1,
        HTNOWHERE = 0,
        HTCLIENT = 1,
        HTCAPTION = 2,
        HTSYSMENU = 3,
        HTGROWBOX = 4,
        HTSIZE = HTGROWBOX,
        HTMENU = 5,
        HTHSCROLL = 6,
        HTVSCROLL = 7,
        HTMINBUTTON = 8,
        HTMAXBUTTON = 9,
        HTLEFT = 10,
        HTRIGHT = 11,
        HTTOP = 12,
        HTTOPLEFT = 13,
        HTTOPRIGHT = 14,
        HTBOTTOM = 15,
        HTBOTTOMLEFT = 16,
        HTBOTTOMRIGHT = 17,
        HTBORDER = 18,
        HTOBJECT = 19,
        HTCLOSE = 20,
        HTHELP = 21,
    }

    public static class BlendOp
    {
        public const byte AC_SRC_OVER = 0x00;
        public const byte AC_SRC_ALPHA = 0x01;
    }
    

    /// <summary>
    /// BLENDFUNCTION
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct BLENDFUNCTION
    {
        byte BlendOp;
        byte BlendFlags;
        byte SourceConstantAlpha;
        byte AlphaFormat;

        public BLENDFUNCTION(byte op, byte flags, byte alpha, byte format)
        {
            BlendOp = op;
            BlendFlags = flags;
            SourceConstantAlpha = alpha;
            AlphaFormat = format;
        }
    }

    /// <summary>
    /// POINT
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct POINT
    {
        public int X;
        public int Y;

        public POINT(int x, int y)
        {
            this.X = x;
            this.Y = y;
        }

        public static implicit operator Point(POINT p)
        {
            return new Point(p.X, p.Y);
        }

        public static implicit operator POINT(Point p)
        {
            return new POINT(p.X, p.Y);
        }
    }


    /// <summary>
    /// SIZE
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct SIZE
    {
        public int cx;
        public int cy;

        public SIZE(int cx, int cy)
        {
            this.cx = cx;
            this.cy = cy;
        }
    } 

    public static class CompressionType
    {
        public const byte BI_RGB = 0;
        public const byte BI_RLE8 = 1;
        public const byte BI_RLE4 = 2;
        public const byte BI_BITFIELDS = 3;
        public const byte BI_JPEG = 4;
        public const byte BI_PNG = 5;
    }

    public static class DIBColorTableIdentifier
    {
         public const byte DIB_RGB_COLORS = 0;
         public const byte DIB_PAL_COLORS = 1;
    }

    public static class UpdateLayerWindowParameter
    {
        public const int  ULW_COLORKEY = 0x00000001;
        public const int  ULW_ALPHA = 0x00000002;
        public const int  ULW_OPAQUE = 0x00000004;
        public const int  ULW_EX_NORESIZE = 0x00000008;
    }


    public static class WindowsLong
    {
        public const int GWL_WNDPROC = -4;
        public const int GWL_HINSTANCE = -6;
        public const int GWL_HWNDPARENT = -8;
        public const int GWL_STYLE = -16;
        public const int GWL_EXSTYLE = -20;
        public const int GWL_USERDATA = -21;
        public const int GWL_ID = -12;
    }
}