//
// Copyright © 2002-2004 Rui Godinho Lopes <rui@ruilopes.com>
// All rights reserved.
//
// This source file(s) may be redistributed unmodified by any means
// PROVIDING they are not sold for profit without the authors expressed
// written consent, and providing that this notice and the authors name
// and all copyright notices remain intact.
//
// Any use of the software in source or binary forms, with or without
// modification, must include, in the user documentation ("About" box and
// printed documentation) and internal comments to the code, notices to
// the end user as follows:
//
// "Portions Copyright © 2002-2004 Rui Godinho Lopes"
//
// An email letting me know that you are using it would be nice as well.
// That's not much to ask considering the amount of work that went into
// this.
//
// THIS SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
// EXPRESS OR IMPLIED. USE IT AT YOUT OWN RISK. THE AUTHOR ACCEPTS NO
// LIABILITY FOR ANY DATA DAMAGE/LOSS THAT THIS PRODUCT MAY CAUSE.
//

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace PerPixelForm
{
    // class that exposes needed win32 gdi functions.
    public class Win32
    {
        public enum Bool
        {
            False = 0,
            True
        };


        [StructLayout(LayoutKind.Sequential)]
        public struct Point
        {
            public Int32 x;
            public Int32 y;

            public Point(Int32 x, Int32 y) { this.x = x; this.y = y; }
        }


        [StructLayout(LayoutKind.Sequential)]
        public struct Size
        {
            public Int32 cx;
            public Int32 cy;

            public Size(Int32 cx, Int32 cy) { this.cx = cx; this.cy = cy; }
        }


        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        struct ARGB
        {
            public byte Blue;
            public byte Green;
            public byte Red;
            public byte Alpha;
        }


        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        public struct BLENDFUNCTION
        {
            public byte BlendOp;
            public byte BlendFlags;
            public byte SourceConstantAlpha;
            public byte AlphaFormat;
        }


        public const Int32 ULW_COLORKEY = 0x00000001;
        public const Int32 ULW_ALPHA = 0x00000002;
        public const Int32 ULW_OPAQUE = 0x00000004;

        public const byte AC_SRC_OVER = 0x00;
        public const byte AC_SRC_ALPHA = 0x01;


        [DllImport("user32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern Bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref Point pptDst, ref Size psize, IntPtr hdrc, ref Point pprSrc, Int32 crKey, ref BLENDFUNCTION pblend, Int32 dwFlags);

        [DllImport("user32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern IntPtr GetDC(IntPtr hWnd);

        [DllImport("user32.dll", ExactSpelling = true)]
        public static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);

        [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern IntPtr CreateCompatibleDC(IntPtr hDC);

        [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern Bool DeleteDC(IntPtr hdc);

        [DllImport("gdi32.dll", ExactSpelling = true)]
        public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);

        [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern Bool DeleteObject(IntPtr hObject);
    }



    /// <para>Your PerPixel form should inherit this class</para>
    /// <author><name>Rui Godinho Lopes</name><email>rui@ruilopes.com</email></author>
    public class PerPixelAlphaForm : Form
    {
        public PerPixelAlphaForm()
        {
            // This form should not have a border or else Windows will clip it.
            FormBorderStyle = FormBorderStyle.None;
        }


        /// <para>Changes the current bitmap.</para>
        public void SetBitmap(Bitmap bitmap)
        {
            SetBitmap(bitmap, 255);

        }


        /// <para>Changes the current bitmap with a custom opacity level.  Here is where all happens!</para>
        public void SetBitmap(Bitmap bitmap, byte opacity)
        {
            if (bitmap.PixelFormat != PixelFormat.Format32bppArgb)
                throw new ApplicationException("The bitmap must be 32ppp with alpha-channel.");

            // The idea of this is very simple,
            // 1. Create a compatible DC with screen;
            // 2. Select the bitmap with 32bpp with alpha-channel in the compatible DC;
            // 3. Call the UpdateLayeredWindow.

            IntPtr screenDc = Win32.GetDC(IntPtr.Zero);
            IntPtr memDc = Win32.CreateCompatibleDC(screenDc);
            IntPtr hBitmap = IntPtr.Zero;
            IntPtr oldBitmap = IntPtr.Zero;

            try
            {
                hBitmap = bitmap.GetHbitmap(Color.FromArgb(0));  // grab a GDI handle from this GDI+ bitmap
                oldBitmap = Win32.SelectObject(memDc, hBitmap);

                Win32.Size size = new Win32.Size(bitmap.Width, bitmap.Height);
                Win32.Point pointSource = new Win32.Point(0, 0);
                Win32.Point topPos = new Win32.Point(Left, Top);
                Win32.BLENDFUNCTION blend = new Win32.BLENDFUNCTION();
                blend.BlendOp = Win32.AC_SRC_OVER;
                blend.BlendFlags = 0;
                blend.SourceConstantAlpha = opacity;
                blend.AlphaFormat = Win32.AC_SRC_ALPHA;

                Win32.UpdateLayeredWindow(Handle, screenDc, ref topPos, ref size, memDc, ref pointSource, 0, ref blend, Win32.ULW_ALPHA);
            }
            finally
            {
                Win32.ReleaseDC(IntPtr.Zero, screenDc);
                if (hBitmap != IntPtr.Zero)
                {
                    Win32.SelectObject(memDc, oldBitmap);
                    //Windows.DeleteObject(hBitmap); // The documentation says that we have to use the Windows.DeleteObject... but since there is no such method I use the normal DeleteObject from Win32 GDI and it's working fine without any resource leak.
                    Win32.DeleteObject(hBitmap);
                }
                Win32.DeleteDC(memDc);
            }
        }


        protected override CreateParams CreateParams
        {
            get
            {
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= 0x00080000; // This form has to have the WS_EX_LAYERED extended style
                return cp;
            }
        }
    }
}