using System;

using System.Collections.Generic;

using System.Text;

using System.Drawing;

using System.Runtime.InteropServices;

using System.Drawing.Imaging;

namespace Aga.Controls

{

	public static class BitmapHelper

	{

		[StructLayout(LayoutKind.Sequential)]

		private struct PixelData

		{

			public byte B;

			public byte G;

			public byte R;

			public byte A;

		}

		public static void SetAlphaChanelValue(Bitmap image, byte value)

		{

			if (image == null)

				throw new ArgumentNullException("image");

			if (image.PixelFormat != PixelFormat.Format32bppArgb)

				throw new ArgumentException("Wrong PixelFormat");

			BitmapData bitmapData = image.LockBits(new Rectangle(0, 0, image.Width, image.Height),

									 ImageLockMode.ReadWrite, PixelFormat.Format32bppArgb);

			unsafe

			{

				PixelData* pPixel = (PixelData*)bitmapData.Scan0;

				for (int i = 0; i < bitmapData.Height; i++)

				{

					for (int j = 0; j < bitmapData.Width; j++)

					{

						pPixel->A = value;

						pPixel++;

					}

					pPixel += bitmapData.Stride - (bitmapData.Width * 4);

				}

			}

			image.UnlockBits(bitmapData);

		}

	}

}