internal static extern bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref POINT pptDst, ref SIZE psize, IntPtr hdcSrc, ref POINT pprSrc, Int32 crKey, ref BLENDFUNCTION pblend, Int32 dwFlags);
protected void UpdateLayeredWindow(Point point, Size size, byte alpha)
{
// Create bitmap for drawing onto
Bitmap memoryBitmap = new Bitmap(size.Width, size.Height, PixelFormat.Format32bppArgb);
using(Graphics g = Graphics.FromImage(memoryBitmap))
{
Rectangle area = new Rectangle(0, 0, size.Width, size.Height);
// Draw the background area
DrawBackground(g, area);
// Draw the actual menu items
DrawAllCommands(g);
// Get hold of the screen DC
IntPtr hDC = User32.GetDC(IntPtr.Zero);
// Create a memory based DC compatible with the screen DC
IntPtr memoryDC = Gdi32.CreateCompatibleDC(hDC);
// Get access to the bitmap handle contained in the Bitmap object
IntPtr hBitmap = memoryBitmap.GetHbitmap(Color.FromArgb(0));
// Select this bitmap for updating the window presentation
IntPtr oldBitmap = Gdi32.SelectObject(memoryDC, hBitmap);
// New window size
SIZE ulwsize;
ulwsize.cx = size.Width;
ulwsize.cy = size.Height;
// New window position
POINT topPos;
topPos.x = point.X;
topPos.y = point.Y;
// Offset into memory bitmap is always zero
POINT pointSource;
pointSource.x = 0;
pointSource.y = 0;
// We want to make the entire bitmap opaque
BLENDFUNCTION blend = new BLENDFUNCTION();
blend.BlendOp = (byte)AlphaFlags.AC_SRC_OVER;
blend.BlendFlags = 0;
blend.SourceConstantAlpha = alpha;
blend.AlphaFormat = (byte)AlphaFlags.AC_SRC_ALPHA;
// Tell operating system to use our bitmap for painting
User32.UpdateLayeredWindow(Handle, hDC, ref topPos, ref ulwsize,
memoryDC, ref pointSource, 0, ref blend,
(int)UpdateLayeredWindowsFlags.ULW_ALPHA);
// Put back the old bitmap handle
Gdi32.SelectObject(memoryDC, oldBitmap);
// Cleanup resources
User32.ReleaseDC(IntPtr.Zero, hDC);
Gdi32.DeleteObject(hBitmap);
Gdi32.DeleteDC(memoryDC);
}
}
internal static extern bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref POINT pptDst, ref SIZE psize, IntPtr hdcSrc, ref POINT pprSrc, Int32 crKey, ref BLENDFUNCTION pblend, Int32 dwFlags);
