public void SetBitmap(Bitmap bitmap, byte opacity)
{
bmpbase = bitmap.Clone() as Bitmap;
if (HasChildren && DoDrawChildren)
{
DrawChildren(bmpbase);
}
/*
* if (bitmap.PixelFormat != PixelFormat.Format32bppPArgb)
* throw new ApplicationException("The bitmap must be 32ppp with alpha-channel.");
*/
// The ideia 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.
Bounds = new Rectangle(Location, bmpbase.Size);
Size = bmpbase.Size;
screenDc = User32.GetDC(this.Handle); // was IntPtr.Zero
memDc = Gdi32.CreateCompatibleDC(screenDc);
hBitmap = IntPtr.Zero;
oldBitmap = IntPtr.Zero;
//ClientSize = bitmap.Size;
try {
hBitmap = bmpbase.GetHbitmap(Color.FromArgb(0)); // Color.FromArgb(0);grab a GDI handle from this GDI+ bitmap
oldBitmap = Gdi32.SelectObject(memDc, hBitmap);
Size size = new Size(bmpbase.Width, bmpbase.Height);
Point pointSource = new Point(0, 0);
Point topPos = Location;
Gdi32.BLENDFUNCTION blend = new Gdi32.BLENDFUNCTION();
blend.BlendOp = Gdi32.AC_SRC_OVER;
blend.BlendFlags = 0;
blend.SourceConstantAlpha = opacity;
blend.AlphaFormat = Gdi32.AC_SRC_ALPHA;
User32.UpdateLayeredWindow(Handle, screenDc, ref topPos, ref size, memDc, ref pointSource, 0, ref blend, Gdi32.ULW_ALPHA);
}
finally {
User32.ReleaseDC(IntPtr.Zero, screenDc);
if (hBitmap != IntPtr.Zero)
{
Gdi32.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 Win GDI and it's working fine without any resource leak.
Gdi32.DeleteObject(hBitmap);
}
Gdi32.DeleteDC(memDc);
}
}
[DllImport(user32, ExactSpelling = true, SetLastError = true)] public static extern Bool UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref Point pptDst, ref Size psize, IntPtr hdcSrc, ref Point pprSrc, Int32 crKey, ref Gdi32.BLENDFUNCTION pblend, Gdi32.BlendMode dwFlags);
