/// <summary>
/// 设置图象
/// </summary>
protected void SetBitmap(Bitmap bitmap, byte opacity = 255)
{
if (bitmap.PixelFormat != PixelFormat.Format32bppArgb)
{
throw new ApplicationException("The bitmap must be 32bpp with alpha-channel.");
}
this.ClientSize = new Size(bitmap.Width, bitmap.Height);
// 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 = GetDC(IntPtr.Zero);
IntPtr memDc = 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 = SelectObject(memDc, hBitmap);
ExtSize size = new ExtSize(bitmap.Width, bitmap.Height);
ExtPoint pointSource = new ExtPoint(0, 0);
ExtPoint topPos = new ExtPoint(this.Left, this.Top);
ExtBlendFunction blend = new ExtBlendFunction
{
BlendOp = AC_SRC_OVER,
BlendFlags = 0,
SourceConstantAlpha = opacity,
AlphaFormat = AC_SRC_ALPHA
};
UpdateLayeredWindow(Handle, screenDc, ref topPos, ref size, memDc, ref pointSource, 0, ref blend, ULW_ALPHA);
}
finally
{
ReleaseDC(IntPtr.Zero, screenDc);
if (hBitmap != IntPtr.Zero)
{
SelectObject(memDc, oldBitmap);
// 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.
//
// Windows.DeleteObject(hBitmap);
DeleteObject(hBitmap);
}
DeleteDC(memDc);
}
bitmap.Dispose();
}
private static extern Bool UpdateLayeredWindow(IntPtr hWnd, IntPtr hdcDst, ref ExtPoint pptDst,
ref ExtSize psize, IntPtr hDcSrc, ref ExtPoint pprSrc, int crKey, ref ExtBlendFunction pblend, int dwFlags);
