;
// class that exposes needed win32 gdi functions.
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 hdcSrc, 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>
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 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.
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;
}
}
}
