public static extern Int32 AlphaBlend(IntPtr hdcDest, Int32 xDest, Int32 yDest, Int32 cxDest, Int32 cyDest,
IntPtr hdcSrc, Int32 xSrc, Int32 ySrc, Int32 cxSrc, Int32 cySrc,
BlendFunction blendFunction);
public static Bitmap CreateAlphaBitmap(byte alpha, Bitmap original)
{
if (alpha < 100)
{
Bitmap b = new Bitmap(original.Width, original.Height);
using (Graphics gxSrc = Graphics.FromImage(b))
using (Graphics resultGx = Graphics.FromImage(original))
{
gxSrc.Clear(Color.Black);
IntPtr hdcDst = resultGx.GetHdc();
IntPtr hdcSrc = gxSrc.GetHdc();
BlendFunction blendFunction = new BlendFunction();
blendFunction.BlendOp = 0; // Only supported blend operation
blendFunction.BlendFlags = 0; // Documentation says put 0 here
blendFunction.SourceConstantAlpha = 50; // Constant alpha factor
blendFunction.AlphaFormat = 0; // Don't look for per pixel alpha
Win32.AlphaBlend(hdcDst, 0, 0, original.Width, original.Height,
hdcSrc, 0, 0, original.Width,
original.Height, blendFunction);
gxSrc.ReleaseHdc(hdcSrc); // Required cleanup to GetHdc()
resultGx.ReleaseHdc(hdcDst); // Required cleanup to GetHdc()
}
b.Dispose();
}
return original;
}
public static Bitmap CreateSnapshot(byte alpha, Point startPosition)
{
Rectangle rect = Screen.PrimaryScreen.Bounds;
rect = new Rectangle(startPosition.X, startPosition.Y, rect.Width - startPosition.X, rect.Height - startPosition.Y);
var result = new Bitmap(rect.Width, rect.Height);
IntPtr deviceContext = Win32.GetDC(IntPtr.Zero);
try
{
using (Graphics resultGx = Graphics.FromImage(result))
{
var resultHdc = resultGx.GetHdc();
Win32.BitBlt(resultHdc, 0, 0, rect.Width, rect.Height, deviceContext, startPosition.X, startPosition.Y, TernaryRasterOperations.SRCCOPY);
resultGx.ReleaseHdc(resultHdc);
}
}
finally
{
Win32.ReleaseDC(IntPtr.Zero, deviceContext);
}
if (alpha < 100)
{
//result = AdjustBrightness(result, (decimal)alpha);
Bitmap b = new Bitmap(rect.Width, result.Height);
using (Graphics gxSrc = Graphics.FromImage(b))
using (Graphics resultGx = Graphics.FromImage(result))
{
gxSrc.Clear(Color.Black);
IntPtr hdcDst = resultGx.GetHdc();
IntPtr hdcSrc = gxSrc.GetHdc();
BlendFunction blendFunction = new BlendFunction();
blendFunction.BlendOp = 0; // Only supported blend operation
blendFunction.BlendFlags = 0; // Documentation says put 0 here
blendFunction.SourceConstantAlpha = 50; // Constant alpha factor
blendFunction.AlphaFormat = 0; // Don't look for per pixel alpha
Win32.AlphaBlend(hdcDst, 0, 0, rect.Width, rect.Height,
hdcSrc, 0, 0, rect.Width,
rect.Height, blendFunction);
gxSrc.ReleaseHdc(hdcSrc); // Required cleanup to GetHdc()
resultGx.ReleaseHdc(hdcDst); // Required cleanup to GetHdc()
}
}
return result;
}
/// <summary>
/// Draw an image with full transparency
/// </summary>
/// <param name="hdc"></param>
/// <param name="transp">Constant alpha factor</param>
/// <param name="x">X coord to draw the image</param>
/// <param name="y">Y coord to draw the image</param>
/// <returns></returns>
private int DrawAlpha(IntPtr hdc, byte transp, int x, int y, int width, int height)
{
var blendFunction = new BlendFunction
{
BlendOp = ((byte)BlendOperation.AC_SRC_OVER), // Only supported blend operation
BlendFlags = 0, // Documentation says put 0 here
SourceConstantAlpha = transp, // Constant alpha factor
AlphaFormat = (byte)0
};
return Win32.AlphaBlend(_hdc, x, y, width, height, hdc, 0, 0, width, height, blendFunction);
}
