public static void DrawAlpha(Graphics gx, Bitmap image, byte transp, int x, int y)
{
using (Graphics gxSrc = Graphics.FromImage(image))
{
IntPtr hdcDst = gx.GetHdc();
IntPtr hdcSrc = gxSrc.GetHdc();
BlendFunction blendFunction = new BlendFunction();
blendFunction.BlendOp = (byte)BlendOperation.AC_SRC_OVER; // Only supported blend operation
blendFunction.BlendFlags = (byte)BlendFlags.Zero; // Documentation says put 0 here
blendFunction.SourceConstantAlpha = transp; // Constant alpha factor
blendFunction.AlphaFormat = (byte)0; // Don't look for per pixel alpha
DrawingAPI.AlphaBlend(hdcDst, x, y, image.Width, image.Height, hdcSrc, 0, 0, image.Width, image.Height, blendFunction);
gx.ReleaseHdc(hdcDst); // Required cleanup to GetHdc()
gxSrc.ReleaseHdc(hdcSrc); // Required cleanup to GetHdc()
}
}
/// <summary>
/// Draws this image into the given Graphics object.
/// If the image contains alpha channel, it will used with the buffer.
/// If an Alpha value is set (> 0), the image will also be alpha blended with the buffer.
/// </summary>
/// <param name="gx">The Graphics object to use for drawing.</param>
/// <param name="bounds">The bounds where to draw.</param>
public void Draw(Graphics gx, Rectangle bounds)
{
ImageInfo imgInfo;
_image.GetImageInfo(out imgInfo);
if (_alpha == 0)
{
// Draw the image, with alpha channel if any
IntPtr hdcDest = gx.GetHdc();
Rectangle dstRect = new Rectangle(bounds.X, bounds.Y, (int)imgInfo.Width + bounds.X, (int)imgInfo.Height + bounds.Y);
_image.Draw(hdcDest, ref dstRect, IntPtr.Zero);
gx.ReleaseHdc(hdcDest);
}
else
{
// Creates buffer on demand
if (_buffer == null)
_buffer = new Bitmap((int)imgInfo.Width, (int)imgInfo.Height, PixelFormat.Format32bppRgb);
using (Graphics gxBuffer = Graphics.FromImage(_buffer))
{
IntPtr hdcBuffer = gxBuffer.GetHdc();
IntPtr hdcOrg = gx.GetHdc();
// Copy original DC into Buffer DC to see the background through the image
DrawingAPI.BitBlt(hdcBuffer, 0, 0, (int)imgInfo.Width, (int)imgInfo.Height, hdcOrg, bounds.X, bounds.Y, DrawingAPI.SRCCOPY);
// Draw the image, with alpha channel if any
Rectangle dstRect = new Rectangle(0, 0, (int)imgInfo.Width, (int)imgInfo.Height);
_image.Draw(hdcBuffer, ref dstRect, IntPtr.Zero);
// Alpha blend image
BlendFunction blendFunction = new BlendFunction();
blendFunction.BlendOp = (byte)BlendOperation.AC_SRC_OVER; // Only supported blend operation
blendFunction.BlendFlags = (byte)BlendFlags.Zero; // Documentation says put 0 here
blendFunction.SourceConstantAlpha = (byte)_alpha; // Constant alpha factor
blendFunction.AlphaFormat = 0; // Don't look for per pixel alpha
DrawingAPI.AlphaBlend(hdcOrg, bounds.X, bounds.Y, bounds.Width, bounds.Height,
hdcBuffer, 0, 0, (int)imgInfo.Width, (int)imgInfo.Height, blendFunction);
gx.ReleaseHdc(hdcOrg); // Required cleanup to GetHdc()
gxBuffer.ReleaseHdc(hdcBuffer); // Required cleanup to GetHdc()
}
}
}
public static extern bool AlphaBlend(IntPtr hdcDest, Int32 nXDest, Int32 nYDest, Int32 nWidthDst, Int32 nHeightDst, IntPtr hdcSrc, Int32 nXSrc, Int32 nYSrc, Int32 nWidthSrc, Int32 nHeightSrc, BlendFunction blendFunction);