public static void SelectBitmapIntoLayerWindow(Form win, Bitmap bitmap, byte opacity)
{
// 判断位图是否包含Alpha通道
if (bitmap.PixelFormat != PixelFormat.Format32bppArgb)
{
throw new ApplicationException("必须是带Alpha通道的32位位图");
}
// 获取设备上下文DC
IntPtr screenDc = Win32.GetDC(IntPtr.Zero);
IntPtr memDc = Win32.CreateCompatibleDC(screenDc);
IntPtr hBitmap = IntPtr.Zero;
IntPtr hOldBitmap = IntPtr.Zero;
try
{
// 获取插入到设备上下文位图的句柄
hBitmap = bitmap.GetHbitmap(Color.FromArgb(0));
hOldBitmap = Win32.SelectObject(memDc, hBitmap);
// 设置层叠窗口更新的参数
Size newSize = new Size(bitmap.Width, bitmap.Height); // 设置窗口同位图大小
Point sourceLocation = new Point(0, 0);
Point newLocation = new Point(win.Left, win.Top);
BlendFunction blend = new BlendFunction();
blend.BlendOp = (byte)BlendOp.AC_SRC_OVER; // 仅支持32位位图
blend.BlendFlags = 0; // 总是 0
blend.SourceConstantAlpha = opacity; // 像素的Alpha通道值
blend.AlphaFormat = (byte)BlendOp.AC_SRC_ALPHA; // 仅支持含Alpha通道的位置
// 更新层叠窗口
Win32.UpdateLayeredWindow(win.Handle,
screenDc, ref newLocation, ref newSize, memDc, ref sourceLocation, 0, ref blend, (int)ULWPara.ULW_ALPHA);
}
finally
{
// 释放设备上下文
Win32.ReleaseDC(IntPtr.Zero, screenDc);
if (hBitmap != IntPtr.Zero)
{
Win32.SelectObject(memDc, hOldBitmap);
Win32.DeleteObject(hBitmap); // 删除GDI+位图
}
Win32.DeleteDC(memDc);
}
}
/// <summary>
/// 使用AlphaBlend API绘制带Alpha通道的半透明图片
/// </summary>
/// <param name="gx">Destination graphics</param>
/// <param name="image">The image to draw</param>
/// <param name="transparency">transparent factor</param>
/// <param name="x">X Location</param>
/// <param name="y">Y Location</param>
public static void DrawAlpha(this Graphics gx, Bitmap image, byte transparency, 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 = transparency; // Constant alpha factor
blendFunction.AlphaFormat = (byte)0; // Don't look for per pixel alpha
Win32.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()
}
}
extern public static 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 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);
