（转）教你实现Winform窗体的四边阴影效果
1.首先我们得有这样一张阴影图片。
2.然后分别有两个窗体去实现这个阴影效果。
- SkinForm - 用于实现阴影的绘制，特性：鼠标可穿透，无法点击，跟随窗体。
-
SkinMain - 主窗体，也是承载控件的容器窗体， 特性：与普通窗体无一区别，移动和拉伸，阴影窗体都会跟随。
3.在SkinMain主窗体的OnVisibleChanged事件中new出阴影窗体
- //绘制层
- private SkinForm skin;
- skin = new SkinForm(this);
- skin.Show(this);
4.阴影窗体中绘制不规则透明图片的代码：
public void SetBits() {
//绘制绘图层背景
Bitmap bitmap = new Bitmap(Main.Width + 10, Main.Height + 10);
Rectangle _BacklightLTRB = new Rectangle(20, 20, 20, 20);//窗体光泽重绘边界
Graphics g = Graphics.FromImage(bitmap);
g.SmoothingMode = SmoothingMode.HighQuality; //高质量
g.PixelOffsetMode = PixelOffsetMode.HighQuality; //高像素偏移质量
ImageDrawRect.DrawRect(g, Properties.Resources.main_light_bkg_top123, ClientRectangle, Rectangle.FromLTRB(_BacklightLTRB.X, _BacklightLTRB.Y, _BacklightLTRB.Width, _BacklightLTRB.Height), 1, 1);
if (!Bitmap.IsCanonicalPixelFormat(bitmap.PixelFormat) || !Bitmap.IsAlphaPixelFormat(bitmap.PixelFormat))
throw new ApplicationException("图片必须是32位带Alhpa通道的图片。");
IntPtr oldBits = IntPtr.Zero;
IntPtr screenDC = Win32.GetDC(IntPtr.Zero);
IntPtr hBitmap = IntPtr.Zero;
IntPtr memDc = Win32.CreateCompatibleDC(screenDC);
try {
Win32.Point topLoc = new Win32.Point(Left, Top);
Win32.Size bitMapSize = new Win32.Size(Width, Height);
Win32.BLENDFUNCTION blendFunc = new Win32.BLENDFUNCTION();
Win32.Point srcLoc = new Win32.Point(0, 0);
hBitmap = bitmap.GetHbitmap(Color.FromArgb(0));
oldBits = Win32.SelectObject(memDc, hBitmap);
blendFunc.BlendOp = Win32.AC_SRC_OVER;
blendFunc.SourceConstantAlpha = Byte.Parse("255");
blendFunc.AlphaFormat = Win32.AC_SRC_ALPHA;
blendFunc.BlendFlags = 0;
Win32.UpdateLayeredWindow(Handle, screenDC, ref topLoc, ref bitMapSize, memDc, ref srcLoc, 0, ref blendFunc, Win32.ULW_ALPHA);
} finally {
if (hBitmap != IntPtr.Zero) {
Win32.SelectObject(memDc, oldBits);
Win32.DeleteObject(hBitmap);
}
Win32.ReleaseDC(IntPtr.Zero, screenDC);
Win32.DeleteDC(memDc);
}
}