C# WinForm 无锯齿透明异形窗体

通过UpdateLayeredWindow和背景图创建异形窗体

重载CreateParams

        private const int WS_EX_LAYERED = 0x00080000;
        protected override CreateParams CreateParams
        {
            get
            {
                CreateParams cp = base.CreateParams;
                cp.ExStyle |= WS_EX_LAYERED;
                return cp;
            }
        }

设置图片和透明度

        public void SetBitmap(Bitmap bitmap, byte opacity)
        {
            if (bitmap.PixelFormat != PixelFormat.Format32bppArgb)
                throw new ApplicationException("位图必须是32位包含alpha 通道");

            IntPtr screenDc = APIHelper.GetDC(IntPtr.Zero);
            IntPtr memDc = APIHelper.CreateCompatibleDC(screenDc);
            IntPtr hBitmap = IntPtr.Zero;
            IntPtr oldBitmap = IntPtr.Zero;

            try
            {
                hBitmap = bitmap.GetHbitmap(Color.FromArgb(0)); 

                oldBitmap = APIHelper.SelectObject(memDc, hBitmap);

                APIHelper.Size size = new APIHelper.Size(bitmap.Width, bitmap.Height);
                APIHelper.Point pointSource = new APIHelper.Point(0, 0);
                APIHelper.Point topPos = new APIHelper.Point(Left, Top);
                APIHelper.BLENDFUNCTION blend = new APIHelper.BLENDFUNCTION();
                blend.BlendOp = APIHelper.AC_SRC_OVER;
                blend.BlendFlags = 0;
                blend.SourceConstantAlpha = opacity;
                blend.AlphaFormat = APIHelper.AC_SRC_ALPHA;

                APIHelper.UpdateLayeredWindow(Handle, screenDc, ref  topPos, ref  size, memDc, ref  pointSource, 0, ref  blend, APIHelper.ULW_ALPHA);
            }
            finally
            {
                APIHelper.ReleaseDC(IntPtr.Zero, screenDc);
                if (hBitmap != IntPtr.Zero)
                {
                    APIHelper.SelectObject(memDc, oldBitmap);

                    APIHelper.DeleteObject(hBitmap);
                }
                APIHelper.DeleteDC(memDc);
            }
        }

APIHelper :

        [StructLayout(LayoutKind.Sequential)]
        public struct Size
        {
            public Int32 cx;
            public Int32 cy;

            public Size(Int32 x, Int32 y)
            {
                cx = x;
                cy = y;
            }
        }

        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        public struct BLENDFUNCTION
        {
            public byte BlendOp;
            public byte BlendFlags;
            public byte SourceConstantAlpha;
            public byte AlphaFormat;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct Point
        {
            public Int32 x;
            public Int32 y;

            public Point(Int32 x, Int32 y)
            {
                this.x = x;
                this.y = y;
            }
        }

        public const byte AC_SRC_OVER = 0;
        public const Int32 ULW_ALPHA = 2;
        public const byte AC_SRC_ALPHA = 1;

        [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern IntPtr CreateCompatibleDC(IntPtr hDC);

        [DllImport("user32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern IntPtr GetDC(IntPtr hWnd);

        [DllImport("gdi32.dll", ExactSpelling = true)]
        public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObj);

        [DllImport("user32.dll", ExactSpelling = true)]
        public static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);

        [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern int DeleteDC(IntPtr hDC);

        [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern int DeleteObject(IntPtr hObj);

        [DllImport("user32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern int UpdateLayeredWindow(IntPtr hwnd, IntPtr hdcDst, ref Point pptDst, ref Size psize, IntPtr hdcSrc, ref Point pptSrc, Int32 crKey, ref BLENDFUNCTION pblend, Int32 dwFlags);

        [DllImport("gdi32.dll", ExactSpelling = true, SetLastError = true)]
        public static extern IntPtr ExtCreateRegion(IntPtr lpXform, uint nCount, IntPtr rgnData);

使用示例

        public ShapeForm()
        {
            InitializeComponent();
            var bitmap = Properties.Resources.heart;
            SetBitmap(bitmap ,125);
        }

结果展示： 半透明 心形窗体