C#调用GDI+1.1中的函数实现高斯模糊、USM锐化等经典效果。

　　GpStatus WINGDIPAPI GdipBitmapApplyEffect(GpBitmap* bitmap, CGpEffect *effect, RECT *roi, BOOL useAuxData, VOID **auxData, INT *auxDataSize)

      [DllImport( "gdiplus.dll",SetLastError = true, ExactSpelling = true,CharSet = CharSet.Unicode)]
        private static extern int GdipBitmapApplyEffect(IntPtr bitmap, IntPtr effect, ref Rectangle rectOfInterest, bool useAuxData, IntPtr auxData, int auxDataSize);

  /// <summary>
        /// 获取对象的私有字段的值，感谢Aaron Lee Murgatroyd
        /// </summary>
        /// <typeparam name="TResult">字段的类型</typeparam>
        /// <param name="obj">要从其中获取字段值的对象</param>
        /// <param name="fieldName">字段的名称.</param>
        /// <returns>字段的值</returns>
        /// <exception cref="System.InvalidOperationException">无法找到该字段.</exception>
        /// 
        internal static TResult GetPrivateField<TResult>(this object obj, string fieldName)
        {
            if (obj == null) return default(TResult);
            Type ltType = obj.GetType();
            FieldInfo lfiFieldInfo = ltType.GetField( fieldName,System.Reflection.BindingFlags.GetField |System.Reflection.BindingFlags.Instance |System.Reflection.BindingFlags.NonPublic);
            if (lfiFieldInfo != null)
                return (TResult)lfiFieldInfo.GetValue(obj);
            else
                throw new InvalidOperationException(string.Format("Instance field ‘{0}‘ could not be located in object of type ‘{1}‘.",fieldName, obj.GetType().FullName));
        }

  public static IntPtr NativeHandle(this Bitmap Bmp)
        {
            return Bmp.GetPrivateField<IntPtr>("nativeImage");
            /*  用Reflector反编译System.Drawing.Dll可以看到Image类有如下的私有字段
                internal IntPtr nativeImage;
                private byte[] rawData;
                private object userData;
                然后还有一个 SetNativeImage函数
                internal void SetNativeImage(IntPtr handle)
                {
                    if (handle == IntPtr.Zero)
                    {
                        throw new ArgumentException(SR.GetString("NativeHandle0"), "handle");
                    }
                    this.nativeImage = handle;
                }
                这里在看看FromFile等等函数，其实也就是调用一些例如GdipLoadImageFromFile之类的GDIP函数，并把返回的GDIP图像句柄
                通过调用SetNativeImage赋值给变量nativeImage，因此如果我们能获得该值，就可以调用VS2010暂时还没有封装的GDIP函数
                进行相关处理了，并且由于.NET肯定已经初始化过了GDI+，我们也就无需在调用GdipStartup初始化他了。
             */
        }

 /// <summary>
        /// 对图像进行高斯模糊,参考：http://msdn.microsoft.com/en-us/library/ms534057(v=vs.85).aspx
        /// </summary>
        /// <param name="Rect">需要模糊的区域，会对该值进行边界的修正并返回.</param>
        /// <param name="Radius">指定高斯卷积核的半径，有效范围[0，255],半径越大，图像变得越模糊.</param>
        /// <param name="ExpandEdge">指定是否对边界进行扩展，设置为True，在边缘处可获得较为柔和的效果. </param>
            
        public static void GaussianBlur(this Bitmap Bmp, ref Rectangle Rect, float Radius = 10, bool ExpandEdge = false)
        {
            int Result;
            IntPtr BlurEffect;
            BlurParameters BlurPara;
            if ((Radius <0) || (Radius>255)) 
            {
                throw new ArgumentOutOfRangeException("半径必须在[0,255]范围内");
            }
            BlurPara.Radius = Radius ;
            BlurPara.ExpandEdges = ExpandEdge;
            Result = GdipCreateEffect(BlurEffectGuid, out BlurEffect);
            if (Result == 0)
            {
                IntPtr Handle = Marshal.AllocHGlobal(Marshal.SizeOf(BlurPara));
                Marshal.StructureToPtr(BlurPara, Handle, true);
                GdipSetEffectParameters(BlurEffect, Handle, (uint)Marshal.SizeOf(BlurPara));
                GdipBitmapApplyEffect(Bmp.NativeHandle(), BlurEffect, ref Rect, false, IntPtr.Zero, 0);
                // 使用GdipBitmapCreateApplyEffect函数可以不改变原始的图像，而把模糊的结果写入到一个新的图像中
                GdipDeleteEffect(BlurEffect);
                Marshal.FreeHGlobal(Handle);
            }
            else
            {
                throw new ExternalException("不支持的GDI+版本，必须为GDI+1.1及以上版本，且操作系统要求为Win Vista及之后版本.");
            }
        }