System.Windows.Media.Imaging.WriteableBitmapExtensions.Blit C# (CSharp) Метод

        public static void Blit(BitmapContext destContext, int dpw, int dph, Rect destRect, BitmapContext srcContext, Rect sourceRect, int sourceWidth)
        {
            const BlendMode blendMode = BlendMode.Alpha;

            int dw = (int)destRect.Width;
            int dh = (int)destRect.Height;

            Rect intersect = new Rect(0, 0, dpw, dph);
            intersect.Intersect(destRect);
            if (intersect.IsEmpty)
            {
                return;
            }
#if WPF
            var isPrgba = srcContext.Format == PixelFormats.Pbgra32 || srcContext.Format == PixelFormats.Prgba64 || srcContext.Format == PixelFormats.Prgba128Float;
#endif

            var sourcePixels = srcContext.Pixels;
            var destPixels = destContext.Pixels;
            int sourceLength = srcContext.Length;
            int sourceIdx = -1;
            int px = (int)destRect.X;
            int py = (int)destRect.Y;
            int x;
            int y;
            int idx;
            double ii;
            double jj;
            int sr = 0;
            int sg = 0;
            int sb = 0;
            int dr, dg, db;
            int sourcePixel;
            int sa = 0;
            int da;

            var sw = (int)sourceRect.Width;
            var sdx = sourceRect.Width / destRect.Width;
            var sdy = sourceRect.Height / destRect.Height;
            int sourceStartX = (int)sourceRect.X;
            int sourceStartY = (int)sourceRect.Y;
            int lastii, lastjj;
            lastii = -1;
            lastjj = -1;
            jj = sourceStartY;
            y = py;
            for (var j = 0; j < dh; j++)
            {
                if (y >= 0 && y < dph)
                {
                    ii = sourceStartX;
                    idx = px + y * dpw;
                    x = px;
                    sourcePixel = sourcePixels[0];

                    // Pixel by pixel copying
                    for (var i = 0; i < dw; i++)
                    {
                        if (x >= 0 && x < dpw)
                        {
                            if ((int)ii != lastii || (int)jj != lastjj)
                            {
                                sourceIdx = (int)ii + (int)jj * sourceWidth;
                                if (sourceIdx >= 0 && sourceIdx < sourceLength)
                                {
                                    sourcePixel = sourcePixels[sourceIdx];
                                    sa = ((sourcePixel >> 24) & 0xff);
                                    sr = ((sourcePixel >> 16) & 0xff);
                                    sg = ((sourcePixel >> 8) & 0xff);
                                    sb = ((sourcePixel) & 0xff);
                                }
                                else
                                {
                                    sa = 0;
                                }
                            }

                            if (sa > 0)
                            {
                                int destPixel = destPixels[idx];
                                da = ((destPixel >> 24) & 0xff);
                                if ((sa == 255 || da == 0))
                                {
                                    destPixels[idx] = sourcePixel;
                                }
                                else
                                {
                                    dr = ((destPixel >> 16) & 0xff);
                                    dg = ((destPixel >> 8) & 0xff);
                                    db = ((destPixel) & 0xff);
                                    var isa = 255 - sa;
#if NETFX_CORE
                                    // Special case for WinRT since it does not use pARGB (pre-multiplied alpha)
                                    destPixel = ((da & 0xff) << 24) |
                                                ((((sr * sa + isa * dr) >> 8) & 0xff) << 16) |
                                                ((((sg * sa + isa * dg) >> 8) & 0xff) <<  8) |
                                                (((sb * sa + isa * db) >> 8) & 0xff);
#elif WPF
                                    if (isPrgba)
                                    {
                                        destPixel = ((da & 0xff) << 24) |
                                                    (((((sr << 8) + isa * dr) >> 8) & 0xff) << 16) |
                                                    (((((sg << 8) + isa * dg) >> 8) & 0xff) << 8) |
                                                     ((((sb << 8) + isa * db) >> 8) & 0xff);
                                    }
                                    else
                                    {
                                        destPixel = ((da & 0xff) << 24) |
                                                    (((((sr * sa) + isa * dr) >> 8) & 0xff) << 16) |
                                                    (((((sg * sa) + isa * dg) >> 8) & 0xff) << 8) |
                                                     ((((sb * sa) + isa * db) >> 8) & 0xff);
                                    }
#else
                                    destPixel = ((da & 0xff) << 24) |
                                                (((((sr << 8) + isa * dr) >> 8) & 0xff) << 16) |
                                                (((((sg << 8) + isa * dg) >> 8) & 0xff) << 8) |
                                                 ((((sb << 8) + isa * db) >> 8) & 0xff);
#endif
                                    destPixels[idx] = destPixel;
                                }
                            }
                        }
                        x++;
                        idx++;
                        ii += sdx;
                    }
                }
                jj += sdy;
                y++;
            }

        }