QuickFont.QBitmap.EmptyAlphaPixel C# (CSharp) Method

        public static unsafe bool EmptyAlphaPixel(BitmapData bitmapData, int px, int py, byte alphaEmptyPixelTolerance)
        {

            byte* addr = (byte*)(bitmapData.Scan0) + bitmapData.Stride * py + px * 4;
            return (*(addr + 3) <= alphaEmptyPixelTolerance);

        }

        private static void RetargetGlyphRectangleInwards(BitmapData bitmapData, QFontGlyph glyph, bool setYOffset, byte alphaTolerance)
        {
            int startX, endX;
            int startY, endY;

            var rect = glyph.rect;

            EmptyDel emptyPix;

            if (bitmapData.PixelFormat == PixelFormat.Format32bppArgb)
                emptyPix = delegate(BitmapData data, int x, int y) { return QBitmap.EmptyAlphaPixel(data, x, y, alphaTolerance); };
            else
                emptyPix = delegate(BitmapData data, int x, int y) { return QBitmap.EmptyPixel(data, x, y); };


            unsafe
            {

                for (startX = rect.X; startX < bitmapData.Width; startX++)
                    for (int j = rect.Y; j < rect.Y + rect.Height; j++)
                        if (!emptyPix(bitmapData, startX, j))
                            goto Done1;
                Done1:

                for (endX = rect.X + rect.Width; endX >= 0; endX--)
                    for (int j = rect.Y; j < rect.Y + rect.Height; j++)
                        if (!emptyPix(bitmapData, endX, j))
                            goto Done2;
                Done2:

                for (startY = rect.Y; startY < bitmapData.Height; startY++)
                    for (int i = startX; i < endX; i++)
                        if (!emptyPix(bitmapData, i, startY))
                            goto Done3;
                            
                Done3:

                for (endY = rect.Y + rect.Height; endY >= 0; endY--)
                    for (int i = startX; i < endX; i++)
                        if (!emptyPix(bitmapData, i, endY))
                            goto Done4;
                Done4:;


            }

            if (endY < startY)
                startY = endY = rect.Y;

            if (endX < startX)
                startX = endX = rect.X;

            glyph.rect = new Rectangle(startX, startY, endX - startX + 1, endY - startY + 1);

            if (setYOffset)
                glyph.yOffset = glyph.rect.Y;

        }