计算图片不透明轨迹

/// Calculate the graphics path that representing the figure in the bitmap
        /// excluding the transparent color which is the top left pixel.
        /// //计算位图中不透明部分的边界
        ///
        /// The Bitmap object to calculate our graphics path from
        /// Calculated graphics path
        private static GraphicsPath CalculateControlGraphicsPath(Bitmap bitmap)
        {
            // Create GraphicsPath for our bitmap calculation
            //创建 GraphicsPath
            GraphicsPath graphicsPath = new GraphicsPath();
            // Use the top left pixel as our transparent color
            //使用左上角的一点的颜色作为我们透明色
            Color colorTransparent = bitmap.GetPixel(0, 0);
            // This is to store the column value where an opaque pixel is first found.
            // This value will determine where we start scanning for trailing opaque pixels.
            //第一个找到点的X
            int colOpaquePixel = 0;
            // Go through all rows (Y axis)
            // 偏历所有行（Y方向）
            for (int row = 0; row < bitmap.Height; row++)
            {
                // Reset value
                //重设
                colOpaquePixel = 0;
                // Go through all columns (X axis)
                //偏历所有列（X方向）
                for (int col = 0; col < bitmap.Width; col++)
                {
                    // If this is an opaque pixel, mark it and search for anymore trailing behind
                    //如果是不需要透明处理的点则标记，然后继续偏历
                    if (bitmap.GetPixel(col, row) != colorTransparent)
                    {
                        // Opaque pixel found, mark current position
                        //记录当前
                        colOpaquePixel = col;
                        // Create another variable to set the current pixel position
                        //建立新变量来记录当前点
                        int colNext = col;
                        // Starting from current found opaque pixel, search for anymore opaque pixels
                        // trailing behind, until a transparent   pixel is found or minimum width is reached
                        ///从找到的不透明点开始，继续寻找不透明点,一直到找到或则达到图片宽度
                        for (colNext = colOpaquePixel; colNext < bitmap.Width; colNext++)
                            if (bitmap.GetPixel(colNext, row) == colorTransparent)
                                break;
                        // Form a rectangle for line of opaque   pixels found and add it to our graphics path
                        //将不透明点加到graphics path
                        graphicsPath.AddRectangle(new Rectangle(colOpaquePixel, row, colNext - colOpaquePixel, 1));
                        // No need to scan the line of opaque pixels just found
                        col = colNext;
                    }
                }
            }
            // Return calculated graphics path
            return graphicsPath;
        }