Source (converted from C) -> http://rosettacode.org/wiki/Bitmap/Bresenham%27s_line_algorithm#C

/// <summary>
        /// Draws a line on an <see cref="GenericImage{T}"/>.
        /// </summary>
        /// <param name="image">
        /// The destination image.
        /// </param>
        /// <param name="x1">
        /// The x position for the start of the line.
        /// </param>
        /// <param name="y1">
        /// The y position for the start of the line.
        /// </param>
        /// <param name="x2">
        /// The x position for the end of the line.
        /// </param>
        /// <param name="y2">
        /// The y position for the end of the line.
        /// </param>
        /// <param name="color">
        /// The color that the line will be drawn with.
        /// </param>
        public static void DrawLine<T>(this GenericImage<T> image, int x1, int y1, int x2, int y2, T color)
        {
            // source (converted from C) -> http://rosettacode.org/wiki/Bitmap/Bresenham%27s_line_algorithm#C
            int dx = Math.Abs(x2 - x1), sx = x1 < x2 ? 1 : -1;
            int dy = Math.Abs(y2 - y1), sy = y1 < y2 ? 1 : -1;
            int err = (dx > dy ? dx : -dy) / 2;

            for (; ; )
            {
                image[x1, y1] = color;
                if (x1 == x2 && y1 == y2) break;
                int e2 = err;
                if (e2 > -dx) { err -= dy; x1 += sx; }
                if (e2 < dy) { err += dx; y1 += sy; }
            }
        }