Bresenham lines w/o diagonal movement

Question

Is there a modified Bresenham algorithm, where the step from one pixel to the next one isn\'t allowed to be diagonally, just horizontally or vertically? Or any other algorit

Answer 1

I have found that Franz D's answer produces lines that do not closely match the original when close to the horizontal or vertical. While the function below is not perfect, I have found it produces nicer results.

Function BresenhamLineNew : Void( x0 : Int, y0 : Int, x1 : Int, y1 : Int )

    Local dx : Int = Abs( x1 - x0 )
    Local dy : Int = Abs( y1 - y0 )

    Local sx : Int = -1
    Local sy : Int = -1

    If x0 < x1 Then sx = 1
    If y0 < y1 Then sy = 1

    Local err : Int = dx - dy
    Local e2 : Int

    While True

        DrawRect x0, y0, 1, 1

        If x0 = x1 And y0 = y1 Then Exit

        e2 = 2 * err

        If dy > dx
            If e2 > -dy
                err = err - dy
                x0 = x0 + sx
            Elseif e2 < dx
                err = err + dx
                y0 = y0 + sy
            Endif
        Else
            If e2 < dx
                err = err + dx
                y0 = y0 + sy
            Elseif e2 > -dy
                err = err - dy
                x0 = x0 + sx
            Endif
        Endif

    Wend

End Function