CC calculation _draw_line

Function

def _draw_line(surf, color, x1, y1, x2, y2):
    '''draw a non-horizontal line (without anti-aliasing).'''
    # Variant of https://en.wikipedia.org/wiki/Bresenham's_line_algorithm
    #
    # This strongly differs from craw.c implementation, because we use a
    # "slope" variable (instead of delta_x and delta_y) and a "error" variable.
    # And we can not do pointer-arithmetic with "BytesPerPixel", like in
    # the C-algorithm.
    if x1 == x2:
        # This case should not happen...
        raise ValueError

    slope = abs((y2 - y1) / (x2 - x1))
    error = 0.0

    if slope < 1:
        # Here, it's a rather horizontal line

        # 1. check in which octants we are & set init values
        if x2 < x1:
            x1, x2 = x2, x1
            y1, y2 = y2, y1
        y = y1
        dy_sign = 1 if (y1 < y2) else -1

        # 2. step along x coordinate
        for x in range(x1, x2 + 1):
            set_at(surf, x, y, color)
            error += slope
            if error >= 0.5:
                y += dy_sign
                error -= 1
    else:
        # Case of a rather vertical line

        # 1. check in which octants we are & set init values
        if y1 > y2:
            x1, x2 = x2, x1
            y1, y2 = y2, y1
        x = x1
        slope = 1 / slope
        dx_sign = 1 if (x1 < x2) else -1

        # 2. step along y coordinate
        for y in range(y1, y2 + 1):
            set_at(surf, x, y, color)
            error += slope
            if error >= 0.5:
                x += dx_sign
                error -= 1

Control flow graph

def _draw_line(surf, color, x1, y1, x2, y2):
    #1
    if x1 == x2:
        #3
        raise ValueError
    #2
    slope = abs((y2 - y1) / (x2 - x1))
    error = 0.0
    if slope < 1:
        #5
        if x2 < x1:
            #8
            x1, x2 = x2, x1
            y1, y2 = y2, y1
        #7
        y = y1
        ##dy_sign = 1 if (y1 < y2) else -1
        if (y1 < y2):
            #10
            dy_sign = 1
        else:
            #11
            dy_sign = -1
        #9
        for x in range(x1, x2 + 1):
            #13
            set_at(surf, x, y, color)
            error += slope
            if error >= 0.5:
                #15
                y += dy_sign
                error -= 1
            #14
        #12
    else:
        #6
        if y1 > y2:
            #17
            x1, x2 = x2, x1
            y1, y2 = y2, y1
        #16
        x = x1
        slope = 1 / slope
        ##dx_sign = 1 if (x1 < x2) else -1
        if (x1 < x2):
            #19
            dx_sign = 1
        else:
            #20
            dx_sign = -1
        #18
        for y in range(y1, y2 + 1):
            #22
            set_at(surf, x, y, color)
            error += slope
            if error >= 0.5:
                #24
                x += dx_sign
                error -= 1
            #23
        #21
    #4

https://i.imgur.com/fBuIwBF.png

Calculation

• Edges = 34
• Nodes = 24
• Connected components = 1
  34 - 24 + 2*1 = 12

CC from hand calculation = 12

CC from Lizard = 11