Liang Barsky line clipping algorithm in Python

Liang Barsky is a line clipping algorithm that is described the window clipping position to clip a line using some parametric inequalities equation. This algorithm is named after You-Dong Liang and Brian A. Barsky. The efficiency of this algorithm is accurate and more than the Cohen Sutherland line clipping algorithm.

Read: Cohen Sutherland line clipping algorithm in Python

Python code for Liang Barsky line clipping algorithm

import PIL.ImageDraw as ID, PIL.Image as Image
# Requirement
# pip install pillow

# im will show the overlapped between lines
# im1 will show the clipped line
im = Image.new("RGB", (640, 480))
im1 = Image.new("RGB", (640, 480))
draw = ID.Draw(im)
draw2 = ID.Draw(im1)
# polygon(x1, y1, x2, y2, x3, y3, x4, y4)
draw.polygon((200, 200, 400, 200, 400, 300, 200, 300), outline=255)
draw2.polygon((200, 200, 400, 200, 400, 300, 200, 300), outline=255)
# define the windows frame
winMinX = 200
winMaxX = 400
winMinY = 200
winMaxY = 300

# Time interval
# Traveling time between initial and finish position
# Initial position
t1 = [0.0]
# Finish position
t2 = [1.0]

# Handling the float numbers
def ROUND(a):
    return int(a + 0.5)


def clipTest(p, q, t1, t2):
    retVal = 1
    # 4. calculate the value of pk and qk
    if p < 0.0:
        r = float(q) / float(p)
        if r > t2[0]:
            retVal = 0
        elif r > t1[0]:
            t1[0] = r
    elif p > 0.0:
        r = float(q) / float(p)
        if r < t1[0]:
            retVal = 0
        elif r < t2[0]:
            t2[0] = r

    elif q < 0.0:
        retVal = 0

    return retVal


def LiangBarskyAlgo(x1, y1, x2, y2):
    # 3. calculate the values of t1 and t2
    t1 = [0.0]
    t2 = [1.0]
    dx = x2 - x1
    # 2. Calculate the value of p1, p2,p3, p4 and q1, q2, q3,q4.
    if clipTest(-dx, x1 - winMinX, t1, t2):
        if clipTest(dx, winMaxX - x1, t1, t2):
            dy = y2 - y1
            if clipTest(-dy, y1 - winMinY, t1, t2):
                if clipTest(dy, winMaxY - y1, t1, t2):
                    if t2[0] < 1.0:
                        x2 = x1 + t2[0] * dx
                        y2 = y1 + t2[0] * dy

                    if t1[0] > 0.0:
                        x1 = x1 + t1[0] * dx
                        y1 = y1 + t1[0] * dy
                    draw2.line((ROUND(x1), ROUND(y1), ROUND(x2), ROUND(y2)), fill=(0, 255, 0))

# Begin the clipping process
def clip(x1, y1, x2, y2):
    # Draw the intersection line
    draw.line((x1, y1, x2, y2), fill=(0, 255, 0))
    # Perform Liand Barsky Alogorithm to get the clipped line
    LiangBarskyAlgo(x1, y1, x2, y2)

if __name__ == '__main__':
    # 1. Set the endpoints of the line (x1, y1) and (x2, y2).

    # two points need to draw a line

    # point 1
    x1 = int(input("Point1 x1: "))
    y1 = int(input("point1 y1: "))

    # point 2
    x2 = int(input("Point2 x2: "))
    y2 = int(input("Point2 y2: "))

    # Checking if the line need to be clipped or not?
    clip(x1, y1, x2, y2)
    # Show the images and save them locally
    im.show()
    im.save('1. Line with Rectangle overlapped.png')
    im1.show()
    im1.save('2. Clipped line after algorithm applied.png')