clipping.py

from OpenGL.GL import*
from OpenGL.GLU import*
from OpenGL.GLUT import*


def clearscreen():
    glClearColor(0.0, 0.0, 0.0, 0.0)
    gluOrtho2D(-100, 100, -100, 100)
    glClear(GL_COLOR_BUFFER_BIT)

    glPointSize(5.0)


def setpixel(edges, points, rgb):

    glColor3f(rgb[0], rgb[1], rgb[2])
    glBegin(GL_LINES)

    for e in edges:
        for v in e:
            glVertex2fv(points[v])
    glEnd()
    glFlush()


def rectangle(x1, y1, x2, y2):
    edges = [
        [0, 1],
        [1, 2],
        [2, 3],
        [3, 0]
    ]

    points = [
        [x1, y2],
        [x2, y2],
        [x2, y1],
        [x1, y1]
    ]

    rgb = (0.0, 0.0, 1.0)

    setpixel(edges, points, rgb)

# -------line--------------------------------


def line(x1, y1, x2, y2):

    edges = [
        [0, 1],
    ]

    points = [
        [x1, y1],
        [x2, y2]
    ]

    rgb = (1.0, 0.0, 0.0)
    setpixel(edges, points, rgb)


# ENCODE FUNCTION
INSIDE = 0
LEFT = 1
RIGHT = 2
BOTTOM = 4
TOP = 8


def encode(x, y, xl, xr, yb, yt):
    region_code = INSIDE
    if x < xl:
        region_code = region_code | LEFT
    if x > xr:
        region_code = region_code | RIGHT
    if y < yb:
        region_code = region_code | BOTTOM
    if y > yt:
        region_code = region_code | TOP

    return region_code


# Cohen Sutherland
def cohensutherland(x1, y1, x2, y2, xl, xr, yb, yt):
    rectangle(xl, yb, xr, yt)
    line(x1, y1, x2, y2)
    # step1
    r_code1 = encode(x1, y1, xl, xr, yb, yt)
    r_code2 = encode(x2, y2, xl, xr, yb, yt)

    accept = False
    while True:

        # step2
        if r_code1 == 0 and r_code2 == 0:
            # to complete accceptance
            accept = True
            break

        # step3
        elif r_code1 & r_code2 != 0:
            # to complete rejection
            break
        # step4
        else:
            if r_code1 != 0:
                r_codeout = r_code1
            else:
                r_codeout = r_code2


            # intersection point in xl

            if r_codeout & LEFT:
                y = (xl-x1)*(y2-y1)/(x2-x1)+y1
                x = xl    # x1,y1 are the intersecting point of x=xl line

            elif r_codeout & RIGHT:
                y = (xr-x1)*(y2-y1)/(x2-x1)+y1
                x = xr    # x1,y1 are the intersecting point of x=xr line

            elif r_codeout & BOTTOM:
                x = (x2-x1)*(yb-y1)/(y2-y1)+x1
                y = yb     # x1,y1 are the intersecting point of y=yb line

            elif r_codeout & TOP:
                x = (x2-x1)*(yt-y1)/(y2-y1)+x1
                y = yt      # x1,y1 are the intersecting point of y=yt line
            if r_codeout == r_code1:
                x1, y1 = x, y
                r_code1 = encode(x, y, xl, xr, yb, yt)

            else:
                x2, y2 = x, y
                r_code2 = encode(x, y, xl, xr, yb, yt)
    # Here x1,y1 and x2,y2 are the clipped lines and we need to draw this line
    if accept:

        edges = [
            [0, 1]
        ]

        points = [
        [x1, y1],
        [x2, y2]
        ]

        rgb = (0.0, 1.0, 0.0)
        setpixel(edges, points, rgb)
    else:
        print("The given line cannot be clipped!")    


def main():
    choice = 0

    while(choice != 2):
        choice = int(input("Enter\n\t1.Line Clipping \n\t2.exit\n"))

        if choice == 1:

            print("ENTER THE LINE DETAILS")
            x1 = float(input('x1 Coordinate:'))
            y1 = float(input('y1 Coordinate:'))
            x2 = float(input("x2 Coordinate:"))
            y2 = float(input("y2 Coordinate:"))

            print("ENTER THE WINDOW DETAILS")
            xl = float(input('x_Wmin='))
            xr = float(input('x_Wmax='))
            yb = float(input("y_Wmin="))
            yt = float(input("y_Wmax="))

            glutInit()
            glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB)
            glutInitWindowSize(700, 700)
            glutInitWindowPosition(0, 0)
            glutCreateWindow("Line Clipping")
            glutDisplayFunc(lambda: cohensutherland( x1, y1, x2, y2, xl, xr, yb, yt))

            clearscreen()
            glutMainLoop()
        else:
            print("Invalid Choice")


main()