.png "Cohen Sutherland line clipping algorithm in Python")
The cohen Sutherland algorithm is a line clipping algorithm. This algorithm provides an efficient way to decide the spatial relationship between an arbitrary line, and the clipping window and to find an intersection point.
In this algorithm, one can divide the line clipping process into two phases. Phases are,
1. Identify those lines which intersect the clipping window.
2. Perform the clipping process.
Python code for Cohen Sutherland line clipping algorithm
Code
import PIL.ImageDraw as ID, PIL.Image as Image
# First image for showing line with rectangle border
im = Image.new("RGB", (640, 480))
# Second image for showing clipped line
im1 = Image.new("RGB", (640, 480))
# Drawing the images
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)
# p1 and p4 point will check the draw line.
# p1 and p4 are the rectangle's corner points
p1 = (400.0, 300.0)
p4 = (200.0, 200.0)
def computeCode(x, y):
code = 0
if x < p4[0]:
code = code | 1
elif x > p1[0]:
code = code | 2
if y < p4[1]:
code = code | 4
elif y > p1[1]:
code = code | 8
return code
def CohenSutherlandClippingAlgorithm(x1, y1, x2, y2):
code1 = computeCode(x1, y1)
code2 = computeCode(x2, y2)
accept = False
while True:
if code1 == 0 and code2 == 0:
accept = True
break
elif (code1 & code2) != 0:
break
else:
x = 1.0
y = 1.0
if code1 != 0:
code_out = code1
else:
code_out = code2
if code_out & 8:
x = x1 + (x2 - x1) * (p1[1] - y1) / (y2 - y1)
y = p1[1]
elif code_out & 4:
x = x1 + (x2 - x1) * (p4[1] - y1) / (y2 - y1)
y = p4[1]
elif code_out & 2:
y = y1 + (y2 - y1) * (p1[0] - x1) / (x2 - x1)
x = p1[0]
elif code_out & 1:
y = y1 + (y2 - y1) * (p4[0] - x1) / (x2 - x1)
x = p4[0]
if code_out == code1:
x1 = x
y1 = y
code1 = computeCode(x1, y1)
else:
x2 = x
y2 = y
code2 = computeCode(x2, y2)
if accept:
draw2.line((x1, y1, x2, y2), fill=(0, 0, 255))
else:
print("This line can not be drawn as outside the area")
# Drawing from the input and clipping it using Cohen sutherland algorithm
def clip(x1, y1, x2, y2):
draw.line((x1, y1, x2, y2), fill=(0, 255, 0))
CohenSutherlandClippingAlgorithm(x1, y1, x2, y2)
if __name__ == '__main__':
# Enter two points for 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('Line with Rectangle border.png')
im1.show()
im1.save('Clipped line.png')
Input
Point1 x1: 100
point1 y1: 100
Point2 x2: 600
Point2 y2: 600
Output
 |
| Line with rectangle border (Before applying algorithm) |
 |
| Clipped line (After applying algorithm) |