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15-Sutherland-Hodgman.py
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15-Sutherland-Hodgman.py
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# Sutherland-Hodgman Polygon Clipping Algorithm
from graphics import*
import numpy as np
win1 = GraphWin("Sutherland-Hodgman: Initial Polygon", 500, 500)
win2 = GraphWin("Sutherland-Hodgman: Clipped Polygon", 500, 500)
left = 0; right = 1; bottom = 2; top = 3
inToIn = 0; inToOut = 1; outToIn = 2; outToOut = 3
def findCase(xmin, xmax, ymin, ymax, boundary, p1, p2):
(x1,y1) = p1
(x2,y2) = p2
if boundary == left:
if x1>=xmin and x2>=xmin:
return inToIn
elif x1>=xmin:
return inToOut
elif x2>=xmin:
return outToIn
else:
return outToOut
elif boundary == right:
if x1<=xmax and x2<=xmax:
return inToIn
elif x1<=xmax:
return inToOut
elif x2<=xmax:
return outToIn
else:
return outToOut
elif boundary == bottom:
if y1>=ymin and y2>=ymin:
return inToIn
elif y1>=ymin:
return inToOut
elif y2>=ymin:
return outToIn
else:
return outToOut
elif boundary == top:
if y1<=ymax and y2<=ymax:
return inToIn
elif y1<=ymax:
return inToOut
elif y2<=ymax:
return outToIn
else:
return outToOut
def findIntersection(xmin, xmax, ymin, ymax, boundary, p1, p2):
(x1,y1) = p1
(x2,y2) = p2
m=0
if x1 != x2:
m = (y2-y1)/(x2-x1)
if boundary == left:
return (xmin, y1+m*(xmin-x1))
elif boundary == right:
return (xmax, y1+m*(xmax-x1))
elif boundary == bottom:
if x1==x2:
return (x1,ymin)
else:
return (x1+(ymin-y1)/m, ymin)
elif boundary == top:
if x1==x2:
return (x1,ymax)
else:
return (x1+(ymax-y1)/m, ymax)
def clipPolygon(xmin, xmax, ymin, ymax, points):
for boundary in range(4):
new_points = []
for i in range(len(points)):
p1 = points[i]
p2 = points[(i+1)%(len(points))]
case = findCase(xmin,xmax,ymin,ymax,boundary,p1,p2)
if case == inToIn:
new_points.append(p2)
elif case == inToOut:
p = findIntersection(xmin,xmax,ymin,ymax,boundary,p1,p2)
new_points.append(p)
elif case == outToIn:
p = findIntersection(xmin,xmax,ymin,ymax,boundary,p1,p2)
new_points.append(p)
new_points.append(p2)
points = new_points
return points
def main():
xmin=150; xmax=350; ymin=150; ymax=350
points = [(250,125),(125,250), (175,275), (240,175)]
r1=Polygon(Point(xmin,ymin), Point(xmin,ymax), Point(xmax,ymax), Point(xmax,ymin))
r1.setOutline("blue")
r1.setWidth(5)
r1.draw(win1)
r2=r1.clone()
r2.draw(win2)
for i in range(len(points)):
(x1,y1) = points[i]
(x2,y2) = points[(i+1)%len(points)]
l = Line(Point(x1,y1), Point(x2,y2))
l.setWidth(3)
l.draw(win1)
new_points = clipPolygon(xmin, xmax, ymin, ymax, points)
for i in range(len(new_points)):
(x1,y1) = new_points[i]
(x2,y2) = new_points[(i+1)%len(new_points)]
l = Line(Point(x1,y1), Point(x2,y2))
l.setWidth(3)
l.draw(win2)
win1.getMouse()
win2.getMouse()
main()