55 lines
1.5 KiB
Python
55 lines
1.5 KiB
Python
from profile import Profiler
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from util import gen_point, Side, display
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@Profiler("calc sidedness")
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def sidedness(p1, p2, p3, eps=0.0000001):
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# Find line from p1 to p2, ask where p3 is in relation to this
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y = p3.y * (p2.x - p1.x)
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x = p3.x
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a = (p2.y - p1.y)
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b = p2.y * (p2.x - p1.x) - a * p2.x
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if y - eps < a * x + b < y + eps:
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return Side.ON
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elif y > a * x + b:
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return Side.ABOVE
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return Side.BELOW
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@Profiler("graham_scan")
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def graham_scan(points):
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# A funky issue where both a and b become negative in the sidedness test causes us to have to use
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# Side.ABOVE for both tests, regardless of UH or LH.
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with Profiler("sorting points"):
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sorted_points = sorted(points)
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UH = sorted_points[:2]
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with Profiler("iterating points", excluded=("calc sidedness",)):
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for s in sorted_points[2:]:
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while len(UH) > 1 and (sidedness(UH[-2], UH[-1], s) != Side.ABOVE):
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del UH[-1]
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UH.append(s)
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reversed_list = list(reversed(sorted_points))
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reversed_list.append(UH[0])
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LH = reversed_list[:2]
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with Profiler("iterating points", excluded=("calc sidedness",)):
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for s in reversed_list[2:]:
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while len(LH) > 1 and (sidedness(LH[-2], LH[-1], s) != Side.ABOVE):
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del LH[-1]
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LH.append(s)
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return UH + LH
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if __name__ == '__main__':
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p = [gen_point() for _ in range(30)]
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hull = graham_scan(p)
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display(p, hull)
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