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annotate orpg/mapper/map_utils.py @ 4:c0da99091e1d grumpy-goblin

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author sirebral
date Wed, 15 Jul 2009 02:09:11 -0500
parents 4385a7d0efd1
children 072ffc1d466f
rev   line source
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1 #------------------------------------------------
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2 # file: map_utils.py
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3 #
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4 # This file contains generic utility functions
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5 # for use in the openrpg mapping system
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6 # -----------------------------------------------
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7
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8 import math
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9
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10 #-----------------------------------------------------------------------
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11 # distance_between()
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12 # Returns the distance between two points
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13 #-----------------------------------------------------------------------
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14 def distance_between( x1, y1, x2, y2 ):
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15 "Returns the distance between two points"
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16 dx = x2 - x1
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17 dy = y2 - y1
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18 return math.sqrt( dx*dx + dy*dy )
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19
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20 #-----------------------------------------------------------------------
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21 # proximity_test()
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22 # Tests if 'test_point' (T) is close (within 'threshold' units) to the
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23 # line segment 'start_point' to 'end_point' (PQ).
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24 #
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25 # The closest point (R) to T on the line PQ is given by:
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26 # R = P + u (Q - P)
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27 # TR is perpendicular to PQ so:
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28 # (T - R) dot (Q - P) = 0
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29 # Solving these two equations gives the equation for u (see below).
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30 #
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31 # If u < 0 or u > 1 then R is not within the line segment and we simply
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32 # test against point P or Q.
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33 #-----------------------------------------------------------------------
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34 def proximity_test( start_point, end_point, test_point, threshold ):
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35 "Test if a point is close to a line segment"
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36 x1,y1 = start_point
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37 x2,y2 = end_point
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38 xt,yt = test_point
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39 x1 = float(x1)
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40 x2 = float(x2)
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41 y1 = float(y1)
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42 y2 = float(y2)
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43 xt = float(xt)
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44 yt = float(yt)
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45
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46 # Coincident points?
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47 if x1 == x2 and y1 == y2:
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48 d = distance_between(xt, yt, x1, y1)
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49 else:
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50 dx = x2 - x1
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51 dy = y2 - y1
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52 u = ((xt - x1) * dx + (yt - y1) * dy) / (dx*dx + dy*dy)
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53 if u < 0:
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54 d = distance_between(xt, yt, x1, y1)
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55 elif u > 1:
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56 d = distance_between(xt, yt, x2, y2)
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57 else:
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58 xr = x1 + u * dx
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59 yr = y1 + u * dy
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60 d = distance_between(xt, yt, xr, yr)
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61 return d <= threshold