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Source Code for Module pyffi.utils.tangentspace

  1  """A module for tangent space calculation.""" 
  2   
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 39   
 40  from pyffi.utils.mathutils import * 
 41   
 42 -def getTangentSpace(vertices = None, normals = None, uvs = None, 
 43                      triangles = None, orientation = False, 
 44                      orthogonal = True): 
 45      """Calculate tangent space data. 
 46   
 47      >>> vertices = [(0,0,0), (0,1,0), (1,0,0)] 
 48      >>> normals = [(0,0,1), (0,0,1), (0,0,1)] 
 49      >>> uvs = [(0,0), (0,1), (1,0)] 
 50      >>> triangles = [(0,1,2)] 
 51      >>> getTangentSpace(vertices = vertices, normals = normals, uvs = uvs, triangles = triangles) 
 52      ([(0.0, 1.0, 0.0), (0.0, 1.0, 0.0), (0.0, 1.0, 0.0)], [(1.0, 0.0, 0.0), (1.0, 0.0, 0.0), (1.0, 0.0, 0.0)]) 
 53   
 54      :param vertices: A list of vertices (triples of floats/ints). 
 55      :param normals: A list of normals (triples of floats/ints). 
 56      :param uvs: A list of uvs (pairs of floats/ints). 
 57      :param triangles: A list of triangle indices (triples of ints). 
 58      :param orientation: Set to ``True`` to return orientation (this is used by 
 59          for instance Crysis). 
 60      :return: Two lists of vectors, tangents and binormals. If C{orientation} 
 61          is ``True``, then returns an extra list with orientations (containing 
 62          floats which describe the total signed surface of all faces sharing 
 63          the particular vertex). 
 64      """ 
 65   
 66      # validate input 
 67      if len(vertices) != len(normals) or len(vertices) != len(uvs): 
 68          raise ValueError( 
 69              "lists of vertices, normals, and uvs must have the same length") 
 70   
 71      bin = [(0,0,0) for i in xrange(len(vertices)) ] 
 72      tan = [(0,0,0) for i in xrange(len(vertices)) ] 
 73      orientations = [0 for i in xrange(len(vertices))] 
 74   
 75      # calculate tangents and binormals from vertex and texture coordinates 
 76      for t1, t2, t3 in triangles: 
 77          # skip degenerate triangles 
 78          if t1 == t2 or t2 == t3 or t3 == t1: 
 79              continue 
 80   
 81          # get vertices, uvs, and directions of the triangle 
 82          v1 = vertices[t1] 
 83          v2 = vertices[t2] 
 84          v3 = vertices[t3] 
 85          w1 = uvs[t1] 
 86          w2 = uvs[t2] 
 87          w3 = uvs[t3] 
 88          v2v1 = vecSub(v2, v1) 
 89          v3v1 = vecSub(v3, v1) 
 90          w2w1 = vecSub(w2, w1) 
 91          w3w1 = vecSub(w3, w1) 
 92   
 93          # surface of triangle in texture space 
 94          r = w2w1[0] * w3w1[1] - w3w1[0] * w2w1[1] 
 95   
 96          # sign of surface 
 97          r_sign = (1 if r >= 0 else -1) 
 98   
 99          # contribution of this triangle to tangents and binormals 
100          sdir = ( 
101              r_sign * (w3w1[1] * v2v1[0] - w2w1[1] * v3v1[0]), 
102              r_sign * (w3w1[1] * v2v1[1] - w2w1[1] * v3v1[1]), 
103              r_sign * (w3w1[1] * v2v1[2] - w2w1[1] * v3v1[2])) 
104          try: 
105              sdir = vecNormalized(sdir) 
106          except ZeroDivisionError: # catches zero vector 
107              continue # skip triangle 
108          except ValueError: # catches invalid data 
109              continue # skip triangle 
110   
111          tdir = ( 
112              r_sign * (w2w1[0] * v3v1[0] - w3w1[0] * v2v1[0]), 
113              r_sign * (w2w1[0] * v3v1[1] - w3w1[0] * v2v1[1]), 
114              r_sign * (w2w1[0] * v3v1[2] - w3w1[0] * v2v1[2])) 
115          try: 
116              tdir = vecNormalized(tdir) 
117          except ZeroDivisionError: # catches zero vector 
118              continue # skip triangle 
119          except ValueError: # catches invalid data 
120              continue # skip triangle 
121   
122          # vector combination algorithm could possibly be improved 
123          for i in (t1, t2, t3): 
124              tan[i] = vecAdd(tan[i], tdir) 
125              bin[i] = vecAdd(bin[i], sdir) 
126              orientations[i] += r 
127   
128      # convert into orthogonal space 
129      xvec = (1, 0, 0) 
130      yvec = (0, 1, 0) 
131      for i, norm in enumerate(normals): 
132          if abs(1-vecNorm(norm)) > 0.01: 
133              raise ValueError( 
134                  "tangentspace: unnormalized normal in list of normals (%s, norm is %f)" % (norm, vecNorm(norm))) 
135          try: 
136              # turn norm, bin, tan into a base via Gram-Schmidt 
137              bin[i] = vecSub(bin[i], 
138                              vecscalarMul( 
139                                  norm, 
140                                  vecDotProduct(norm, bin[i]))) 
141              bin[i] = vecNormalized(bin[i]) 
142              tan[i] = vecSub(tan[i], 
143                              vecscalarMul( 
144                                  norm, 
145                                  vecDotProduct(norm, tan[i]))) 
146              tan[i] = vecSub(tan[i], 
147                              vecscalarMul( 
148                                  bin[i], 
149                                  vecDotProduct(norm, bin[i]))) 
150              tan[i] = vecNormalized(tan[i]) 
151          except ZeroDivisionError: 
152              # insuffient data to set tangent space for this vertex 
153              # in that case pick a space 
154              bin[i] = vecCrossProduct(xvec, norm) 
155              try: 
156                  bin[i] = vecNormalized(bin[i]) 
157              except ZeroDivisionError: 
158                  bin[i] = vecCrossProduct(yvec, norm) 
159                  bin[i] = vecNormalized(bin[i]) 
160              tan[i] = vecCrossProduct(norm, bin[i]) 
161   
162      # return result 
163      if orientation: 
164          return tan, bin, orientations 
165      else: 
166          return tan, bin 
167   
168  if __name__ == "__main__": 
169      import doctest 
170      doctest.testmod() 
171   

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