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                                             327
SECTION 4.6                                                               Patterns




                  TABLE 4.35 Data values in a Coons patch mesh
EDGE FLAG      NEXT SET OF DATA VALUES

f=0            x1 y1 x2 y2 x3 y3 x4 y4 x5 y5 x6 y6
               x7 y7 x8 y8 x9 y9 x10 y10 x11 y11 x12 y12
               c1 c2 c3 c4
               New patch; no implicit values

f=1            x5 y5 x6 y6 x7 y7 x8 y8 x9 y9 x10 y10 x11 y11 x12 y12
               c3 c4
               Implicit values:
               (x1 , y1 ) = (x4 , y4 ) previous        c1 = c2 previous
               (x2 , y2 ) = (x5 , y5 ) previous        c2 = c3 previous
               (x3 , y3 ) = (x6 , y6 ) previous
               (x4 , y4 ) = (x7 , y7 ) previous

f=2            x5 y5 x6 y6 x7 y7 x8 y8 x9 y9 x10 y10 x11 y11 x12 y12
               c3 c4
               Implicit values:
               (x1 , y1 ) = (x7 , y7 ) previous        c1 = c3 previous
               (x2 , y2 ) = (x8 , y8 ) previous        c2 = c4 previous
               (x3 , y3 ) = (x9 , y9 ) previous
               (x4 , y4 ) = (x10 , y10 ) previous

f=3            x5 y5 x6 y6 x7 y7 x8 y8 x9 y9 x10 y10 x11 y11 x12 y12
               c3 c4
               Implicit values:
               (x1 , y1 ) = (x10 , y10 ) previous      c1 = c4 previous
               (x2 , y2 ) = (x11 , y11 ) previous      c2 = c1 previous
               (x3 , y3 ) = (x12 , y12 ) previous
               (x4 , y4 ) = (x1 , y1 ) previous


Type 7 Shadings (Tensor-Product Patch Meshes)

Type 7 shadings (tensor-product patch meshes) are identical to type 6, except that
they are based on a bicubic tensor-product patch defined by 16 control points in-
stead of the 12 control points that define a Coons patch. The shading dictionaries
representing the two patch types differ only in the value of the ShadingType entry
and in the number of control points specified for each patch in the data stream.

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