Previous Next

                                                    319
           SECTION 4.6                                                                   Patterns



           Type 5 Shadings (Lattice-Form Gouraud-Shaded Triangle Meshes)

           Type 5 shadings (lattice-form Gouraud-shaded triangle meshes) are similar to
           type 4, but instead of using free-form geometry, their vertices are arranged in a
           pseudorectangular lattice, which is topologically equivalent to a rectangular grid.
           The vertices are organized into rows, which need not be geometrically linear (see
           Figure 4.19).




 (i, j)              (i, j+1)




(i+1, j)            (i+1, j+1)


                                           Ideal lattice                    Pseudorectangular lattice



                                 FIGURE 4.19 Lattice-form triangle meshes


           Table 4.33 shows the shading dictionary entries specific to this type of shading, in
           addition to those common to all shading dictionaries (Table 4.28) and stream dic-
           tionaries (Table 3.4 on page 62).

           The data stream for a type 5 shading has the same format as for type 4, except that
           type 5 does not use edge flags to define the geometry of the triangle mesh. The
           data for each vertex thus consists of the following values, in the order shown:

             x y c1 … cn

           where
             x and y are the vertex’s horizontal and vertical coordinates
             c1 … cn are its color components

Previous Next