Previous Next

                                                       308
           CHAPTER 4                                                                          Graphics



           ShadingType entry. The following sections describe the available shading types
           and the dictionary entries specific to each.

           Type 1 (Function-Based) Shadings

           In type 1 (function-based) shadings, the color at every point in the domain is
           defined by a specified mathematical function. The function need not be smooth
           or continuous. This type is the most general of the available shading types and is
           useful for shadings that cannot be adequately described with any of the other
           types. Table 4.29 shows the shading dictionary entries specific to this type of
           shading, in addition to those common to all shading dictionaries (Table 4.28).

           Note: This type of shading cannot be used with an Indexed color space.

                      TABLE 4.29 Additional entries specific to a type 1 shading dictionary
KEY            TYPE             VALUE

Domain         array            (Optional) An array of four numbers [ xmin xmax ymin ymax ] specifying the
                                rectangular domain of coordinates over which the color function(s) are defined.
                                Default value: [ 0.0 1.0 0.0 1.0 ].

Matrix         array            (Optional) An array of six numbers specifying a transformation matrix mapping
                                the coordinate space specified by the Domain entry into the shading’s target co-
                                ordinate space. For example, to map the domain rectangle [ 0.0 1.0 0.0 1.0 ] to a
                                1-inch square with lower-left corner at coordinates (100, 100) in default user
                                space, the Matrix value would be [ 72 0 0 72 100 100 ]. Default value: the iden-
                                tity matrix [ 1 0 0 1 0 0 ].

Function       function         (Required) A 2-in, n-out function or an array of n 2-in, 1-out functions (where n
                                is the number of color components in the shading dictionary’s color space). Each
                                function’s domain must be a superset of that of the shading dictionary. If the val-
                                ue returned by the function for a given color component is out of range, it is ad-
                                justed to the nearest valid value.

           The domain rectangle (Domain) establishes an internal coordinate space for the
           shading that is independent of the target coordinate space in which it is to be
           painted. The color function(s) (Function) specify the color of the shading at each
           point within this domain rectangle. The transformation matrix (Matrix) then
           maps the domain rectangle into a corresponding rectangle or parallelogram in
           the target coordinate space. Points within the shading’s bounding box (BBox) that
           fall outside this transformed domain rectangle are painted with the shading’s

Previous Next