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                                                      292
            CHAPTER 4                                                                        Graphics



            The pattern cell can include graphical elements such as filled areas, text, and sam-
            pled images. Its shape need not be rectangular, and the spacing of tiles can differ
            from the dimensions of the cell itself. When performing painting operations such
            as S (stroke) or f (fill), the application paints the cell on the current page as many
            times as necessary to fill an area. The order in which individual tiles (instances of
            the cell) are painted is unspecified and unpredictable; it is inadvisable for the fig-
            ures on adjacent tiles to overlap.

            The appearance of the pattern cell is defined by a content stream containing the
            painting operators needed to paint one instance of the cell. Besides the usual en-
            tries common to all streams (see Table 3.4 on page 62), this stream’s dictionary
            has the additional entries listed in Table 4.25.

                     TABLE 4.25 Additional entries specific to a type 1 pattern dictionary
KEY                TYPE           VALUE

Type               name           (Optional) The type of PDF object that this dictionary describes; if present,
                                  must be Pattern for a pattern dictionary.

PatternType        integer        (Required) A code identifying the type of pattern that this dictionary de-
                                  scribes; must be 1 for a tiling pattern.

PaintType          integer        (Required) A code that determines how the color of the pattern cell is to be
                                  specified:
                                     1    Colored tiling pattern. The pattern’s content stream specifies the col-
                                          ors used to paint the pattern cell. When the content stream begins ex-
                                          ecution, the current color is the one that was initially in effect in the
                                          pattern’s parent content stream. (This is similar to the definition of
                                          the pattern matrix; see Section 4.6.1, “General Properties of Pat-
                                          terns.”)
                                     2    Uncolored tiling pattern. The pattern’s content stream does not specify
                                          any color information. Instead, the entire pattern cell is painted with
                                          a separately specified color each time the pattern is used. Essentially,
                                          the content stream describes a stencil through which the current col-
                                          or is to be poured. The content stream must not invoke operators that
                                          specify colors or other color-related parameters in the graphics state;
                                          otherwise, an error occurs (see Section 4.5.7, “Color Operators”).
                                          The content stream may paint an image mask, however, since it does
                                          not specify any color information (see “Stencil Masking” on page
                                          350).

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