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             SECTION 4.6                                                                      Patterns



KEY                 TYPE          VALUE

TilingType          integer       (Required) A code that controls adjustments to the spacing of tiles relative to
                                  the device pixel grid:
                                     1    Constant spacing. Pattern cells are spaced consistently—that is, by a
                                          multiple of a device pixel. To achieve this, the application may need
                                          to distort the pattern cell slightly by making small adjustments to
                                          XStep, YStep, and the transformation matrix. The amount of distor-
                                          tion does not exceed 1 device pixel.
                                     2    No distortion. The pattern cell is not distorted, but the spacing
                                          between pattern cells may vary by as much as 1 device pixel, both
                                          horizontally and vertically, when the pattern is painted. This achieves
                                          the spacing requested by XStep and YStep on average but not neces-
                                          sarily for each individual pattern cell.
                                     3    Constant spacing and faster tiling. Pattern cells are spaced consistently
                                          as in tiling type 1 but with additional distortion permitted to enable a
                                          more efficient implementation.

BBox                rectangle     (Required) An array of four numbers in the pattern coordinate system giving
                                  the coordinates of the left, bottom, right, and top edges, respectively, of the
                                  pattern cell’s bounding box. These boundaries are used to clip the pattern
                                  cell.

XStep               number        (Required) The desired horizontal spacing between pattern cells, measured in
                                  the pattern coordinate system.

YStep               number        (Required) The desired vertical spacing between pattern cells, measured in
                                  the pattern coordinate system. Note that XStep and YStep may differ from the
                                  dimensions of the pattern cell implied by the BBox entry. This allows tiling
                                  with irregularly shaped figures. XStep and YStep may be either positive or
                                  negative but not zero.

Resources           dictionary    (Required) A resource dictionary containing all of the named resources
                                  required by the pattern’s content stream (see Section 3.7.2, “Resource Dic-
                                  tionaries”).

Matrix              array         (Optional) An array of six numbers specifying the pattern matrix (see Section
                                  4.6.1, “General Properties of Patterns”). Default value: the identity matrix
                                  [ 1 0 0 1 0 0 ].

             The pattern dictionary’s BBox, XStep, and YStep values are interpreted in the pat-
             tern coordinate system, and the graphics objects in the pattern’s content stream
             are defined with respect to that coordinate system. The placement of pattern cells

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