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Inside Macintosh: QuickDraw GX Environment and Utilities /

Chapter 7 - QuickDraw GX Stream Format / QuickDraw GX Stream Format Reference

Style Object Omit Byte Constants and Data Types

Pattern Style Omit Byte Masks and Shifts

The gxOmitPatternMask1 enumeration defines which bits in an omit byte correspond to the data compression opcodes for the field descriptors in the gxPatternRecord structure. The sequence of data is also defined. The omit byte and its related data sequence is given in the section "Pattern Data" beginning on page 7-38.

enum gxOmitPatternMask1{
      gxOmitPatternAttributesMask   = 0xC0,
      gxOmitPatternShapeMask        = 0x30,
      gxOmitPatternUXMask           = 0x0C,
      gxOmitPatternUYMask           = 0x03
   };

Constant descriptions

gxOmitPatternAttributesMask

The mask used to select the data compression bits for the attributes field descriptor.

gxOmitPatternShapeMask

The mask used to select the data compression bits for the pattern field descriptor.

gxOmitPatternUXMask

The mask used to select the data compression bits for the ux field descriptor.

gxOmitPatternUYMask

The mask used to select the data compression bits for the uy field descriptor.

Once one of the gxOmitPatternMask1 enumeration masks has been used to select data compression bits for one of the field descriptors in the gxPatternRecord structure, the corresponding bit shift from the gxOmitPatternShift1 enumeration can be applied to the selected bits. The selected bits must be moved to the right by the indicated number of bits to isolate the data compression bits so that they can be compared to other values.

enum gxOmitPatternShift1 {
   gxOmitPatternAttributesShift  = 6,
   gxOmitPatternShapeShift       = 4,
   gxOmitPatternUXShift          = 2,
   gxOmitPatternUYShift          = 0
   };

Constant descriptions

gxOmitPatternAttributesShift

The bit shift required to isolate the compression bits for the attributes field descriptor.

gxOmitPatternShapeShift

The bit shift required to isolate the compression bits for the pattern field descriptor.

gxOmitPatternUXShift

The bit shift required to isolate the compression bits for the ux field descriptor.

gxOmitPatternUYShift

The bit shift required to isolate the compression bits for the uy field descriptor.

The gxOmitPatternMask2 enumeration defines which bits in a second omit byte correspond to the data compression opcode for additional field descriptors in the gxPatternRecord structure. The sequence of data is also continued. The omit byte and its related data sequence is given in the section "Pattern Data" beginning on page 7-38.

enum gxOmitPatternMask2 {
   gxOmitPatternVXMask = 0xC0,
   gxOmitPatternVYMask = 0x30
};

Constant descriptions

gxOmitPatternVXMask

The mask used to select the data compression bits for the u.x field descriptor.

gxOmitPatternVYMask

The mask to select the data compression bits for the u.y field descriptor.

Once one of the gxOmitPatternMask2 enumeration masks has been used to select a data compression opcode for one of the field descriptors in the gxPatternRecord structure, the corresponding bit shift from the gxOmitPatternShift2 enumeration can be applied to the selected bits. The selected bits must be moved to the right by the indicated number of bits to isolate the data compression opcode so that it can be compared to other values.

enum gxOmitPatternShift2 {
   gxOmitPatternVXShift= 6,
   gxOmitPatternVYShift= 4
};

Constant descriptions

gxOmitPatternVXShift

The bit shift required to isolate the compression bits for the u.x field descriptor.

gxOmitPatternVYShift

The bit shift required to isolate the compression bits for the u.y field descriptor.