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Inside Macintosh: QuickDraw GX Environment and Utilities /

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

Shape Object Omit Byte Constants and Data Types

Path Shape Omit Byte Masks and Shifts

The gxOmitPathMask enumeration defines which bits in an omit byte correspond to the data compression opcode for the field descriptors in the gxPaths structure. The sequence of data is also defined. The omit byte and its related data sequence is given in the section "Path Shape Data" beginning on page 7-31.

enum gxOmitPathMask {
   gxOmitPathPositionXMask = 0xC0,
   gxOmitPathPositionYMask = 0x30,
   gxOmitPathDeltaXMask    = 0x0C,
   gxOmitPathDeltaYMask    = 0x03
};

Constant descriptions

gxOmitPathPositionXMask

The mask used to select the data compression bits for the vector[0].x field descriptor.

gxOmitPathPositionYMask

The mask used to select the data compression bits for the vector[0].y field descriptor.

gxOmitPathDeltaXMask

The mask used to select the data compression bits for the vector[n].x field descriptor where n is greater than zero, represented as a delta from the previous value.

gxOmitPathDeltaYMask

The mask used to select the data compression bits for the vector[n].y field descriptor where n is greater than zero, represented as a delta from the previous value.

Once one of the gxOmitPathMask enumeration masks has been used to select a data compression opcode for a field descriptor in the gxPaths?? structure, the corresponding bit shift from the gxOmitPathShift 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 gxOmitPathShift {
   gxOmitPathPositionXShift   = 6,
   gxOmitPathPositionYShift   = 4,
   gxOmitPathDeltaXShift      = 2,
   gxOmitPathDeltaYShift      = 0
};

Constant descriptions

gxOmitPathPositionXShift

The bit shift required to isolate the compression bits for thevector[0].x field descriptor.

gxOmitPathPositionYShift

The bit shift required to isolate the compression bits for thevector[0].y field descriptor.

gxOmitPathDeltaXShift

The bit shift required to isolate the compression bits for the vector[n].x field descriptor where n is greater than zero, represented as a delta from the previous value.

gxOmitPathDeltaYShift

The bit shift required to isolate the compression bits for the vector[n].y field descriptor where n is greater than zero, represented as a delta from the previous value.