Inside Macintosh: QuickDraw GX Environment and Utilities /

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

Opcode Constants and Data Types

Data Type Opcode Byte

Bits 6 and 7 of the data type opcode byte are the compression type opcode. The compression of the data to follow is given by the gxTwoBitCompressionValues enumeration in Table 7-3. The gxCompressionMask constant, binary 11, masks the constant defined by the gxTwoBitCompressionValue enumeration.

#define gxCompressionMask  0x03

The gxCompressionShift constant defines the number of bits to be shifted to the right so that the masked value of the compression type opcode can be compared to other values.

#define gxCompressionShift 6

Bits 0 through 5 of the data type opcode byte are the data type opcode. These opcodes describe the data that follows in the stream. The gxObjectTypeMask constant, binary 111111, masks bits 0 through 5 of the data type opcode byte to select the data type opcode. No shift is required to compare the data type opcode with other values.

#define gxObjectTypeMask   0x3F