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Inside Macintosh: QuickDraw GX Environment and Utilities /

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

Data Type Opcode Byte

A data type opcode byte always follows the record size. This byte contains both a compression type opcode and a data type opcode. Figure 7-5 shows the format of the data type opcode byte.

Figure 7-5 The format of the data type opcode byte

Compression Type Opcode

Bits 6 and 7 of the data type opcode byte contain the compression type opcode. This opcode specifies the type of compression used for the data that follows. The 2-bit compression opcode constants from the gxTwoBitCompressionValues enumeration specifies whether the next data are longs, words, bytes, or that no data follows. Table 7-2 lists the compression type opcode values.

Table 7-2 Compression values

Value	Description
0x00	No compression has been applied. The data that follows are long words.
0x40	Word compression has been applied. The data that follows are words.
0x80	Byte compression has been applied. The data that follows are bytes.
0xC0	Omit compression. No data follows.

The gxTwoBitCompressionValues enumeration is also used to interpret the compression in the omit byte. For additional information about the interpretation of omit bytes, see the section "Omit Byte Masks and Omit Byte Shifts" beginning on page 7-22.

The relationship of the operation opcode, record size, compression type opcode, data type opcode, and optional data for a header or object is shown in Figure 7-6.

Figure 7-6 Relationship of stream format components

The appearance or absence of data after the data type opcode byte depends upon the values that appear in the operation opcode byte and the data type opcode byte.

If the gxNewObjectOpcode constant appears in the operation opcode byte, a new object follows. The new object copies the default values into the newly created object. The default values may have been changed by the last object created of this type. If the last object and the current object are equal, then the new object requires no additional data for its definition. In this case, the stream following the new opcode byte contains only the compression and data type opcode byte with compression set to no compression.

If the gxSetDataOpcode constant appears in the operation opcode byte, the record length is greater than 1 byte and object-specific data follows.

The gxSetDefaultOpcode constant appears only after the current object type has been defined. If the gxSetDefaultOpcode constant appears in the operation opcode byte, the data type opcode contains the gxStyleTypeOpcode, gxInkTypeOpcode, or gxTransformTypeOpcode constant. The compression type opcode defines the compression of the data of the object reference number that follows. This previously defined object becomes the default styles, ink, or transform for the shapes created subsequently.

The sequence of the object-specific data that follows the data type opcode byte is described in the next section. Subsections are provided for the header, shape data, style, ink, transform, color profile, color set, tag, bit image, font name, and trailer objects.

Data Type Opcode

Bits 0 through 5 of the data type opcode byte contain the data type opcode. This opcode specifies the type of data that follows. The type of data that follows depends upon the current value of the operation opcode. If the operation opcode is gxNewObjectOpcode, the data type opcode describes a new object. These data type opcodes are described in the next section. If the operation opcode is gxSetDataOpcode, the data type opcode, specifies how the current object will be modified. These data type opcodes are described in the sections "Data Type Opcodes to Modify a Shape Object" beginning on page 7-17, "Data Type Opcodes to Modify a Color Set Object" beginning on page 7-20, "Data Type Opcodes to Modify a Color Profile Object" beginning on page 7-21, and "Data Type Opcodes to Modify a Transform Object" beginning on page 7-21.

Data Type Opcodes for a New Object

When the current operation opcode is the gxNewObjectOpcode constant, bits 0 through 5 of the data type opcode byte specify the data type opcode for the new object. Data type opcode constants for header, style, ink, transform, color profile, color set, tag type, bit image, font name, and trailer are defined in the gxGraphicsNewOpcode enumeration. Data type opcode constants for empty, point, line, curve, rectangle, polygon, path, bitmap, text, glyph, layout, full, and picture are defined in the gxShapeTypes enumeration. Table 7-3 summarizes all of the data type opcodes for a new object.

Table 7-3 Data type opcodes for a new object

Constant	Value	Description
gxHeaderTypeOpcode	0x00	The data that follows is the header.
gxEmptyType	0x01	The data that follows describes an empty shape object. See the GXNewShape(gxEmptyType) function.
gxPointType	0x02	The data that follows describes a point object. See the GXNewPoint function.
gxLineType	0x03	The data that follows describes a line object. See the GXNewLine function.
gxCurveType	0x04	The data that follows describes a curve object. See the GXNewCurve function.
gxRectangleType	0x05	The data that follows describes a rectangle object. See the GXNewRectangle function.
gxPolygonType	0x06	The data that follows describes a polygon object. See the GXNewPolygons function.
gxPathType	0x07	The data that follows describes a path object. See the GXNewPaths function.
gxBitmapType	0x08	The data that follows describes a bitmap object. See the GXNewBitmap function.
gxTextType	0x09	The data that follows describes a text object. See the GXNewText function.
gxGlyphType	0x10	The data that follows describes a glyph object. See the GXNewGlyph function.
gxLayoutType	0x11	The data that follows describes a layout object. See the GXNewLayout function.
gxFullType	0x12	The data that follows describes a full shape object. See the GXNewShape(gxFullType) function.
gxPictureType	0x13	The data that follows describes a picture object. See the GXNewPicture function.
gxStyleTypeOpcode	0x28	The data that follows describes a style object. See the GXNewStyle function.
gxInkTypeOpcode	0x29	The data that follows describes an ink object. See the GXNewInk function.
gxTransformTypeOpcode	0x2A	The data that follows describes a transform object. See the GXNewTransform function.
gxColorProfileOpcode	0x2B	The data that follows describes a color profile object. See the GXNewColorProfile function.
gxColorSetOpcode	0x2C	The data that follows describes a color set object. See the GXNewColorSet function.
gxTagTypeOpcode	0x2D	The data that follows describes a tag object. See the GXNewTag function.
gxBitImageOpcode	0x2E	The data that follows describes a bit image, the bits pointed to by a bitmap.
gxFontNameTypeOpcode	0x2F	The data that follows describes a font name. See the GXNewFont function.
gxTrailerTypeOpcode	0x3F	This opcode indicates the end of a data stream.

The omitted numbers are reserved by Apple Computer, Inc. for future use. You should extend the stream format by using tag objects to encapsulate custom data. Tags are described in the "Tag Objects" in Inside Macintosh:QuickDraw GX Objects.

Data Type Opcodes to Modify a Shape Object

When the current object is a shape object and the current operation opcode is the gxSetDataOpcode constant, bits 0 through 5 of the data type opcode byte specify the data type opcode for the shape object to be modified. Data type opcode constants for attributes, tag, ink, and fill are defined in the gxShapeDataOpcode enumeration.
Table 7-4 summarizes all of the data type opcodes used to modify a shape object.

Table 7-4 Data type opcodes to modify a shape object

Constant	Value	Description
gxShapeAttributesOpcode	0x00	The attributes data that follows is added to the current shape object. See the GXSetShapeAttributes function.
gxTagOpcode	0x01	The tag data that follows is added to the current shape object. See the GXSetShapeTags function.
gxFillOpcode	0x02	The fill data that follows is added to the current shape object. See the GXSetShapeFill function.

Data Type Opcodes to Modify a Style Object

When the current object is a style object and the current operation opcode is the gxSetDataOpcode constant, bits 0 through 5 of the data type opcode byte specify the data type opcode for the style object to be modified. Data type opcode constants for attributes, tag, curve error, pen, join, dash, caps, pattern, text attributes, text size, font, text face, platform, font variations, run controls, run priority justification override, run glyph justification overrides, run glyph substitutions, run features, run kerning adjustments, and justification are defined in the gxStyleDataOpcode enumeration. Table 7-5 summarizes all of the data type opcodes used to modify a style object.

Table 7-5 Data type opcodes to modify a style object

Constant	Value	Description
gxStyleAttributesOpcode	0x00	The attributes data that follows is added to the current shape object. See the GXSetStyleAttributes function.
gxStyleTagOpcode	0x01	The tag data that follows is added to the current shape object. See the GXSetStyleTags function.
gxStyleCurveErrorOpcode	0x02	The curve error data that follows is added to the current style object. See the GXSetStyleCurveError function.
gxStylePenOpcode	0x03	The pen data that follows is added to the current style object. See the GXSetStylePen function.
gxStyleJoinOpcode	0x04	The join data that follows is added to the current style object. See the GXSetStyleJoin function.
gxStyleDashOpcode	0x05	The dash data that follows is added to the current style object. See the GXSetStyleDash function.
gxStyleCapsOpcode	0x06	The caps data that follows is added to the current style object. See the GXSetStyleCaps function.
gxStylePatternOpcode	0x07	The pattern data that follows is added to the current style object. See the GXSetStylePattern function.
gxStyleTextAttributesOpcode	0x08	The text attributes data that follows is added to the current style object. See the GXSetStyleTextAttributes function.
gxStyleTextSizeOpcode	0x09	The text size data that follows is added to the current style object. See the GXSetStyleTextSize function.
gxStyleFontOpcode	0x0A	The font data that follows is added to the current style object. See the GXSetStyleFont function.
gxStyleTextFaceOpcode	0x0B	The text face data that follows is added to the current style object. See the GXSetStyleFace function.
gxStylePlatformOpcode	0x0C	The platform data that follows is added to the current style object. See the GXSetStyleEncoding function.
gxStyleFontVariationsOpcode	0x0D	The font variations data that follows is added to the current style object. See the GXSetStyleFontVariations function.
gxStyleRunControlsOpcode	0x0E	The run controls data that follows is added to the current style object. See the GXSetStyleRunControls function.
gxStyleRunPriorityJustOverrideOpcode	0x1F	The run priority justification override data that follows is added to the current style object. See the GXSetStyleRunPriorityJust Override function.
gxStyleRunGlyphJustOverridesOpcode	0x10	The run glyph justification overrides data that follows is added to the current style object. See the GXStyleRunGlyphJust Overrides function.
gxStyleRunGlyphSubstitutionsOpcode	0x11	The run glyph substitutions data that follows is added to the current style object. See the GXStyleRunGlyphSubstitutions function.
gxStyleRunFeaturesOpcode	0x12	The run features data that follows is added to the current style object. See the GXStyleRunFeatures function.
gxStyleRunKerningAdjustmentsOpcode	0x13	The run kerning adjustments data that follows is added to the current style object. See the GXStyleRunKerning Adjustments function.
gxStyleJustificationOpcode	0x14	The justification data that follows is added to the current style object. See the GXStyleJustification function.

Data Type Opcodes to Modify an Ink Object

When the current object is an ink object and the current operation opcode is the gxSetDataOpcode constant, bits 0 through 5 of the data type opcode byte specify the data type opcode for the ink object to be modified. Data type opcode constants for attributes, tag, color, and transfer mode are defined in the gxInkDataOpcode enumeration. Table 7-6 summarizes all of the data type opcodes used to modify an ink object.

Table 7-6 Data type opcodes to modify an ink object

Constant	Value	Description
gxInkAttributesOpcode	0x00	The attributes data that follows is added to the current ink object. See the GXSetInkAttributes function.
gxInkTagOpcode	0x01	The tag data that follows is added to the current ink object. See the GXSetInkTags function.
gxInkColorOpcode	0x02	The ink color data that follows is added to the current ink object. See the GXSetInkColor function.
gxInkTransferModeOpcode	0x03	The ink transfer mode data that follows is added to the current ink object. See the GXSetInkTransfer function.

Data Type Opcodes to Modify a Color Set Object

When the current object is a color set object and the current operation opcode is the gxSetDataOpcode constant, bits 0 through 5 of the data type opcode byte specify the data type opcode for the color set object to be modified. A data type opcode constant for tag is defined in the gxColorSetDataOpcode enumeration. The constant 0 is reserved for future use. Table 7-7 summarizes all of the data type opcodes used to modify a color set object.

Table 7-7 Data type opcodes to modify a color set object

Constant	Value	Description
gxColorSetReservedOpcode	0x00	This constant is reserved for future assignment.
gxColorSetTagOpcode	0x01	The tag data that follows is added to the current color set object. See the GXSetColorSetTags function.

Data Type Opcodes to Modify a Color Profile Object

When the current object is a color profile object and the current operation opcode is the gxSetDataOpcode constant, bits 0 through 5 of the data type opcode byte specify the data type opcode for the color profile object to be modified. A data type opcode constant for tag is defined in the gxProfileDataOpcode enumeration. The constant 0 is reserved for future use. Table 7-8 summarizes the data type opcodes used to modify a color profile object.

Table 7-8 Data type opcodes to modify a color profile object

Constant	Value	Description
gxColorProfileReservedOpcode	0x00	This constant is reserved for future assignment.
gxColorProfileTagOpcode	0x01	The tag data that follows is added to the current color profile object. See the GXSetColorProfileTags function.

Data Type Opcodes to Modify a Transform Object

When the current object is a transform object and the current operation opcode is the gxSetDataOpcode constant, bits 0 through 5 of the data type opcode byte specify the data type opcode for the transform object to be modified. A data type opcode constant for tag is defined in the gxTransformDataOpcode enumeration. The constant 0 is reserved for future use. Table 7-9 summarizes the data type opcodes used to modify a transform object.

Table 7-9 Data type opcodes to modify a transform object

Constant	Value	Description
gxTransformReservedOpcode	0x00	This constant is reserved for future assignment.
gxTransformTagOpcode	0x01	The tag data that follows is added to the current transform object. See the GXSetTransformTags function.
gxTransformClipOpcode	0x02	The tag data that follows is added to the current transform object. See the GXSetTransformClip function.
gxTransformMappingOpcode	0x03	The tag data that follows is added to the current transform object. See the GXSetTransformMapping function.
gxTransformPartMaskOpcode	0x04	The tag data that follows is added to the current transform object. See the description of the gxShapePart mask parameter to the GXSetTransformHitTest function.
gxTransformToleranceOpcode	0x05	The tag data that follows is added to the current transform object. See the description of the Fixed tolerance parameter to the GXSetTransformHitTest function.