Inside Macintosh: Imaging With QuickDraw /

Appendix A - Picture Opcodes

Picture Opcode Data Types

The picture opcodes use the data types that are summarized in Table A-1.

Table A-1 Data types for picture opcodes (Continued)

Data type	Size
-128..127	1 byte (signed)
0..255	1 byte
Fixed	4 bytes
Integer	2 bytes
Long	4 bytes
Mode	2 bytes
Opcode	2 bytes
Pattern	8 bytes
Point	4 bytes
Poly	10+ bytes
Rect	8 bytes (top, left, bottom, right: integer)
Rgn	10+ bytes
RowBytes	2 bytes (always an even quantity)

In addition, some picture opcode types, such as BkPixPat, may use the PixMap, ColorTable, and PixData data types, which makes the length of these opcodes quite variable. The PixMap record and ColorTable record are described in the chapter "Color QuickDraw" in this book. The following pseudocode describes the PixData data type:

PixData: {pseudocode describing the PixData data type}
IF rowBytes < 8 THEN 
   data is unpacked; 
   data size = rowBytes*(bounds.bottom-bounds.top);
IF rowBytes >= 8 THEN 
   data is packed;
   image contains (bounds.bottom-bounds.top) packed scanlines;



   packed scanlines are produced by the PackBits routine;
   each scanline consists of [byteCount] [data];
   IF rowBytes > 250 THEN 
      byteCount is a word;
   ELSE 
      byteCount is a byte.
END;