Legacy Document

Inside Macintosh: Imaging With QuickDraw /

Chapter 4 - Color QuickDraw / Color QuickDraw Reference

Color QuickDraw Routines / Creating and Disposing of Color Tables

GetCTable

To get a color table stored in a 'clut' resource, use the GetCTable function.

FUNCTION GetCTable (ctID: Integer): CTabHandle;

ctID

The resource ID of a 'clut' resource.

DESCRIPTION

For the color table defined in the 'clut' resource that you specify in the ctID parameter, the GetCTable function returns a handle to a ColorTable record. If the 'clut' resource with that ID is not found, GetCTable returns NIL.

If you place this handle in the pmTable field of a PixMap record, you should first use the DisposeCTable procedure to dispose of the handle already there.

If you modify a ColorTable record, you should invalidate it by changing its ctSeed field. An easy way to do this is with the CTabChanged procedure, described on page 4-88.

The GetCTable function recognizes a number of standard 'clut' resource IDs. You can obtain the default grayscale color table for a given pixel depth by calling GetCTable, adding 32 (decimal) to the pixel depth, and passing this value in the ctID parameter, as shown in Table 4-5.

Table 4-5 The default color tables for grayscale graphics devices

Pixel depth	Resource ID	Color table composition
1	33	Black, white
2	34	Black, 33% gray, 66% gray, white
4	36	Black, 14 shades of gray, white
8	40	Black, 254 shades of gray, white

For full color, you can obtain the default color tables by adding 64 to the pixel depth and passing this in the ctID parameter, as shown in Table 4-6. These default color tables are illustrated in Plate 1 at the front of this book.

Table 4-6 The default color tables for color graphics devices

Pixel depth	Resource ID	Color table composition
2	66	Black, 50% gray, highlight color, white
4	68	Black, 14 colors including the highlight color, white
8	72	Black, 254 colors including the highlight color, white

SPECIAL CONSIDERATIONS

The GetCTable function may move or purge memory blocks in the application heap. Your application should not call this function at interrupt time.

SEE ALSO

The 'clut' resource is described on page 4-94.