[Alephmodular-devel] Macintosh oddity: GetCTable(8)?

[Br'fin <br...@ma...>]

I was poking through AlephModular while trying to rehandle how cluts 
were used. And I stumbled upon the usage of GetCTable(8). Which, upon 
checking PB's docs for GetCTable seemed wrong. And so I checked in 
AlephOne and found the same issue (It dates back to the Marathon2 code 
originally)

Both things call GetCTable with an argument of 8 ... it seems like the 
correct argument should be 72. I don't know of any tech notes that 
would say that 8 should also work for a 256 color system clut.

Can anyone confirm or deny that this is some kind of 256 color problem?

-Jeremy Parsons


 From AlephOne: FileHandler.h

	void GetSystemColorTable()
		{Unload(); RsrcHandle = Handle(GetCTable(8));}


 From PB's reference docs:
GetCTable

Obtains a color table stored in a 'clut' resource.

CTabHandle GetCTable (
     SInt16 ctID
);

Parameter descriptions

ctID

The resource ID of a 'clut' resource.

function result

A handle to the color table. If the 'clut' resource with that ID is not 
found, GetCTable returns NULL.Before you place this handle in the 
pmTable field of a PixMap structure, first use the DisposeCTable 
function to dispose of the handle already there.

Discussion

Before you modify a ColorTable structure, change its ctSeed field to 
invalidate it. To do this, use the CTabChanged function.

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 these values in the ctID parameter:

* A pixel depth of 1

Pass a resource ID of 33. Color table composition: black, white.

* A pixel depth of 2

Pass a resource ID of 34. Color table composition: black, 33% gray, 66% 
gray, white.

* A pixel depth of 3

Pass a resource ID of 35. Color table composition: black, 14 shades of 
gray, white.

* A pixel depth of 4

Pass a resource ID of 36. Color table composition: black, 254 shades of 
gray, white.

For full color, obtain the default color tables by adding 64 to the 
pixel depth and passing these values in the ctID parameter:

* A pixel depth of 2

Pass a resource ID of 66. Color table composition: black, 50% gray, 
highlight color, white.

* A pixel depth of 4

Pass a resource ID of 68. Color table composition: black, 14 colors 
including the highlight color, white.

* A pixel depth of 8

Pass a resource ID of 72. Color table composition: black, 254 colors 
including the highlight color, white.

Availability

Supported in Carbon. Available in CarbonLib 1.0 and later when running 
Mac OS 8.1 or later. Available in Mac OS X 10.0 and later.

Special Considerations

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