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GetGammaInfoList (csCode = 20)

The GetGammaInfoList routine is optional. Clients wishing to find a graphics card's available gamma tables formerly accessed the Slot Manager data structures. PCI graphics drivers must return this information directly.

In the future, gamma tables will be part of the display's domain, not the graphics driver's domain. In the meantime, graphics drivers must still provide support for them by responding to the GetGammaInfoList and RetrieveGammaTable calls. The GetGammaInfoList routine iterates over the gamma tables supported by the driver for the attached display.



 
OSErr = Status(theDeviceRefNum, cscGetGammaInfoList, &theVDGammaListRec);

--> csPreviousGammaTableID: ID of the previous gamma table
<-- csGammaTableID: ID of the gamma table following csPreviousDisplayModeID
<-- csGammaTableSize: Size of the gamma table in bytes
<-- csGammaTableName: Gamma table name (C string)

The csGammaTableName parameter is a C string with a maximum of 31 characters. The driver needs to copy the name from its storage to the storage passed in by the caller. It can use CStrCopy. The caller uses csGammaTableSize to allocate storage to read the entire structure, using the RetrieveGammaTable routine.

Observe these cautions:

A client will pass a csPreviousGammaTableID of kGammaTableIDFindFirst to get the first gamma table ID. The driver should return this value in the csGammaTableID field.
If the last gamma table ID is passed in the csPreviousGammaTableID field, the driver should put a kGammaTableIDNoMoreTables in the csGammaTableID field and return noErr .
If an invalid gamma table ID is passed in the csPreviousGammaTableID field, the driver should return paramErr and should not modify the data structure.
A client can pass csPreviousGammaTableID with a value of kGammaTableIDSpecific . This tells the driver that the csGammaTableID contains the ID of the table that the client wants information about. This is a way to bypass iteration through all the tables when the caller already knows the GammaTableID .
Although the GetGammaInfoList call appears to perform its iteration operations similarly to the GetNextResolution call, there is an important difference. GetGammaInfoList only returns information for gamma tables that are applicable to the attached display; GetNextResolution returns the information regardless of what display is connected.