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Chapter 2 - Movie Toolbox / Movie Toolbox Reference

Time Base Functions / Time Base Callback Functions

CallMeWhen

You schedule a callback event by calling the CallMeWhen function. You can call this function from your callback function.

pascal OSErr CallMeWhen (QTCallBack cb, 
                           QTCallBackProc callBackProc, 
                           long refcon, long param1, 
                           long param2, long param3);

cb

Specifies the callback event for the operation. You obtain this identifier from the NewCallBack function, which is described in the previous section.

callBackProc

Points to your callback function.

Your callback function must have the following form:

            pascal void MyCallBackProc (QTCallBack cb, 
                                          long refcon);

See "Callback Event Functions" on page 2-342 for details.

refcon

Contains a reference constant value for your callback function.

param1

Contains scheduling information. The Movie Toolbox interprets this parameter based on the value of the cbType parameter to the NewCallBack function, described in the previous section.

If cbType is set to callBackAtTime, the param1 parameter contains flags indicating when to invoke your callback function for this callback event. The following values are defined (be sure to set unused flags to 0):

triggerTimeFwd

Indicates that your callback function should be called at the time specified by param2 only when time is moving forward (positive rate). The value of this flag is 0x0001.

triggerTimeBwd

Indicates that your callback function should be called at the time specified by param2 only when time is moving backward (negative rate). The value of this flag is 0x0002.

triggerTimeEither

Indicates that your callback function should be called at the time specified by param2 without regard to direction, but the rate must be nonzero. The value of this flag is 0x0003.

If the cbType parameter is set to callBackAtRate, param1 contains flags indicating when to invoke your callback function for this event. The following values are defined (be sure to set unused flags to 0):

triggerRateChange

Indicates that your callback function should be called whenever the rate changes. The value of this flag is 0x0000.

triggerRateLT

Indicates that your callback function should be called when the rate changes to a value less than that specified by param2. The value of this flag is 0x0004.

triggerRateGT

Indicates that your callback function should be called when the rate changes to a value greater than that specified by param2. The value of this flag is 0x0008.

triggerRateEqual

Indicates that your callback function should be called when the rate changes to a value equal to that specified by param2. The value of this flag is 0x0010.

triggerRateLTE

Indicates that your callback function should be called when the rate changes to a value that is less than or equal to that specified by param2. The value of this flag is 0x0014.

triggerRateGTE

Indicates that your callback function should be called when the rate changes to a value that is less than or equal to that specified by param2. The value of this flag is 0x0018.

triggerRateNotEqual

Indicates that your callback function should be called when the rate changes to a value that is not equal to that specified by param2. The value of this flag is 0x001C.

param2

Contains scheduling information. The Movie Toolbox interprets this parameter based on the value of the cbType parameter to the NewCallBack function, described in the previous section.

If cbType is set to callBackAtTime, the param2 parameter contains the time value at which your callback function is to be invoked for this event. The param1 parameter contains flags affecting when the Movie Toolbox calls your function.

If cbType is set to callBackAtRate, the param2 parameter contains the rate value at which your callback function is to be invoked for this event. The param1 parameter contains flags affecting when the Movie Toolbox calls your function.

param3

Contains the time scale in which to interpret the time value that is stored in param3 if cbType is set to callBackAtTime.

ERROR CODES

None