QuickTime 3 Reference

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Parameter Alternate Data Type ( kParameterAlternateDataType , `altl' )

This atom defines an alternative data type for the parameter. The alternative is the data type of the value stored in the parameter, if that data type is supported by the system your application is running on. If the system does not support this data type, the parameter will store a value whose data type is specified in the Parameter Data Type atom.

For example, if the Parameter Alternate Data Type is kParameterTypeDataColorValue , the parameter holds a value of type CMColor ; however, this type is only supported by systems that have the ColorSync extension loaded. On systems that do not have ColorSync, the Parameter Data Type will be used instead.

This atom's data is stored in a ParameterAlternateDataType data structure, which in turn relies on the ParameterAlternateDataEntry data structure.

typedef struct
{
    OSType      dataType;       // The type of the data
    QTAtomType  alternateAtom;  // The atom to use for alternate data
} ParameterAlternateDataEntry;

typedef struct
{
    long                        alternateCount;
    ParameterAlternateDataEntry alternates[];
} ParameterAlternateDataType;
dataType
This field in the ParameterAlternateDataEntry structure can take one of the following values:
kParameterTypeDataColorValue - CM Color data
 
kParameterTypeDataCubic - cubic bezier(s)
 
kParameterTypeDataNURB - nurb(s)
 

The Parameter Alternate Data Type atom is optional.

© 1997 Apple Computer, Inc.

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