Custom Atoms

The author of a QuickTime VR movie may choose to add custom atoms to either the VR world or node information atom containers. Those atoms can be extracted within an application to provide additional information that the application may use.

Information that pertains to the entire scene might be stored in a custom atom within the VR world atom container. Node-specific information could be stored in the individual node information atom containers or as sibling atoms to the node location atoms within the VR world.

Custom hot spot atoms should be stored as siblings to the hot spot information atoms in the node information atom container. Generally, its atom type is the same as the custom hot spot type. You can set up an intercept procedure in your application in order to process clicks on the custom hot spots.

If you use custom atoms, you should install your hot spot intercept procedure when you open the movie. Listing 4-2 is an example of such an intercept procedure.

Listing 2 Typical hot spot intercept procedure



 
QTVRInterceptProc MyProc = NewQTVRInterceptProc (MyHotSpot);

QTVRInstallInterceptProc (qtvr, kQTVRTriggerHotSpotSelector, myProc, 0, 0);



pascal void MyHotSpot (QTVRInstance qtvr, QTVRInterceptPtr qtvrMsg, 

                        SInt32 refCon, Boolean *cancel)

{

    UInt32 hotSpotID = (UInt32) qtvrMsg->parameter[0];

    QTAtomContainer nodeInfo =

            (QTAtomContainer) qtvrMsg->parameter[1];

    QTAtom hotSpotAtom = (QTAtom) qtvrMsg->parameter[2];

    OSType hotSpotType;

    CustomData myCustomData;

    QTAtom myAtom;

    

    QTVRGetHotSpotType (qtvr, hotSpotID, &hotSpotType);

    if (hotSpotType != kMyAtomType) return;

        

    // It's our type of hot spot - don't let anyone else handle it

    *cancel = true;

    

    // Find our custom atom

    myAtom = QTFindChildByID (nodeInfo, hotSpotAtom, kMyAtomType, 1, nil);

    if (myAtom != 0) {

        OSErr err;

        // Copy the custom data into our structure

        err = QTCopyAtomDataToPtr (nodeInfo, myAtom, false, 

                        sizeof(CustomData), &myCustomData, nil);

        if (err == noErr)

            // Do something with it

            DoMyHotSpotStuff (hotSpotID, &myCustomData);

    }

}

Your intercept procedure is called for clicks on any hot spot. You should check to see if it is your type of hot spot and if so, extract the custom hot spot atom and do whatever is appropriate for your hot spot type (DoMyHotSpotStuff ).

When you no longer need the intercept procedure you should call QTVRInstallInterceptProc again with the same selector and a nil procedure pointer and then call DisposeRoutineDescriptor on myProc .

Apple reserves all hot spot and atom types with lowercase letters. Your custom hot spot type should contain all uppercase letters.

| Previous | Chapter Contents | Chapter Top |