QuickTime 4 Reference

Creating New Atoms

You can use the QTInsertChild function to create new atoms and insert them in a QT atom container. The QTInsertChild function creates a new child atom for a parent atom. The caller specifies an atom type and atom ID for the new atom. If you specify a value of 0 for the atom ID, QTInsertChild assigns a unique ID to the atom.

QTInsertChild inserts the atom in the parent's child list at the index specified by the index parameter; any existing atoms at the same index or greater are moved toward the end of the child list. If you specify a value of 0 for the index parameter, QTInsertChild inserts the atom at the end of the child list.

The code sample in Listing 5 creates a new QT atom container and calls QTInsertChild to add an atom. The resulting QT atom container is shown in Figure 3 . The offset value 10 is returned in the firstAtom parameter.

Listing 5 Creating a new QT atom container and calling QTInsertChild to add an atom.



 
QTAtom firstAtom;

QTAtomContainer container;

OSErr err

err = QTNewAtomContainer (&container);

if (!err)

    err = QTInsertChild (container, kParentAtomIsContainer, 'abcd',

        1000, 1, 0, nil, &firstAtom);

Figure 3 QT atom container after inserting an atom

The following code sample calls QTInsertChild to create a second child atom. Because a value of 1 is specified for the index parameter, the second atom is inserted in front of the first atom in the child list; the index of the first atom is changed to 2. The resulting QT atom container is shown in Figure 4 .



 
QTAtom secondAtom;



FailOSErr (QTInsertChild (container, kParentAtomIsContainer, 'abcd',

    2000, 1, 0, nil, &secondAtom));

Figure 4 QT atom container after inserting a second atom

You can call the QTFindChildByID function to retrieve the changed offset of the first atom that was inserted, as shown in the following example. In this example, the QTFindChildByID function returns an offset of 20.



 
firstAtom = QTFindChildByID (container, kParentAtomIsContainer, 'abcd',

    1000, nil);

Listing 6 shows how the QTInsertChild function inserts a leaf atom into the atom container sprite . The new leaf atom contains a sprite image index as its data.

Listing 6 Inserting a child atom



 
if ((propertyAtom = QTFindChildByIndex (sprite, kParentAtomIsContainer,

    kSpritePropertyImageIndex, 1, nil)) == 0)



    FailOSErr (QTInsertChild (sprite, kParentAtomIsContainer,

        kSpritePropertyImageIndex, 1, 1, sizeof(short),&imageIndex,

        nil));