QuickTime 4 Reference

Removing Atoms From an Atom Container

To remove atoms from an atom container, you can use the QTRemoveAtom and QTRemoveChildren functions. The QTRemoveAtom function removes an atom and its children, if any, from a container. The QTRemoveChildren function removes an atom's children from a container, but does not remove the atom itself. You can also use QTRemoveChildren to remove all the atoms in an atom container. To do so, you should pass the constant kParentAtomIsContainer for the atom parameter.

The code sample shown in Listing 11 adds override samples to a sprite track to animate the sprites in the sprite track. The sample and spriteData variables are atom containers. The spriteData atom container contains atoms that describe a single sprite. The sample atom container contains atoms that describes an override sample.

Each iteration of the for loop calls QTRemoveChildren to remove all atoms from both the sample and the spriteData containers. The sample code updates the index of the image to be used for the sprite and the sprite's location and calls SetSpriteData ( Listing 8 ), which adds the appropriate atoms to the spriteData atom container. Then, the sample code calls AddSpriteToSample ( Listing 9 ) to add the spriteData atom container to the sample atom container. Finally, when all the sprites have been updated, the sample code calls AddSpriteSampleToMedia to add the override sample to the sprite track.

Listing 11 Removing atoms from a container



 
QTAtomContainer sample, spriteData;



// ...

// add the sprite key sample

// ...



// add override samples to make the sprites spin and move

for (i = 1; i <= kNumOverrideSamples; i++) 

{

    QTRemoveChildren (sample, kParentAtomIsContainer);

    QTRemoveChildren (spriteData, kParentAtomIsContainer);

    

    // ...

    // update the sprite:

    // - update the imageIndex

    // - update the location

    // ...



    // add atoms to spriteData atom container

    SetSpriteData (spriteData, &location, nil, nil, &imageIndex);



    // add the spriteData atom container to sample

    err = AddSpriteToSample (sample, spriteData, 2);



    // ...

    // update other sprites

    // ...



    // add the sample to the media

    err = AddSpriteSampleToMedia (newMedia, sample,

        kSpriteMediaFrameDuration, false);

}