Wired Movies and Sprites

Getting Sprite Data From a Modifier Track

The sample program AddReferenceTrack.c illustrates how you can modify a movie to use a modifier track for a sprite's image data. The sample program prompts the user for a movie that contains a single sprite track. Then, it adds a track from a second movie to the original movie as a modifier track. The modifier track overrides the image data for a selected image index.

Listing 3-13 shows the first part of the main function of the sample program. It performs the following tasks:

It loads the movie containing the sprite track.
It calls GetMovieTrackCount to determine the total number of tracks in the sprite track movie.
It loads the movie containing the modifier track (movieB ).

Listing 13 Loading the movies



 
OSErr               err;

short               movieResID = 0, resFref, resID = 0, resRefNum;

StandardFileReply   reply;

SFTypeList          types;

Movie               m;

FSSpec              fss;

Movie               movieB;

long                origTrackCount;



// prompt for a movie containing a sprite track and load it

types[0] = MovieFileType;

StandardGetFilePreview (nil, 1, types, &reply);

if (!reply.sfGood) return;



err = OpenMovieFile (&reply.sfFile, &resFref, fsRdPerm);

if (err) return;



err = NewMovieFromFile (&m, resFref, &movieResID, (StringPtr)nil,

    newMovieActive, ni);

if (err) return;



CloseMovieFile (resFref);



// get the number of tracks

origTrackCount = GetMovieTrackCount (m);



// load the movie to be used as a modifier track

FSMakeFSSpec (reply.sfFile.vRefNum, reply.sfFile.parID, "\pAdd Me",

    &fss);



err = OpenMovieFile (&fss, &resFref, fsRdPerm);

if (err) return;



err = NewMovieFromFile (&movieB, resFref, &resID, (StringPtr)nil, 0,

    nil);

if (err) return;



CloseMovieFile (resFref);

Once the two movies have been loaded, the sample program retrieves the first track, which is the sprite track, from the original movie, and sets the selection to the start of the movie ( Listing 3-14 ). The sample program iterates through all the tracks in the modifier movie, disposing of all non-video tracks.

Next, the sample program calls AddMovieSelection to add the modifier track to the original movie. Finally, the sample program calls AddTrackReference to associate the modifier track with the sprite track it will modify. AddTrackReference returns an index of the added reference in the referenceIndex variable.

Listing 14 Adding the modifier track to the movie



 
Movie           m;

TimeValue       oldDuration;

Movie           movieB;

long            i, origTrackCount, referenceIndex;

Track           newTrack, spriteTrack;



// get the first track in original movie and position at the start

spriteTrack = GetMovieIndTrack (m, 1);

SetMovieSelection (m, 0 ,0);



// remove all tracks except video in modifier movie

for (i = 1; i <= GetMovieTrackCount (movieB); i++) 

{

    Track t = GetMovieIndTrack (movieB, i);

    OSType aType;



    GetMediaHandlerDescription (GetTrackMedia(t), &aType, nil, nil);

    if (aType != VideoMediaType) 

    {

        DisposeMovieTrack (t);

        i--;

    }

}



// add the modifier track to original movie

oldDuration = GetMovieDuration (m);

AddMovieSelection (m, movieB);

DisposeMovie (movieB);



// truncate the movie to the length of the original track

DeleteMovieSegment (m, oldDuration, 

    GetMovieDuration (m) - oldDuration);



// associate the modifier track with the original sprite track

newTrack = GetMovieIndTrack (m, origTrackCount + 1);

AddTrackReference (spriteTrack, newTrack, kTrackModifierReference,

    &referenceIndex);

Besides adding a reference to the modifier track, the sample program must update the sprite media's input map to describe how the modifier track should be interpreted by the sprite track. The sample program performs the following tasks ( Listing 3-15 ):

It retrieves the sprite track's media by calling GetTrackMedia.
It calls GetMediaInputMap to retrieve the media's input map.
It adds a parent atom to the input map of type kTrackModifierInput . The ID of the atom is the reference index retrieved by the AddTrackReference function.
It adds two child atoms, one that specifies that the input type of the modifier track is of type kTrackModifierTypeImage, and one that specifies the index of the sprite image to override.
It calls SetMediaInputMap to update the media's input map.

Listing 15 Updating the media's input map



 
#define kImageIndexToOverride 1



Movie           m, movieB;

long            referenceIndex, imageIndexToOverride;

Track           spriteTrack;

QTAtomContainer inputMap;

QTAtom          inputAtom;

OSType          inputType;

Media           spriteMedia;



// get the sprite media's input map

spriteMedia = GetTrackMedia (spriteTrack);

GetMediaInputMap (spriteMedia, &inputMap);



// add an atom for a modifier track

QTInsertChild (inputMap, kParentAtomIsContainer,

    kTrackModifierInput, referenceIndex, 0, 0, nil, &inputAtom);



// add a child atom to specify the input type

inputType = kTrackModifierTypeImage;

QTInsertChild (inputMap, inputAtom, kTrackModifierType, 1, 0, 

    sizeof(inputType), &inputType, nil);



// add a second child atom to specify index of image to override

imageIndexToOverride = kImageIndexToOverride;

QTInsertChild (inputMap, inputAtom, kSpritePropertyImageIndex, 1, 0, 

    sizeof(imageIndexToOverride), &imageIndexToOverride, nil);



// update the sprite media's input map

SetMediaInputMap (spriteMedia, inputMap);

QTDisposeAtomContainer (inputMap);

Once the media's input map has been updated, the application can save the movie.