Inside Macintosh: QuickTime /

Chapter 2 - Movie Toolbox / Using the Movie Toolbox

Working With Movie Spatial Characteristics

The following section provides an example of how to create a track matte.

Listing 2-15 provides an example of how to create a track matte. The CreateTrackMatte function adds an uninitialized, 8-bit-deep, grayscale matte to a track. The UpdateTrackMatte function draws a gray ramp rectangle around the edge of the matte and fills the center of the matte with black. (A ramp rectangle shades gradually from light to dark in smooth increments.)

Listing 2-15 Creating a track matte

void CreateTrackMatte (Track theTrack)
{
   QDErr err;
   GWorldPtr aGW;
   Rect trackBox;
   Fixed trackHeight;
   Fixed trackWidth;
   CTabHandle grayCTab;

   GetTrackDimensions (theTrack, &trackWidth, &trackHeight);
   SetRect (&trackBox, 0, 0, FixRound (trackWidth),
             FixRound (trackHeight));
grayCTab = GetCTable(40);  /* 8 bit + 32 = 8 bit gray */
   err = NewGWorld (&aGW, 8, &trackBox, grayCTab,
                   (GDHandle) nil, 0);
   DisposeCTable (grayCTab);
   if (!err && (aGW != nil)) 
   {
      SetTrackMatte (theTrack, aGW->portPixMap);
      DisposeGWorld (aGW);
   }
}

void UpdateTrackMatte (Track theTrack)
{
   OSErr err;
   PixMapHandle trackMatte;
   PixMapHandle savePortPix;
   Movie    theMovie;
   GWorldPtr tempGW;
   CGrafPtr savePort;
   GDHandle saveGDevice;
   Rect     matteBox;
   short    i;
theMovie = GetTrackMovie (theTrack);
   trackMatte = GetTrackMatte (theTrack);
   if (trackMatte == nil) 
   {
      /* track doesn't have a matte, so give it one */
      CreateTrackMatte (theTrack);
      trackMatte = GetTrackMatte (theTrack);
      if (trackMatte == nil)
         return;
   }
GetGWorld (&savePort, &saveGDevice);
   matteBox = (**trackMatte).bounds;
   err = NewGWorld(&tempGW, 
                     (**trackMatte).pixelSize, &matteBox,
                     (**trackMatte).pmTable, (GDHandle) nil, 0);
   if (err || (tempGW == nil)) return;
SetGWorld (tempGW, nil);
   savePortPix = tempGW->portPixMap;
   LockPixels (trackMatte);
   SetPortPix (trackMatte);
/* draw a gray ramp rectangle around the edge of the matte */
   for (i = 0; i < 35; i++)  
   {
      RGBColor aColor;
      long     tempLong;

      tempLong = 65536 - ((65536 / 35) * (long)i);
      aColor.red = aColor.green = aColor.blue = tempLong;
      RGBForeColor(&aColor);
      FrameRect (&matteBox);
      InsetRect (&matteBox, 1, 1);
   }
   
   /* fill the center of the matte with black */
   ForeColor (blackColor);
   PaintRect (&matteBox);
   
   SetPortPix (savePortPix);
   SetGWorld (savePort, saveGDevice);
   DisposeGWorld (tempGW);

   UnlockPixels (trackMatte);
   SetTrackMatte (theTrack, trackMatte);

   DisposeMatte (trackMatte);
}